linux編程fcntl獲取和設置文件狀態

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

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

//設置某個文件狀態
void set_flag( int fd, int flags );
//清除某個文件狀態
void clear_flag( int fd, int flags );

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

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

        //設置非阻塞狀態
        set_flag( 0, O_NONBLOCK );
        //清除非阻塞狀態, 讀取標準輸入又變成阻塞
        clear_flag( 0, O_NONBLOCK );
        nread = read( 0, buf, 64 );
        if( -1 == nread ) {
                ERR_EXIT( "獲取輸入失敗" );
        }
        printf( "buf=%s\n", buf );

        return 0;
}

void set_flag( int fd, int flags ) {
        int oldflag;
        oldflag = fcntl( fd, F_GETFL, 0 );
        if( -1 == oldflag ) {
                ERR_EXIT( "獲取原來的狀態失敗" );
        }

        oldflag = oldflag | flags;
        int ret = fcntl( fd, F_SETFL, oldflag );
        if( -1 == ret ) {
                ERR_EXIT( "設置新的文件狀態失敗" );
        }
}

void clear_flag( int fd, int flags ) {
        int oldflag;
        oldflag = fcntl( fd, F_GETFL, 0 );
        if( -1 == oldflag ) {
                ERR_EXIT( "獲取原來的狀態失敗" );
        }
        oldflag = oldflag & ~flags;
        int ret = fcntl( fd, F_SETFL, oldflag );
        if( -1 == ret ) {
                ERR_EXIT( "設置新的文件狀態失敗" );
        }
}