c - 在c中使用lseek命令获取文件大小

Question

我被要求使用 usjng lseek 命令(不使用 stat)查找文件的大小，我编写了以下代码

int main()
{
    字符 buf[100], fn[10];
    int fd，我；
    printf("请输入文件名\n");
        scanf("%s", fn);
    fd = open(fn, O_RDONLY);
    int size = lseek(fd, 0, SEEK_END);
    printf("大小为 %d", size);
    关闭(fd)；
}

但是我得到的文件大小是-1，我哪里出错了

Answer 1

来自 lseek 文档可用 online :

RETURN VALUE        
Upon successful completion, lseek() returns the resulting offset location as measured in bytes from the beginning of the file. On error, the value (off_t) -1 is returned and errno is set to indicate the error.

所以你必须检查 errno(如果 lseek 返回 -1 则打印它):

来自同一 link 的可能错误列表:

ERRORS

   EBADF  fd is not an open file descriptor.  
   EINVAL whence is not valid.  Or: the resulting file offset would be
          negative, or beyond the end of a seekable device.  
   ENXIO  whence is SEEK_DATA or SEEK_HOLE, and the file offset is
          beyond the end of the file.  
   EOVERFLOW  The resulting file offset cannot be represented in an off_t.  
   ESPIPE fd is associated with a pipe, socket, or FIFO.  

在您的情况下，很可能是 EBADF。