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c-and-cpp.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
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<title>Jerry的个人维基</title>
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<div id="content">
<h1 id="toc_1"> C & C++</h1>
<div class="toc">
<ul>
<li><a href="#toc_1"> C & C++</a></li>
<ul>
<li><a href="#toc_1.1">1. Traps and Pitfalls</a></li>
<li><a href="#toc_1.2">2. UNIX C</a></li>
<ul>
<li><a href="#toc_1.2.1">2.1. fork, waitpid and exit</a></li>
<li><a href="#toc_1.2.2">2.2. pthread</a></li>
</ul>
</ul>
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</div>
<h2 id="toc_1.1">1. Traps and Pitfalls</h2>
<ul>
<li>
一个布尔表达式里如果既有无符号整数，又有有符号整数，并且没有强制类型转换的话，C会将这些整数当作无符处理，从而得出很多非正常的结果。
</li>
</ul>
<p>
以下程序：
</p>
<pre class="brush: c;">
#include <stdio.h>
int main(int argc, const char *argv[])
{
unsigned x = 10;
printf ("x(10U) > -1 ? %d\n", (x > -1));
printf ("10 > -1 ? %d\n", (10 > -1));
printf ("10u > -1 ? %d\n", (10u > -1));
return 0;
}
</pre>
<p>
输出：
</p>
<pre class="brush: plain;">
x(10U) > -1 ? 0
10 > -1 ? 1
10u > -1 ? 0
</pre>
<h2 id="toc_1.2">2. UNIX C</h2>
<h3 id="toc_1.2.1">2.1. fork, waitpid and exit</h3>
<ul>
<li>
fork()在父进程里返回子进程的pid，在子进程里返回0，出错返回负值。
</li>
<li>
exit()传入的状态值会和0377做与运算以后（status & 0377）再返回给父进程。为什么？
</li>
<li>
通过waitpid()得到的子进程status需要通过一系列的宏做处理后才能进一步使用。
</li>
</ul>
<pre class="brush: c;">
waitpid(pid, &status, 0);
status = WEXITSTATUS(status);
printf("Sub process finished: %u, exit status: %d\n", pid, status);
</pre>
<h3 id="toc_1.2.2">2.2. pthread</h3>
<ul>
<li>
一个进程的多个线程完全共享了同样的地址空间，一个线程甚至能访问其他线程的堆栈（虽然这样做十分容易带来各种bug）
</li>
</ul>
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