#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
int main()
{
    pid_t pid;
    int fd = open("test.txt",O_RDWR|O_CREAT|O_APPEND);
    if (fd == -1)
    {
        printf("open file error\n");
        return -1;
    }
    printf("fd = %d\n",fd);
    /*
    int val = 0;
    if((val = fcntl(fd,F_GETFD,0)) < 0)
    {
       printf("F_GETFL failed\n");
      return -1;
    }
    val |= FD_CLOEXEC;    
    if(fcntl(fd, F_SETFD, FD_CLOEXEC) < 0)
    {
        printf("F_SETFD failed\n");
        return -1;
    }  
    */                  
    char *s="parentparentparentparent";

    pid = fork();
    /*子进程*/
    if(pid == 0)
    {
        execl("child", "./child", &fd, NULL);
    }
    
    wait(NULL);
    write(fd,s,strlen(s));
    close(fd);
    return 0;
}

#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char *argv[])  
{  
    int fd;    
    fd = *argv[1];  
    printf("%d\n",fd);    
    char *s = "childchildchildchild";  
    if(write(fd, (void *)s, strlen(s)) != strlen(s))
    {
        printf("write error in child\n");
    }
    close(fd);  
    return 0;  
}