kaka

apue笔记 

apue代码编译http://blog.163.com/casillas_yeah/blog/static/1041019820103505716852/

fork函数

#include<unistd.h>

pid_t  fork(void)

返回值：子进程中返回0,父进程中返回子进程ID，出错返回1

子进程获得父进程的数据空间，堆，和栈的副本，注意这是子进程所拥有的副本，父子进程并不共享存储空间，只共享正文段

#include<unistd.h>
#include<sys/types.h>
char buf[] = "a write to stdout\n";


int glob = 6;
int main(void)
{
	int var;
	pid_t pid;
	var = 88;
	
	if(write(STDOUT_FILENO,buf,sizeof(buf)-1) != sizeof(buf) - 1)
	printf("write error");
	
	printf("before fork\n");
	
	if((pid = fork()) < 0)printf("error");
	else if(pid == 0)
	{
		glob++;
		var++;
		printf("this is child process pid = %d\n",getpid());
		printf("this is child process my parentprocess pid = %d\n",getppid());
	}
	else
	{
		printf("this is parentprocess pid = %d\n",getpid());
		sleep(2);
	}
	printf("pid = %d,processpid = %d,glob = %d,var = %d\n",pid,getpid(),glob,var);
	exit(0);
}

输出

xiaobo@xiaobo-desktop:~/桌面/apue/myapue$ ./a.out
a write to stdout
before fork
pid = 2319,glob = 7,var = 89
pid = 2318,glob = 6,var = 88
xiaobo@xiaobo-desktop:~/桌面/apue/myapue$ ./a.out > temp.out
xiaobo@xiaobo-desktop:~/桌面/apue/myapue$ cat temp.out
a write to stdout
before fork
pid = 2323,glob = 7,var = 89
before fork
pid = 2322,glob = 6,var = 88

vfock函数