fcntl

 

//fcntl.c
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>

int set_fd(int);
int main()
{
        int fd,ret;
        char f[20];
        fd=open("pighead.txt",O_RDWR|O_CREAT);
        set_fd(fd);
        sprintf(f,"%d",fd);
        ret=execl("test",f,(char *)0);
        printf("ret:%d\n",ret);
        return 0;
}

int set_fd(int fd)
{
        unsigned int flag;
        flag=fcntl(fd,F_GETFD);
        flag|=~FD_CLOEXEC;
        //flag|=FD_CLOEXEC;
        fcntl(fd,F_SETFD,flag);
        return 0;
}

 

// test.c
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>

int main(int argc,char **argv)
{
int fd,ret;
system("echo abc >te.log");
printf("argv[0]:%s, argv[1]:%s\n",argv[0],argv[1]);
fd=atoi(argv[0]);
char str[16];
strcpy(str,"hello,world~\n");

printf("%s",str);
ret=write(fd,str,strlen(str));
printf("ret:%d\n",ret);
return 0;
}

mutian@mutian:~/Downloads/temp/test$ ls
fcntl.c  test.c
mutian@mutian:~/Downloads/temp/test$ g++ -o fcntl fcntl.c
mutian@mutian:~/Downloads/temp/test$ g++ -o test test.c
mutian@mutian:~/Downloads/temp/test$
mutian@mutian:~/Downloads/temp/test$
mutian@mutian:~/Downloads/temp/test$ ./fcntl
argv[0]:3, argv[1]:(null)
hello,world~
ret:13
mutian@mutian:~/Downloads/temp/test$ ls
fcntl  fcntl.c  pighead.txt  te.log  test  test.c
mutian@mutian:~/Downloads/temp/test$ cat pighead.txt
hello,world~
mutian@mutian:~/Downloads/temp/test$ cat te.log
abc
mutian@mutian:~/Downloads/temp/test$ rm pighead.txt te.log
mutian@mutian:~/Downloads/temp/test$ vi fcntl.c
//修改代码后
mutian@mutian:~/Downloads/temp/test$ g++ -o fcntl fcntl.c
mutian@mutian:~/Downloads/temp/test$ ./fcntl
argv[0]:3, argv[1]:(null)
hello,world~
ret:-1
mutian@mutian:~/Downloads/temp/test$ ls
fcntl  fcntl.c  pighead.txt  te.log  test  test.c
mutian@mutian:~/Downloads/temp/test$ cat pighead.txt     //由于关闭了fd, 所以这里内容写不进去
mutian@mutian:~/Downloads/temp/test$ cat te.log
abc
mutian@mutian:~/Downloads/temp/test$