复制文件失败，关闭输出文件描述符时EBADF

Question

So I was following a little outdated book (2010) and I'm trying to copy a file with Linux system calls. This is what i have:

NOTE: Ignore the tlpi_hdr.h and error_functions.h , they define errExit() and fatal() and some otheres, they just print the error and exit.

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

#include "lib/tlpi_hdr.h"
#include "lib/error_functions.h"

#ifndef BUF_SIZE
#define BUF_SIZE 1024
#endif

int main(int argc, char *argv[])
{
    int inputFd, outputFd, openFlags;
    mode_t filePerms;
    ssize_t numRead;
    char buf[BUF_SIZE];

    if (argc != 3 || strcmp(argv[1], "--help") == 0) {
        usageErr("%s old-file new-file\n", argv[0]);
    }

    inputFd = open(argv[1], O_RDONLY);

    if (inputFd == -1) {
        errExit("Opening file %s", argv[1]);
    }

    openFlags = O_CREAT | O_WRONLY | O_TRUNC;
    filePerms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;

    outputFd = open(argv[2], openFlags, filePerms);

    if (outputFd == -1) {
        errExit("Opening file for writing %s", argv[1]);
    }

    while ((numRead = read(inputFd, buf, BUF_SIZE)) > 0) {

        if (write(outputFd, buf, numRead) != numRead))
            fatal("I/O Error");

        if (numRead == -1)
            fatal("Reading error");

    }

    if (close(outputFd == -1))
        errExit("close input");
    if (close(inputFd == -1))
        errExit("close output");

    return EXIT_SUCCESS;
}

I'm failing on closing of the output file descriptor with EBADF Bad file descriptor :

thinkpad :: ~/.tlpi % ./cp.o a b                                                                                                                                                 
ERROR [EBADF Bad file descriptor] close output

The file copies fine tho:

thinkpad :: ~/.tlpi % sha1sum a                                                                                                                                   
40a925a93e149ac53d2630cde8adeb63b8134b29  a
thinkpad :: ~/.tlpi % sha1sum b                                                                                                                                                  
40a925a93e149ac53d2630cde8adeb63b8134b29  b
thinkpad :: ~/.tlpi %

Why?

Answer 1

Let's take a closer look at your close call:

close(outputFd == -1)

Here you are comparing outputFd to the value -1 . The result of that is a boolean value, which in C will be either 0 or 1 . This happens to be either standard input or standard output, depending on the result. Not a file you descriptor you should close.

My guess is that you meant

if (close(outputFd) == -1)