复制文件失败,EBADF关闭输出文件描述符

时间:2016-07-22 09:37:47

标签: c linux linux-kernel system-calls

所以我正在阅读一本有点过时的书(2010),我试图用Linux系统调用复制一个文件。这就是我所拥有的:

注意:忽略tlpi_hdr.herror_functions.h,他们定义errExit()fatal()以及其他一些,他们只是打印错误并退出。

#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;
}

我未能使用EBADF Bad file descriptor关闭输出文件描述符:

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

文件副本很好:

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

为什么?

1 个答案:

答案 0 :(得分:3)

让我们仔细看看您的close电话:

close(outputFd == -1)

您要将outputFd与值-1进行比较。结果是布尔值,在C中将是01。这恰好是标准输入或标准输出,具体取决于结果。不是您应该关闭的描述文件。

我的猜测是你的意思

if (close(outputFd) == -1)