量化交易之linux篇 - 《UNIX环境高级编程》 - 指定文件描述符，并对于该描述符打印其所选择的文件标志说明

#include "apue.h"
#include <stdio.h>
#include <fcntl.h>

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

    if (argc != 2)
        err_quit("error quit.");

    if ((val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
        err_sys("fcntl error for id: %d", atoi(argv[1]));

    switch(val & O_ACCMODE) {
        case O_RDONLY:
            printf("read only.\n");
            break;
        case O_WRONLY:
            printf("write only.\n");
            break;
        case O_RDWR:
            printf("read write.\n");
        default:
            err_dump("unknow access mode.");
    }

    if (val & O_APPEND) {
        printf(", append\n");
    }

    if (val & O_NONBLOCK) {
        printf(", non block\n");
    }

    if (val & O_SYNC) {
        printf(", synchronours writes \n");
    }

#if !defined(_POXIX_C_SOURCE) && defined(O_FSYNC) && (O_FSYNC != O_SYNC)
    if (val & O_SYNC) {
        printf(", synchronours writes\n");
    }
#endif

    putchar('\n');

    exit(0);
}