fcntl即F_SETFL,F_GETFL的使用，設置文件的flags

1、獲取文件的flags，即open函數的第二個參數:

       flags = fcntl(fd,F_GETFL,0);

2、設置文件的flags:

      fcntl(fd,F_SETFL,flags);

3、增加文件的某個flags，比如文件是阻塞的，想設置成非阻塞:

       flags = fcntl(fd,F_GETFL,0);

       flags |= O_NONBLOCK;

      fcntl(fd,F_SETFL,flags);

4、取消文件的某個flags，比如文件是非阻塞的，想設置成爲阻塞:

      flags = fcntl(fd,F_GETFL,0);

      flags &= ~O_NONBLOCK;

      fcntl(fd,F_SETFL,flags);

 

 

獲取和設置文件flags舉例::

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <error.h>

char buf[500000];

int main(int argc,char *argv[])
{
        int ntowrite,nwrite;
        const char *ptr ;
        int flags;
   
        ntowrite = read(STDIN_FILENO,buf,sizeof(buf));
        if(ntowrite <0)
        {  
                perror("read STDIN_FILENO fail:");
                exit(1);
        }  
        fprintf(stderr,"read %d bytes\n",ntowrite);
   
        if((flags = fcntl(STDOUT_FILENO,F_GETFL,0))==-1)
        {  
                perror("fcntl F_GETFL fail:");
                exit(1);
        }  
        flags |= O_NONBLOCK;
        if(fcntl(STDOUT_FILENO,F_SETFL,flags)==-1)
        {  
                perror("fcntl F_SETFL fail:");
                exit(1);
        }  
   
        ptr = buf;
        while(ntowrite > 0)
        {  
                nwrite = write(STDOUT_FILENO,ptr,ntowrite);
                if(nwrite == -1)
                {  

                        perror("write file fail:");
                }  
                if(nwrite > 0)
                {  
                        ptr += nwrite;
                        ntowrite -= nwrite;
                }  
        }  
   
        flags &= ~O_NONBLOCK;
        if(fcntl(STDOUT_FILENO,F_SETFL,flags)==-1)
        {  
                perror("fcntl F_SETFL fail2:");
        }  
        return 0;