linux编程fcntl获取和设置文件状态

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

#define ERR_EXIT( m ) 
        do 
        { 
                perror( m ); 
                exit( EXIT_FAILURE ); 
        }while( 0 )

//设置某个文件状态
void set_flag( int fd, int flags );
//清除某个文件状态
void clear_flag( int fd, int flags );

int main( int argc, char* argv[] ) {

        char buf[64] = { 0 };
        int nread;

        //设置非阻塞状态
        set_flag( 0, O_NONBLOCK );
        //清除非阻塞状态, 读取标准输入又变成阻塞
        clear_flag( 0, O_NONBLOCK );
        nread = read( 0, buf, 64 );
        if( -1 == nread ) {
                ERR_EXIT( "获取输入失败" );
        }
        printf( "buf=%s
", buf );

        return 0;
}

void set_flag( int fd, int flags ) {
        int oldflag;
        oldflag = fcntl( fd, F_GETFL, 0 );
        if( -1 == oldflag ) {
                ERR_EXIT( "获取原来的状态失败" );
        }

        oldflag = oldflag | flags;
        int ret = fcntl( fd, F_SETFL, oldflag );
        if( -1 == ret ) {
                ERR_EXIT( "设置新的文件状态失败" );
        }
}

void clear_flag( int fd, int flags ) {
        int oldflag;
        oldflag = fcntl( fd, F_GETFL, 0 );
        if( -1 == oldflag ) {
                ERR_EXIT( "获取原来的状态失败" );
        }
        oldflag = oldflag & ~flags;
        int ret = fcntl( fd, F_SETFL, oldflag );
        if( -1 == ret ) {
                ERR_EXIT( "设置新的文件状态失败" );
        }
}