c_cpp 一个小程序，显示在shell中指定它时，您实际上可以写入0/1/2以外的不同文件描述符！

Posted 2021-05-14

#include <stdio.h>

const int CUSTOM_FILENO = 3;

// run the program in the shell like "./extra-fd 3>out"
// it writes a line to the file "out"

int main() {
    FILE* file = fdopen(CUSTOM_FILENO, "w");

    if (file == NULL) {
        char buf[48];
        sprintf(buf, "cannot output to fd=%d", CUSTOM_FILENO);
        perror(buf);
        return 1;
    }

    fputs("Hello, world!\n", file);
    fclose(file);

    fprintf(stderr, "successfully write to fd=%d\n", CUSTOM_FILENO);
}