freopen、_wfreopenfreopen, _wfreopen

重新分配文件指针。Reassigns a file pointer. 提供这些函数的更安全版本;请参阅 freopen_s、_wfreopen_sMore secure versions of these functions are available; see freopen_s, _wfreopen_s.


FILE *freopen(
   const char *path,
   const char *mode,
   FILE *stream
FILE *_wfreopen(
   const wchar_t *path,
   const wchar_t *mode,
   FILE *stream


新文件的路径。Path of new file.

允许的访问类型。Type of access permitted.

指向文件结构的指针。Pointer to FILE structure.

返回值Return Value

这些函数均返回指向新打开的文件的指针。Each of these functions returns a pointer to the newly opened file. 如果发生错误,则关闭原始文件,该函数将返回NULL指针值。If an error occurs, the original file is closed and the function returns a NULL pointer value. 如果路径模式,或是 null 指针,或如果filename为空字符串,这些函数将调用无效的参数处理程序,如中所述参数验证If path, mode, or stream is a null pointer, or if filename is an empty string, these functions invoke the invalid parameter handler, as described in Parameter Validation. 如果允许执行继续,则这些函数将设置errnoEINVAL并返回NULLIf execution is allowed to continue, these functions set errno to EINVAL and return NULL.

有关这些代码以及其他错误代码的详细信息,请参阅 _doserrno、errno、_sys_errlist 和 _sys_nerrSee _doserrno, errno, _sys_errlist, and _sys_nerr for more information on these, and other, error codes.


提供这些函数的更安全版本;请参阅 freopen_s、_wfreopen_sMore secure versions of these functions exist, see freopen_s, _wfreopen_s.

Freopen函数关闭当前与关联的文件,并重新指定到指定的文件路径The freopen function closes the file currently associated with stream and reassigns stream to the file specified by path. _wfreopen是宽字符版本的 _freopen;路径模式自变量 _wfreopen是宽字符字符串。_wfreopen is a wide-character version of _freopen; the path and mode arguments to _wfreopen are wide-character strings. _wfreopen_freopen否则具有相同行为。_wfreopen and _freopen behave identically otherwise.

一般文本例程映射Generic-Text Routine Mappings

TCHAR.H 例程TCHAR.H routine 未定义 _UNICODE 和 _MBCS_UNICODE & _MBCS not defined 已定义 _MBCS_MBCS defined 已定义 _UNICODE_UNICODE defined
_tfreopen_tfreopen freopenfreopen freopenfreopen _wfreopen_wfreopen

freopen通常用于将预先打开的文件重定向stdinstdout,和stderr到指定的用户文件。freopen is typically used to redirect the pre-opened files stdin, stdout, and stderr to files specified by the user. 与关联的新文件使用打开模式,后者是一个字符串,指定,如下所示为该文件,请求的访问类型:The new file associated with stream is opened with mode, which is a character string specifying the type of access requested for the file, as follows:

模式mode AccessAccess
“r”"r" 打开以便读取。Opens for reading. 如果文件不存在或找不到freopen调用将失败。If the file does not exist or cannot be found, the freopen call fails.
“w”"w" 打开用于写入的空文件。Opens an empty file for writing. 如果给定文件存在,则其内容会被销毁。If the given file exists, its contents are destroyed.
“a”"a" 在文件末尾打开以进行写入(追加),在新数据写入到文件之前不移除文件末尾 (EOF) 标记。Opens for writing at the end of the file (appending) without removing the end-of-file (EOF) marker before new data is written to the file. 创建文件(如果文件不存在)。Creates the file if it does not exist.
“r+”"r+" 打开以便读取和写入。Opens for both reading and writing. 文件必须存在。The file must exist.
“w+”"w+" 打开用于读取和写入的空文件。Opens an empty file for both reading and writing. 如果文件存在,则其内容会被销毁。If the file exists, its contents are destroyed.
“a+”"a+" 打开以进行读取和追加。Opens for reading and appending. 追加操作包括在新数据写入文件之前移除 EOF 标记。The appending operation includes the removal of the EOF marker before new data is written to the file. 写入完成后,EOF 标记不会还原。The EOF marker is not restored after writing is completed. 创建文件(如果文件不存在)。Creates the file if it does not exist.

使用 "w""w +" 类型时要小心,因为它们可能会销毁现有文件。Use the "w" and "w+" types with care, as they can destroy existing files.

当用打开文件时 "a""a +" 访问类型,所有写入操作均将在文件末尾。When a file is opened with the "a" or "a+" access type, all write operations take place at the end of the file. 尽管可以使用重新定位文件指针fseekrewind,文件指针将始终被移回文件末尾到任何写入操作执行前。因此,无法覆盖现有数据。Although the file pointer can be repositioned using fseek or rewind, the file pointer is always moved back to the end of the file before any write operation is carried out. Thus, existing data cannot be overwritten.

"A" 模式不会追加到文件之前删除 EOF 标记。The "a" mode does not remove the EOF marker before appending to the file. 在追加后,MS-DOS TYPE 命令只显示原始 EOF 标记之前的数据,不显示追加到文件的任何数据。After appending has occurred, the MS-DOS TYPE command only shows data up to the original EOF marker and not any data appended to the file. "A +" 模式未追加到文件之前移除 EOF 标记。The "a+" mode does remove the EOF marker before appending to the file. 在追加后,MS-DOS TYPE 命令显示文件中的所有数据。After appending, the MS-DOS TYPE command shows all data in the file. "A +" 模式则需要才能附加到通过 CTRL + Z EOF 标记终止的流文件。The "a+" mode is required for appending to a stream file that is terminated with the CTRL+Z EOF marker.

"r +""w +",或 "a +" 指定访问类型,允许读取和写入 (文件将状态才能打开进行"更新")。When the "r+", "w+", or "a+" access type is specified, both reading and writing are allowed (the file is said to be open for "update"). 但是,在读取与写入之间切换时,必须有干预性的 fsetposfseekrewind 操作。However, when you switch between reading and writing, there must be an intervening fsetpos, fseek, or rewind operation. 可以为指定当前位置fsetposfseek操作,如果所需的。The current position can be specified for the fsetpos or fseek operation, if desired. 除了以上值,以下字符之一可能包括在模式字符串,以指定换行符的转换模式。In addition to the above values, one of the following characters may be included in the mode string to specify the translation mode for new lines.

模式修饰符mode modifier 转换模式Translation mode
tt 在文本(转换)模式下打开。Open in text (translated) mode.
bb 在二进制(未转换)模式下打开;不进行涉及回车和换行字符的转换。Open in binary (untranslated) mode; translations involving carriage-return and linefeed characters are suppressed.

在文本 (转换) 模式下,回车换行符 (CR-LF) 组合将转换为单一的换行 (LF) 字符输入;LF 字符将转换为 CR-LF 组合输出。In text (translated) mode, carriage return-linefeed (CR-LF) combinations are translated into single linefeed (LF) characters on input; LF characters are translated to CR-LF combinations on output. CTRL+Z 也将在输入时解释为文件尾字符。Also, CTRL+Z is interpreted as an end-of-file character on input. 在打开的文件进行读取或写入和读取与 "a +",运行时库检查文件末尾的 CTRL + Z 并移除它,如有可能。In files opened for reading or for writing and reading with "a+", the run-time library checks for a CTRL+Z at the end of the file and removes it, if possible. 这样做是因为使用fseekftell在文件内移动可能会导致fseek文件末尾附近运行不当。This is done because using fseek and ftell to move within a file may cause fseek to behave improperly near the end of the file. T选项是一个 Microsoft 扩展,不应需要 ANSI 可移植性时使用。The t option is a Microsoft extension that should not be used where ANSI portability is desired.

如果tb中未给定模式,则默认转换模式由全局变量_fmodeIf t or b is not given in mode, the default translation mode is defined by the global variable _fmode. 如果tb将作为自变量,函数将失败并返回前缀NULLIf t or b is prefixed to the argument, the function fails and returns NULL.

有关文本模式和二进制模式的讨论,请参阅文本和二进制模式文件 I/OFor a discussion of text and binary modes, see Text and Binary Mode File I/O.


函数Function 必需的标头Required header
freopenfreopen <stdio.h><stdio.h>
_wfreopen_wfreopen <stdio.h> 或 <wchar.h><stdio.h> or <wchar.h>

通用 Windows 平台 (UWP) 应用中不支持控制台。The console is not supported in Universal Windows Platform (UWP) apps. 控制台中,与关联的标准流句柄stdinstdout,和stderr,必须将 C 运行时函数才能使用它们在 UWP 应用重定向.The standard stream handles that are associated with the console, stdin, stdout, and stderr, must be redirected before C run-time functions can use them in UWP apps. 有关其他兼容性信息,请参阅 兼容性For additional compatibility information, see Compatibility.


// crt_freopen.c
// compile with: /W3
// This program reassigns stderr to the file
// named FREOPEN.OUT and writes a line to that file.
#include <stdio.h>
#include <stdlib.h>

FILE *stream;

int main( void )
   // Reassign "stderr" to "freopen.out":
   stream = freopen( "freopen.out", "w", stderr ); // C4996
   // Note: freopen is deprecated; consider using freopen_s instead

   if( stream == NULL )
      fprintf( stdout, "error on freopen\n" );
      fprintf( stdout, "successfully reassigned\n" ); fflush( stdout );
      fprintf( stream, "This will go to the file 'freopen.out'\n" );
      fclose( stream );
   system( "type freopen.out" );
successfully reassigned
This will go to the file 'freopen.out'

请参阅See also

流 I/OStream I/O
fclose、_fcloseallfclose, _fcloseall
_fdopen、_wfdopen_fdopen, _wfdopen
fopen、_wfopen_wfopenfopen, _wfopen
_open、_wopen_open, _wopen