exit()函数详解与Exit() 和 Return() 的区别

news/2024/5/18 21:51:09 标签: signal, 编译器, c

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color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; line-height:28px"> color:rgb(198,10,0); padding:0px; margin:0px">exit(0) 表示程序正常, color:rgb(198,10,0); padding:0px; margin:0px">exit(color:rgb(198,10,0); padding:0px; margin:0px">1)/color:rgb(198,10,0); padding:0px; margin:0px">exit(-color:rgb(198,10,0); padding:0px; margin:0px">1)表示程序异常退出

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exit() 结束当前进程/当前程序/࿰c;在整个程序中࿰c;只要调用 exit ࿰c;就结束

return() 是当前函数返回࿰c;当然如果是在主函数main, 自然也就结束当前进程了࿰c;如果不是࿰c;那就是退回上一层调用。在多个进程时.如果有时要检测上进程是否正常退出的.就要用到上个进程的返回值..

exit(1)表示进程正常退出. 返回 1;

exit(0)表示进程非正常退出. 返回 0.

color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">

color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px"> color:#800080; padding:0px; margin:0px">进程环境与进程控制(1): 进程的开始与终止

color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px"> 1. 进程的开始:
C程序是从main函数开始执行, 原型如下:
color:#000000; padding:0px; margin:0px">class="Code" style="padding:0px 5px; margin:0px; border:1px solid rgb(139,69,19); color:rgb(0,0,102); font-family:'Courier New',monospace; background-color:rgb(255,153,51)">int main(int argc, char *argv[]);
通常main的返回值是int型, 正确返回0.
如果main的返回值为void或者无, 某些class="tags" href="/tags/BianYiQi.html" title=编译器>编译器会给出警告, 此时main的返回值通常是0.

color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px"> 关于main的命令行参数不做过多解释, 以下面的程序展示一下:

class="Code" style="padding:0px 5px; margin:0px; border:1px solid rgb(139,69,19); color:rgb(0,0,102); font-family:'Courier New',monospace; background-color:rgb(255,153,51); font-size:14px; line-height:28px">

#include <stdio.h>

int main(int argc, char *argv[])
{
     int i;
     for (i = 0; i < argc; i++)
         printf("argv[%d]: %s\n", i, argv[i]);
     return 0;
}

2. 进程终止:
C程序的终止分为两种: 正常终止和异常终止.
正常终止分为: return, exit, _exit, _Exit, pthreade_exit
异常中指分为: abort, SIGNAL, 线程响应取消
主要说一下正常终止的前4种, 即exit系列函数.
class="Code" style="padding:0px 5px; margin:0px; border:1px solid rgb(139,69,19)">#include <stdlib.h> /* ISO C */
void exit(int status);
void _Exit(int status);
#include <unistd.h> /* POSIX */
void _exit(int status);
以上3个函数的区别是:
exit()(或return 0)会调用终止处理程序和用户空间的标准I/O清理程序(如fclose), _exit和_Exit不调用而直接由内核接管进行清

理.
因此, 在main函数中exit(0)等价于return 0.

3. atexit终止处理程序:
ISO C规定, 一个进程最对可登记32个终止处理函数, 这些函数由exit按登记相反的顺序自动调用. 如果同一函数登记多次, 也会被

调用多次.
原型如下:
class="Code" style="padding:0px 5px; margin:0px; border:1px solid rgb(139,69,19)">#include <stdlib.h>
int atexit(void (*func)(void));
其中参数是一个函数指针, 指向终止处理函数, 该函数无参无返回值.

以下面的程序为例:

class="Code" style="padding:0px 5px; margin:0px; border:1px solid rgb(139,69,19)">

#include <stdlib.h>

static void myexit1()
{
printf("first exit handler\n");
}

static void myexit2()
{
printf("second exit handler\n");
}

int main()
{
     if (atexit(my_exit2) != 0)
         printf("can't register my_exit2\n");
     if (atexit(my_exit1) != 0)
         printf("can't register my_exit1\n");
     if (atexit(my_exit1) != 0)
         printf("can't register my_exit1\n");

printf("main is done\n");
return 0;
}

运行结果:
$ ./a.out
main is done
first exit handler
first exit handler
second exit handler color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">运行结果:
color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px" /> color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">$./a.out arg1 arg2 arg3
color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px" /> color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">argv[0]: ./a.out
color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px" /> color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">argv[1]: arg1
color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px" /> color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">argv[2]: arg2
color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px" /> color:rgb(85,85,85); font-family:宋体,'Arial Narrow',arial,serif; font-size:14px; line-height:28px">argv[3]: arg3

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