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<?xml version="1.0" encoding="utf-8"?>
<search>
<entry>
<title>The hiding rule in C++</title>
<link href="/2019/09/13/The-hiding-rule-in-C/"/>
<url>/2019/09/13/The-hiding-rule-in-C/</url>
<content type="html"><![CDATA[<h2 id="是什么"><a href="#是什么" class="headerlink" title="是什么"></a>是什么</h2><p>更里层的scope里的变量名会使外层的同名变量被隐藏，即使该名字是一个签名不一样的函数。</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">#include <iostream></span><br><span class="line">#include <typeinfo></span><br><span class="line">using namespace std;</span><br><span class="line"></span><br><span class="line">namespace A {</span><br><span class="line"> char x;</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line">namespace B {</span><br><span class="line"> using namespace A;</span><br><span class="line"> int x;</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line">int main() {</span><br><span class="line"> cout << typeid(B::x).name() << endl;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p>将会输出：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">int</span><br></pre></td></tr></table></figure></p><h2 id="问题"><a href="#问题" class="headerlink" title="问题"></a>问题</h2><p>如果在继承类里定义一个函数<code>f</code>, 则基类里的所有名为<code>f</code>的函数都将被隐藏，即使返回类型和参数不一样。<br><a id="more"></a><br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">struct A {</span><br><span class="line"> void f() { }</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line">struct B : A {</span><br><span class="line"> void f(int) { }</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line">int main() {</span><br><span class="line"> B obj_B;</span><br><span class="line"> obj_B.f(3);</span><br><span class="line">// obj_B.f(); // 编译报错 f()未定义</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p><p>我们可以用<code>using</code>声明使基类的所有<code>f</code>可见。继承类里的重定义会覆盖基类的定义。<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line">#include <iostream></span><br><span class="line">using namespace std;</span><br><span class="line"></span><br><span class="line">struct A {</span><br><span class="line"> void f() { cout << "void A::f()" << endl; }</span><br><span class="line"> void f(int) { cout << "void A::f(int)" << endl; }</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line">struct B : A {</span><br><span class="line"> using A::f;</span><br><span class="line"> void f(int) { cout << "void B::f(int)" << endl; }</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line">int main() {</span><br><span class="line"> B obj_B;</span><br><span class="line"> obj_B.f(3);</span><br><span class="line"> obj_B.f();</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p><p>将会输出：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">void B::f(int)</span><br><span class="line">void A::f()</span><br></pre></td></tr></table></figure></p><h2 id="Public-Overloaded-Non-Virtuals-Call-Protected-Non-Overloaded-Virtuals"><a href="#Public-Overloaded-Non-Virtuals-Call-Protected-Non-Overloaded-Virtuals" class="headerlink" title="Public Overloaded Non-Virtuals Call Protected Non-Overloaded Virtuals"></a>Public Overloaded Non-Virtuals Call Protected Non-Overloaded Virtuals</h2><p>将本需使用<code>public</code>重载虚函数来定义的一组函数，通过<code>public</code>重载非虚函数和<code>protected</code>不重载虚函数这种方式来定义。如：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">class Base {</span><br><span class="line">public:</span><br><span class="line"> virtual void f(int x);</span><br><span class="line"> virtual void f(double x);</span><br><span class="line">};</span><br></pre></td></tr></table></figure></p><p>可定义为：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">class Base {</span><br><span class="line">public:</span><br><span class="line"> void f(int x) { f_int(x); } // Non-virtual</span><br><span class="line"> void f(double x) { f_dbl(x); } // Non-virtual</span><br><span class="line">protected:</span><br><span class="line"> virtual void f_int(int);</span><br><span class="line"> virtual void f_dbl(double);</span><br><span class="line">};</span><br></pre></td></tr></table></figure></p><p>这种方式下，隐藏规则导致的风险在基类处理掉了。</p><p><strong>参考</strong></p><p><a href="https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.cbclx01/name_hiding.htm" target="_blank" rel="noopener">Name hiding - IBM Knowledge Center</a></p><p><a href="https://www.ibm.com/support/knowledgecenter/SSLTBW_2.1.0/com.ibm.zos.v2r1.cbclx01/overload_member_fn_base_derived.htm" target="_blank" rel="noopener">Overloading member functions from base and derived classes - IBM Knowledge Center</a></p><p><a href="https://isocpp.org/wiki/faq/strange-inheritance#protected-virtuals" target="_blank" rel="noopener">Should I use protected virtuals instead of public virtuals? - isocpp</a></p>]]></content>
<categories>
<category> C/C++ </category>
</categories>
<tags>
<tag> hide </tag>
<tag> inheritance </tag>
</tags>
</entry>
<entry>
<title>Array Left Rotation</title>
<link href="/2017/08/23/array-left-rotation/"/>
<url>/2017/08/23/array-left-rotation/</url>
<content type="html"><![CDATA[<blockquote><p>A <em>left rotation</em> operation on an array of size n shifts each of the array’s elements 1 unit to the left. For example, if 2 left rotations are performed on array [1, 2, 3, 4, 5], then the array would become [3, 4, 5, 1, 2] .<br>Given an array of n integers a, and a number k, perform k left rotations on the array.</p></blockquote><p><a href="https://www.hackerrank.com/challenges/ctci-array-left-rotation/problem" target="_blank" rel="noopener">HackerRank</a></p><p>Here we want solutions with O(1) additional space and O(n) time complexity.<br><a id="more"></a></p><h1 id="My-solution"><a href="#My-solution" class="headerlink" title="My solution"></a>My solution</h1><p> Note that the element at index <code>i</code> is moved to <code>(i-k) % n</code>.<br> Let n = 15 and k = 6, then </p><p> a[0] <- a[6] <- a[12] <- a[3] <- a[9] <- a[0],</p><p> a[1] <- a[7] <- a[13] <- a[4] <- a[10] <- a[1],</p><p> a[2] <- a[8] <- a[14] <- a[5] <- a[11] <- a[2].</p><p> Clearly, it forms 3 circles, and the 3 circles cover all the movement. 3 is the greatest common divisor (gcd) of 15 and 6.</p><p> It should be easy to prove that, the rotation can be broken down to g (gcd of n and k) smaller circles, and within every circle are elements at index i, (i+k)%n, … We only need to rotate each circle by one step.</p><figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string"><iostream></span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string"><vector></span></span></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="built_in">std</span>;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">gcd</span><span class="params">(<span class="keyword">int</span> a, <span class="keyword">int</span> b)</span> </span>{</span><br><span class="line"> <span class="keyword">if</span> (b==<span class="number">0</span>) <span class="keyword">return</span> a;</span><br><span class="line"> <span class="keyword">else</span> <span class="keyword">return</span> gcd(b, a%b);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="built_in">vector</span><<span class="keyword">int</span>> array_left_rotation(<span class="built_in">vector</span><<span class="keyword">int</span>> a, <span class="keyword">int</span> n, <span class="keyword">int</span> k) {</span><br><span class="line"> <span class="keyword">if</span> (k==n) <span class="keyword">return</span> a;</span><br><span class="line"> <span class="keyword">int</span> g = gcd (n, k);</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> j=<span class="number">0</span>; j< g; j++) { </span><br><span class="line"> <span class="keyword">int</span> tmp = a[j], i = j, to_i = (i+k)%n;</span><br><span class="line"> <span class="keyword">while</span> (to_i !=j) {</span><br><span class="line"> a[i] = a[to_i];</span><br><span class="line"> i = to_i;</span><br><span class="line"> to_i = (i+k)%n;</span><br><span class="line"> }</span><br><span class="line"> a[i] = tmp;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> a;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span>{</span><br><span class="line"> <span class="keyword">int</span> n;</span><br><span class="line"> <span class="keyword">int</span> k;</span><br><span class="line"> <span class="built_in">cin</span> >> n >> k;</span><br><span class="line"> <span class="built_in">vector</span><<span class="keyword">int</span>> a(n);</span><br><span class="line"> <span class="keyword">for</span>(<span class="keyword">int</span> a_i = <span class="number">0</span>;a_i < n;a_i++){</span><br><span class="line"> <span class="built_in">cin</span> >> a[a_i];</span><br><span class="line"> }</span><br><span class="line"> <span class="built_in">vector</span><<span class="keyword">int</span>> output = array_left_rotation(a, n, k);</span><br><span class="line"> <span class="keyword">for</span>(<span class="keyword">int</span> i = <span class="number">0</span>; i < n;i++)</span><br><span class="line"> <span class="built_in">cout</span> << output[i] << <span class="string">" "</span>;</span><br><span class="line"> <span class="built_in">cout</span> << <span class="built_in">endl</span>;</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p>There is another solution from the book, <em>Programming Pearls</em>.</p><h1 id="Solution-2"><a href="#Solution-2" class="headerlink" title="Solution 2"></a>Solution 2</h1><p><strong>Observation</strong>:</p><p>for an array {a[0], a[1],… a[k-1], a[k], a[k+1],…a[n-1]}, after the rotation, it becomes {a[k], a[k+1]…a[n-1], a[0], a[1]… a[k-1]}. Let’s notate the a[0]~a[k-1] part as A, the latter part a[k]~ a[n-1] as B. Then what the rotation does is actually transfering AB to BA.</p><p><strong>Solution</strong>: </p><ul><li>First, reverse AB as a whole: AB -> BrAr.</li><li>Then, reverse Ar, Br individually: BrAr -> BA</li></ul><figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// pay attention to the & in the parameter</span></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">swap</span><span class="params">(<span class="built_in">vector</span><<span class="keyword">int</span>> &a, <span class="keyword">int</span> m, <span class="keyword">int</span> l)</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> tmp = a[m];</span><br><span class="line"> a[m] = a[l];</span><br><span class="line"> a[l] = tmp;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"><span class="built_in">vector</span><<span class="keyword">int</span>> array_left_rotation(<span class="built_in">vector</span><<span class="keyword">int</span>> a, <span class="keyword">int</span> n, <span class="keyword">int</span> k) {</span><br><span class="line"> <span class="keyword">if</span> (k==n) <span class="keyword">return</span> a;</span><br><span class="line"> <span class="comment">// reverse AB as a whole</span></span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i=<span class="number">0</span>; i < n<span class="number">-1</span>-i; i++) {</span><br><span class="line"> swap(a, i, n<span class="number">-1</span>-i);</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// reverse Br</span></span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i=<span class="number">0</span>; i< n-k<span class="number">-1</span>-i; i++) {</span><br><span class="line"> swap(a, i, n-k<span class="number">-1</span>-i);</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// reverse Ar</span></span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i= n-k; i < <span class="number">2</span>*n-k-i<span class="number">-1</span>;i++) {</span><br><span class="line"> swap(a, i, <span class="number">2</span>*n-k-i<span class="number">-1</span>);</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> a;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p>This works, but it’s kind of tiring to get all the indices right to the <code>swap()</code> call.<br>Let’s try with a <code>reverse()</code> helper function. And also, reverse A, B individually first, and then reverse ArBr as a whole, then we get BA.</p><figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">reverse</span><span class="params">(<span class="built_in">vector</span><<span class="keyword">int</span>> &a, <span class="keyword">int</span> low, <span class="keyword">int</span> high)</span> </span>{</span><br><span class="line"> <span class="keyword">while</span> (low < high) {</span><br><span class="line"> <span class="keyword">int</span> tmp = a[low];</span><br><span class="line"> a[low] = a[high];</span><br><span class="line"> a[high] = tmp;</span><br><span class="line"> low++; high--;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="built_in">vector</span><<span class="keyword">int</span>> array_left_rotation(<span class="built_in">vector</span><<span class="keyword">int</span>> a, <span class="keyword">int</span> n, <span class="keyword">int</span> k) {</span><br><span class="line"> <span class="keyword">if</span> (k==n) <span class="keyword">return</span> a;</span><br><span class="line"> <span class="comment">// reverse A</span></span><br><span class="line"> reverse(a, <span class="number">0</span>, k<span class="number">-1</span>);</span><br><span class="line"> <span class="comment">// reverse B</span></span><br><span class="line"> reverse(a, k, n<span class="number">-1</span>);</span><br><span class="line"> <span class="comment">// reverse ArBr as a whole</span></span><br><span class="line"> reverse(a, <span class="number">0</span>, n<span class="number">-1</span>);</span><br><span class="line"> <span class="keyword">return</span> a;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>]]></content>
<categories>
<category> algorithm </category>
</categories>
<tags>
<tag> rotation </tag>
</tags>
</entry>
<entry>
<title>shell tips</title>
<link href="/2017/05/11/shell-tips/"/>
<url>/2017/05/11/shell-tips/</url>
<content type="html"><![CDATA[<h2 id="通配符"><a href="#通配符" class="headerlink" title="通配符 *"></a>通配符 *</h2><p>shell 将通配符<code>*</code>替换为当前目录下的各个文件和目录，然后再传给命令。<br>比如<code>ls *</code>是ls(<code>当前目录下的所有文件</code> + <code>当前目录下所有文件夹</code>), 其中ls(<code>当前目录下所有文件夹</code>) 将会列举这些文件夹下的文件(夹)</p><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">➜ ls -p <span class="comment"># append '/' at the end of a directory</span></span><br><span class="line">pkg/ tmp</span><br><span class="line"></span><br><span class="line">➜ ls *</span><br><span class="line">tmp</span><br><span class="line"></span><br><span class="line">pkg: <span class="comment"># list content in directory pkg</span></span><br><span class="line">a.tgz.gpg read.sh</span><br></pre></td></tr></table></figure><a id="more"></a><h2 id="括号和大括号"><a href="#括号和大括号" class="headerlink" title="括号和大括号"></a>括号和大括号</h2><p><code>()</code> 包裹的代码在子shell 里执行，<code>{}</code> 包含的代码在当前shell里执行<br><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">➜ (a=<span class="variable">$PWD</span>;<span class="built_in">echo</span> <span class="variable">$a</span>;)</span><br><span class="line">/Users/lin</span><br><span class="line">➜ <span class="built_in">echo</span> <span class="variable">$a</span> <span class="comment"># a is not defined in current shell</span></span><br><span class="line"></span><br><span class="line">➜ { a=<span class="variable">$PWD</span>;<span class="built_in">echo</span> <span class="variable">$a</span>; }</span><br><span class="line">/Users/lin</span><br><span class="line">➜ <span class="built_in">echo</span> <span class="variable">$a</span></span><br><span class="line">/Users/lin</span><br></pre></td></tr></table></figure></p><h2 id="echo-expression"><a href="#echo-expression" class="headerlink" title="echo $((expression))"></a>echo $((expression))</h2><p>运算展开<br><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">➜ <span class="built_in">echo</span> $((1+2))</span><br><span class="line">3</span><br></pre></td></tr></table></figure></p><p>进制</p><table><thead><tr><th>写法</th><th>含义 </th></tr></thead><tbody><tr><td><code>0</code>开头</td><td>8进制</td></tr><tr><td><code>0x</code>开头</td><td>16进制</td></tr><tr><td><code>[base#]n</code></td><td>base进制，n is a number in that base</td></tr></tbody></table><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">➜ <span class="built_in">echo</span> $((1))</span><br><span class="line">1</span><br><span class="line"></span><br><span class="line">➜ <span class="built_in">echo</span> $((2<span class="comment">#11))</span></span><br><span class="line">3</span><br><span class="line"></span><br><span class="line">➜ <span class="built_in">echo</span> $((2<span class="comment">#3))</span></span><br><span class="line">zsh: bad math expression: operator expected at `3<span class="string">'</span></span><br></pre></td></tr></table></figure><h2 id="单引号和双引号"><a href="#单引号和双引号" class="headerlink" title="单引号和双引号"></a>单引号和双引号</h2><p>被双引号括起的内容常量还是常量，变量则会替换成变量内容。<br>被单引号括起的内容不会发生替换。</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">➜ var=dablelv</span><br><span class="line">➜ echo '$var'</span><br><span class="line">$var</span><br><span class="line">➜ echo "$var"</span><br><span class="line">dablelv</span><br></pre></td></tr></table></figure><h2 id="To-be-continued"><a href="#To-be-continued" class="headerlink" title="To be continued."></a>To be continued.</h2>]]></content>
<categories>
<category> linux </category>
</categories>
<tags>
<tag> shell </tag>
</tags>
</entry>
<entry>
<title>typedef详解</title>
<link href="/2017/05/11/typedef%E8%AF%A6%E8%A7%A3/"/>
<url>/2017/05/11/typedef%E8%AF%A6%E8%A7%A3/</url>
<content type="html"><![CDATA[<p>一行很常用的代码：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="keyword">int</span> XX_Size_Check[(<span class="keyword">sizeof</span>(XX)==<span class="number">64</span>)? <span class="number">1</span>:<span class="number">-1</span>];</span><br></pre></td></tr></table></figure></p><p>很容易猜到上面这行代码是要在编译时检查XX的size，但再深究点，我们就会发现它跟我们平时typedef的写法不太一致。<br><a id="more"></a></p><h1 id="typedef用法小结"><a href="#typedef用法小结" class="headerlink" title="typedef用法小结"></a>typedef用法小结</h1><h2 id="对已有类型定义别名"><a href="#对已有类型定义别名" class="headerlink" title="对已有类型定义别名"></a>对已有类型定义别名</h2><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <old type name> <<span class="keyword">new</span> alias>;</span><br></pre></td></tr></table></figure><p>这是最常见的写法，主要用途有</p><ul><li>结构体</li></ul><p>举个例子，我们这里定义了一个结构体MyStruct，在C里面，如果要定义该类型的变量，则需要写struct关键字。(C++里在不产生歧义的情况下可以省略。）</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">MyStruct</span> {</span></span><br><span class="line"> <span class="keyword">int</span> data1;</span><br><span class="line"> <span class="keyword">char</span> data2;</span><br><span class="line">};</span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">MyStruct</span> <span class="title">a</span>;</span></span><br></pre></td></tr></table></figure><p>我们可以使用typedef来简化书写：</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">MyStruct</span> <span class="title">newtype</span>;</span></span><br><span class="line"></span><br><span class="line">newtype a;</span><br></pre></td></tr></table></figure><p>当然也可以直接写成这样：</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">MyStruct</span> {</span></span><br><span class="line"> <span class="keyword">int</span> data1;</span><br><span class="line"> <span class="keyword">char</span> data2;</span><br><span class="line">} newtype;</span><br></pre></td></tr></table></figure><p>或者更简单的：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> {</span></span><br><span class="line"> <span class="keyword">int</span> data1;</span><br><span class="line"> <span class="keyword">char</span> data2;</span><br><span class="line">} newtype;</span><br></pre></td></tr></table></figure></p><ul><li>指针</li></ul><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="class"><span class="keyword">struct</span> <span class="title">Node</span>* <span class="title">NodePtr</span>;</span></span><br><span class="line">...</span><br><span class="line">NodePtr startptr, endptr, curptr, prevptr, errptr, refptr;</span><br></pre></td></tr></table></figure><h2 id="函数指针"><a href="#函数指针" class="headerlink" title="函数指针"></a>函数指针</h2><p>不使用typedef，我们会这样写：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">do_math</span><span class="params">(<span class="keyword">float</span> arg1, <span class="keyword">int</span> arg2)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> arg2;</span><br><span class="line">}</span><br><span class="line"> </span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">call_a_func</span><span class="params">(<span class="keyword">int</span> (*call_this)(<span class="keyword">float</span>, <span class="keyword">int</span>))</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> output = call_this(<span class="number">5.5</span>, <span class="number">7</span>);</span><br><span class="line"> <span class="keyword">return</span> output;</span><br><span class="line">}</span><br><span class="line"> </span><br><span class="line"><span class="keyword">int</span> final_result = call_a_func(&do_math);</span><br></pre></td></tr></table></figure></p><p>使用typedef：<br><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">typedef</span> <span class="title">int</span> <span class="params">(*MathFunc)</span><span class="params">(<span class="keyword">float</span>, <span class="keyword">int</span>)</span></span>;</span><br><span class="line"> </span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">do_math</span><span class="params">(<span class="keyword">float</span> arg1, <span class="keyword">int</span> arg2)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> arg2;</span><br><span class="line">}</span><br><span class="line"> </span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">call_a_func</span><span class="params">(MathFunc call_this)</span> </span>{</span><br><span class="line"> <span class="keyword">int</span> output = call_this(<span class="number">5.5</span>, <span class="number">7</span>);</span><br><span class="line"> <span class="keyword">return</span> output;</span><br><span class="line">}</span><br><span class="line"> </span><br><span class="line"><span class="keyword">int</span> final_result = call_a_func(&do_math);</span><br></pre></td></tr></table></figure></p><p>这里typedef后面跟了一个函数指针类型 int (*MathFunc)(float, int)，通过这个语句，MathFunc成为该函数指针类型的别名。</p><h2 id="数组"><a href="#数组" class="headerlink" title="数组"></a>数组</h2><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="keyword">int</span> <span class="built_in">vector</span>[<span class="number">10</span>];</span><br><span class="line"></span><br><span class="line"><span class="built_in">vector</span> a;</span><br><span class="line">a[<span class="number">9</span>] = <span class="number">100</span>;</span><br></pre></td></tr></table></figure><p>和函数指针比较类似，typedef后面跟了一个数组类型（元素类型为int，数组长度为10），通过这个语句，vector成为该数组类型的别名。<br>也可以定义多维数组。</p><h3 id="参考："><a href="#参考：" class="headerlink" title="参考："></a>参考：</h3><p><a href="http://en.wikipedia.org/wiki/Typedef" target="_blank" rel="noopener">Wikipedia: typedef</a></p><p><a href="http://www.cnblogs.com/Jason-Damon/archive/2011/10/23/2222119.html" target="_blank" rel="noopener">Jason Damon: 使用typedef语句定义数组类型</a></p>]]></content>
<categories>
<category> C/C++ </category>
</categories>
<tags>
<tag> typedef </tag>
</tags>
</entry>
<entry>
<title>hexo搭建博客全记录</title>
<link href="/2017/04/18/hexo%E6%90%AD%E5%BB%BA%E5%8D%9A%E5%AE%A2%E5%85%A8%E8%AE%B0%E5%BD%95/"/>
<url>/2017/04/18/hexo%E6%90%AD%E5%BB%BA%E5%8D%9A%E5%AE%A2%E5%85%A8%E8%AE%B0%E5%BD%95/</url>
<content type="html"><![CDATA[<h1 id="why-hexo"><a href="#why-hexo" class="headerlink" title="why hexo"></a>why hexo</h1><p>曾经尝试过用github pages搭博客，用的是<a href="http://isnowfy.github.io/about-simple-cn.html" target="_blank" rel="noopener">isnowfy</a>提供的框架，但是有几个缺点：</p><ul><li>发文章必须用它提供的框架，且需要将Github用户名和密码告诉它</li><li>网站样式不好看，懒癌又不会自己调整</li><li>网站自定义的维度比较小</li></ul><p>最近看了几个用hexo搭的博客，功能基本满足我的需求，且颜值高，就果断折腾一波，我用的是Mac 。参考：</p><ul><li><a href="http://www.ezlippi.com/" target="_blank" rel="noopener">EZLippi-浮生志</a></li><li><a href="https://hexo.io/" target="_blank" rel="noopener">hexo官网</a></li><li><a href="http://theme-next.iissnan.com/" target="_blank" rel="noopener">NexT主题官网</a><a id="more"></a><h1 id="基础"><a href="#基础" class="headerlink" title="基础"></a>基础</h1>基础操作参考官网文档即可，<a href="http://www.jianshu.com/p/4eaddcbe4d12" target="_blank" rel="noopener">5分钟搭建免费个人博客 - dimsky</a> 这个比较简洁。</li></ul><h2 id="node安装慢"><a href="#node安装慢" class="headerlink" title="node安装慢"></a>node安装慢</h2><p>推荐安装nvm，然后用它装node；node国内下载超级慢，得用镜像。<br><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">export</span> NVM_NODEJS_ORG_MIRROR=https://npm.taobao.org/mirrors/node</span><br></pre></td></tr></table></figure></p><p>将这行配置加到你的shell的配置文件如<em>.zshrc</em>里，然后<code>source ~/.zshrc</code>。</p><p>另附上npm的国内镜像：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"># 编辑 ~/.npmrc 加入下面内容</span><br><span class="line">registry = https://registry.npm.taobao.org</span><br></pre></td></tr></table></figure></p><h2 id="安装主题"><a href="#安装主题" class="headerlink" title="安装主题"></a>安装主题</h2><p>比如NexT<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">cd username.github.io</span><br><span class="line">git clone https://github.com/iissnan/hexo-theme-next themes/next</span><br></pre></td></tr></table></figure></p><h2 id="站点配置"><a href="#站点配置" class="headerlink" title="站点配置"></a>站点配置</h2><p>路径：username.github.io/<code>_config.yml</code>，参考：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">title: dimsky 的 9 维空间 //你博客的名字</span><br><span class="line">author: dimsky //你的名字</span><br><span class="line">language: zh-Hans //语言 中文</span><br><span class="line">theme: next //刚刚安装的主题名称</span><br><span class="line">deploy:</span><br><span class="line"> type: git //使用Git 发布</span><br><span class="line"> repo: https://github.com/username/username.github.io.git // 刚创建的Github仓库</span><br></pre></td></tr></table></figure></p><h2 id="主题配置"><a href="#主题配置" class="headerlink" title="主题配置"></a>主题配置</h2><p>路径：username.github.io<code>/themes/next/_config.yml</code>，参考：<a href="http://theme-next.iissnan.com/getting-started.html#theme-settings" target="_blank" rel="noopener">主题设定 - NexT</a></p><h2 id="命令汇总："><a href="#命令汇总：" class="headerlink" title="命令汇总："></a>命令汇总：</h2><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># nvm安装</span></span><br><span class="line">curl https://raw.githubusercontent.com/creationix/nvm/master/install.sh | sh</span><br><span class="line"><span class="comment"># nvm使用</span></span><br><span class="line">nvm ls-remote</span><br><span class="line">nvm ls</span><br><span class="line">nvm install stable</span><br><span class="line">nvm install 7 <span class="comment"># 会自动装7的最新版本</span></span><br><span class="line"><span class="comment"># nvm use</span></span><br><span class="line">nvm use 7.9.0</span><br><span class="line">nvm use system</span><br></pre></td></tr></table></figure><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># hexo安装</span></span><br><span class="line">npm install hexo-cli -g</span><br><span class="line">hexo init username.github.io</span><br><span class="line"><span class="built_in">cd</span> username.github.io</span><br><span class="line">npm install</span><br></pre></td></tr></table></figure><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 写文章</span></span><br><span class="line">hexo new [layout] <title></span><br><span class="line"><span class="comment"># 启动本地服务</span></span><br><span class="line">hexo s</span><br><span class="line"><span class="comment"># 安装hexo-deployer-git</span></span><br><span class="line">npm install hexo-deployer-git --save</span><br><span class="line"><span class="comment"># 清理缓存db.json和生成文件(public)，generate，deploy</span></span><br><span class="line">hexo clean && hexo g && hexo d</span><br></pre></td></tr></table></figure><h1 id="进阶"><a href="#进阶" class="headerlink" title="进阶"></a>进阶</h1><h2 id="主题配置-1"><a href="#主题配置-1" class="headerlink" title="主题配置"></a>主题配置</h2><ul><li>添加tags，categories，about页面</li><li>侧边栏社交链接</li><li>设置友情链接</li></ul><p>参考：<a href="http://theme-next.iissnan.com/theme-settings.html" target="_blank" rel="noopener">主题配置 - NexT</a></p><h2 id="站内搜索"><a href="#站内搜索" class="headerlink" title="站内搜索"></a>站内搜索</h2><p><a href="http://theme-next.iissnan.com/third-party-services.html#local-search" target="_blank" rel="noopener">Local Search - NexT</a><br><a href="http://www.ezlippi.com/blog/2017/02/hexo-search.html" target="_blank" rel="noopener">Hexo博客添加站内搜索 - EZLippi</a><br><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># npm install hexo-generator-search --save ?</span></span><br><span class="line">npm install hexo-generator-searchdb --save</span><br></pre></td></tr></table></figure></p><p>向站点配置文件添加<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">search:</span><br><span class="line"> path: search.xml</span><br><span class="line"> field: post</span><br><span class="line"> format: html</span><br><span class="line"> limit: 10000</span><br></pre></td></tr></table></figure></p><p>编辑主题配置文件，启用本地搜索功能：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">local_search:</span><br><span class="line"> enable: true</span><br></pre></td></tr></table></figure></p><p>注意缩进。</p><h2 id="站点地图"><a href="#站点地图" class="headerlink" title="站点地图"></a>站点地图</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">npm install hexo-generator-seo-friendly-sitemap --save</span><br></pre></td></tr></table></figure><p>向站点配置文件添加<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">sitemap:</span><br><span class="line"> path: sitemap.xml</span><br></pre></td></tr></table></figure></p><h2 id="返回顶部"><a href="#返回顶部" class="headerlink" title="返回顶部"></a>返回顶部</h2><p>参考：<a href="http://wuchong.me/blog/2014/01/08/hexo-scrollup/" target="_blank" rel="noopener">Hexo博客优化：添加返回顶部功能 - Jark</a>，备个份。</p><ol><li><p>新建文件 username.github.io<code>/themes/next/layout/_partials/totop.ejs</code>，在文件中加入HTML代码：</p><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"totop"</span> <span class="attr">style</span>=<span class="string">"position:fixed;bottom:150px;right:50px;cursor: pointer;"</span>></span></span><br><span class="line"><span class="tag"><<span class="name">a</span> <span class="attr">title</span>=<span class="string">"返回顶部"</span>></span><span class="tag"><<span class="name">img</span> <span class="attr">src</span>=<span class="string">"/imgs/scrollup.png"</span>/></span><span class="tag"></<span class="name">a</span>></span></span><br><span class="line"><span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="comment"><!--文件引用--></span></span><br><span class="line"><span class="tag"><<span class="name">%-</span> <span class="attr">partial</span>('<span class="attr">totop</span>') %></span></span><br><span class="line"><span class="tag"><<span class="name">script</span> <span class="attr">src</span>=<span class="string">"<%- config.root %>js/totop.js"</span>></span><span class="tag"></<span class="name">script</span>></span></span><br></pre></td></tr></table></figure></li><li><p>新建文件 username.github.io<code>/themes/next/source/js/totop.js</code>，在文件中添加javascript代码：</p><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line">(<span class="function"><span class="keyword">function</span>(<span class="params">$</span>) </span>{ </span><br><span class="line"><span class="comment">// When to show the scroll link</span></span><br><span class="line"><span class="comment">// higher number = scroll link appears further down the page </span></span><br><span class="line"><span class="keyword">var</span> upperLimit = <span class="number">1000</span>;</span><br><span class="line"></span><br><span class="line"><span class="comment">// Our scroll link element</span></span><br><span class="line"><span class="keyword">var</span> scrollElem = $(<span class="string">'#totop'</span>);</span><br><span class="line"> </span><br><span class="line"><span class="comment">// Scroll to top speed</span></span><br><span class="line"><span class="keyword">var</span> scrollSpeed = <span class="number">500</span>;</span><br><span class="line"> </span><br><span class="line"><span class="comment">// Show and hide the scroll to top link based on scroll position </span></span><br><span class="line">scrollElem.hide();</span><br><span class="line">$(<span class="built_in">window</span>).scroll(<span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>{ </span><br><span class="line"><span class="keyword">var</span> scrollTop = $(<span class="built_in">document</span>).scrollTop(); </span><br><span class="line"><span class="keyword">if</span> ( scrollTop > upperLimit ) {</span><br><span class="line">$(scrollElem).stop().fadeTo(<span class="number">300</span>, <span class="number">1</span>); <span class="comment">// fade back in </span></span><br><span class="line">}<span class="keyword">else</span>{ </span><br><span class="line">$(scrollElem).stop().fadeTo(<span class="number">300</span>, <span class="number">0</span>); <span class="comment">// fade out</span></span><br><span class="line">}</span><br><span class="line">});</span><br><span class="line"><span class="comment">// Scroll to top animation on click</span></span><br><span class="line">$(scrollElem).click(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line">$(<span class="string">'html, body'</span>).animate({<span class="attr">scrollTop</span>:<span class="number">0</span>}, scrollSpeed); <span class="keyword">return</span> <span class="literal">false</span>;</span><br><span class="line">});</span><br><span class="line">})(jQuery);</span><br><span class="line"><span class="comment">// 如果对显示位置和回滚速度不满意，修改以上代码的upperLimit和scrollSpeed参数即可。</span></span><br></pre></td></tr></table></figure></li><li><p>添加按钮图片。将下图复制到 username.github.io<code>/themes/next/source/imgs</code> 目录下，文件名为<code>scrollup.png</code><br><img src="/images/scrollup.png" alt="scrollup.png"></p></li></ol><h1 id="TODO"><a href="#TODO" class="headerlink" title="TODO"></a>TODO</h1><ul><li><strong>评论区</strong> 多说快关闭了，需要考察下用什么</li><li><strong>博客迁移</strong> </li></ul>]]></content>
<categories>
<category> 杂 </category>
</categories>
<tags>
<tag> hexo </tag>
</tags>
</entry>
</search>