1.管道创建后父进程和子进程都拿到了管道的读写端描述符。各个进程根据所需关闭端口。
2.不同的读写端关闭情况,会产生不同的读写结果。
3.测试代码:
#include
#include
#include
#include
#if 0
int main(int * argc, const char * agrv[])
{
int fd[2];
pipe(fd);
pid_t pid = fork();
// while(1)
// {
if(pid == 0)//子进程
{
//close(fd[0]);//子进程写pipe,关闭读端
//dup2(STDOUT_FILENO,fd[1]);
dup2(fd[1],STDOUT_FILENO);//ps命令输出到标准输出设备,需要重定向到pipe的写端
execlp(“ps”,“ps”,“aux”,NULL);
}
else if(pid > 0) //父进程
{
//close(fd[1]);//父进程读pipe,关闭写端
//dup2(STDIN_FILENO,fd[0]);
dup2(fd[0],STDIN_FILENO);//grep命令从标准输入接收数据,现在需要从pipe的读端读数据,所有需要把标准输入重定向到pipe的读端p[0]
execlp(“grep”,“grep”,“bash”,NULL);
}
// }
return 0;
}
#endif
#if 0
int main(int * argc, const char * agrv[])
{
pid_t pid;
int fd[2];
pipe(fd);
int i;
for(i = 0; i<2; i++)
{
pid = fork();
if(pid == 0) break;
}
if(pid > 0) //父进程
{printf("I am father, pid:%d\n",getpid());close(fd[0]);close(fd[1]);// int status;// while(1) {// sleep(1);// int ret = waitpid(-1,&status,WNOHANG);// //int ret = wait(&status);// if(WIFEXITED(status)) printf("recycle child , status:%d\n", WEXITSTATUS(status));// if(WIFSIGNALED(status)) printf("recycle child , with status:%d\n", WTERMSIG(status));// }
}
else if( pid == 0)
{ if(i == 0)//子进程1{sleep(1);//保证父进程先执行printf("I am child1, pid:%d\n",getpid());close(fd[0]);//子进程写pipe,关闭读端//dup2(STDOUT_FILENO,fd[1]);dup2(fd[1],STDOUT_FILENO);//ps命令输出到标准输出设备,需要重定向到pipe的写端execlp("ps","ps","aux",NULL);close(fd[1]);exit(1);} else if(i == 1) //子进程2{sleep(2);//保证父进程和子进程1先执行printf("I am child2, pid:%d\n",getpid());close(fd[1]);//子进程2读pipe,关闭写端//dup2(STDIN_FILENO,fd[0]);dup2(fd[0],STDIN_FILENO);//grep命令从标准输入接收数据,现在需要从pipe的读端读数据,所有需要把标准输入重定向到pipe的读端p[0]execlp("grep","grep","bash",NULL);close(fd[0]);exit(1);}
}return 0;
}
#endif
int main(int * argc, const char * argv[])
{
int fd[2];//
pipe(fd);
pid_t pid = fork();if(pid == 0)
{sleep(1);close(fd[0]);//先关闭读端char buf[] = {"hello world"};close(fd[1]);//管道写端也关闭//write(fd[1],buf,sizeof(buf));//close(fd[1]);//子进程关闭写端while(1){write(fd[1],buf,sizeof(buf));perror("write pipe:");sleep(1);}
}
else if(pid > 0) //父进程读管道
{sleep(2);close(fd[1]);//父进程关闭写端//close(fd[0]);char buf[20];int status;while(1) {int ret = read(fd[0],buf,5);//读管道//printf("read data %s, ret = %d\n",buf, ret);sleep(1);int wret = waitpid(-1,&status,WNOHANG);//int wret = wait(&status);if(WIFEXITED(status)) printf("recycle child , status:%d\n", WEXITSTATUS(status));if(WIFSIGNALED(status)) printf("recycle child , with status:%d\n", WTERMSIG(status));}
}
}