如何在C中的文件描述符中打印信息

Question

(gdb) print* data_out_file[0]
$1 = {_flags = -1, _IO_read_ptr = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_read_end = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_read_base = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_write_base = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_write_ptr = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_write_end = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_buf_base = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_buf_end = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_save_base = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_backup_base = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, 
  _IO_save_end = 0xffffffffffffffff <Address 0xffffffffffffffff out of bounds>, _markers = 0xffffffffffffffff, _chain = 0x11004147ffffffff, 
  _fileno = 498074112, _flags2 = 12648704, _old_offset = 135392766359363840, _cur_column = 240, _vtable_offset = 66 'B', _shortbuf = "á", 
  _lock = 0xecfc392019202004, _offset = -35, __pad1 = 0xffffffffffffffff, __pad2 = 0xffffffffffffffff, __pad3 = 0xffffffffffffffff, 
  __pad4 = 0xffffffffffffffff, __pad5 = 18446744073709551615, _mode = -1, _unused2 = 'ÿ' <repeats 20 times>}

在GDB中，如果我们打印文件指针，我们将获得描述符。 只是想知道我们如何在像printf这样的C代码中做到这一点？

Answer 1

假设您想要与有效的FILE *流对象相关联的int 文件描述符值，请使用fileno()函数 ：

名称

fileno-将流指针映射到文件描述符

概要

 #include <stdio.h> int fileno(FILE *stream); 

描述

该fileno()函数将返回与关联的整文件描述符stream通过指向stream 。

返回值

成功完成后， fileno()将返回与stream关联的文件描述符的整数值。 否则，应返回值-1并errno以指示错误。

您不取消引用FILE *流对象本身。 这样做会导致易碎，不可移植的代码容易损坏。 在某些实现中，根本无法取消引用FILE *结构。