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ignore_handler_s set_constraint_handler_s static_assert File input/output clearerr(清除/复位) fclose feof ferror fflush(清空文件缓冲区) fgetc fgetpos fgets fgetwc fgetws File input/output fopen fopen_s fprintf fprintf_s fputc fputs fputwc fputws fread freopen freopen_s fscanf fscanf_s fseek fsetpos ftell fwide fwprintf fwprintf_s fwrite fwscanf fwscanf_s getc getchar gets gets_s getwchar perror printf printf_s putc putchar puts putwc putwchar remove rename rewind scanf scanf_s setbuf setvbuf snprintf sprintf sscanf sscanf_s swprintf swprintf_s swscanf swscanf_s tmpfile tmpfile_s tmpnam tmpnam_s ungetc ungetwc vfprintf vfprintf_s vfscanf vfscanf_s vfwprintf vfwprintf_s vfwscanf vfwscanf_s vprintf vprintf_s vscanf vscanf_s vsnprintf vsprintf vsscanf vsscanf_s vswprintf vswprintf_s vswscanf vswscanf_s vwprintf vwprintf_s vwscanf vwscanf_s wprintf wprintf_s wscanf wscanf_s Localization support lconv LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME localeconv Localization support setlocale 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FE_ALL_EXCEPT FE_DFL_ENV FE_DIVBYZERO FE_DOWNWARD FE_INEXACT FE_INVALID FE_OVERFLOW FE_TONEAREST FE_TOWARDZERO FE_UNDERFLOW FE_UPWARD Floating-point environment float_t floor floorf floorl fma fmaf fmal fmax fmaxf fmaxl fmin fminf fminl fmod fmodf fmodl fpclassify FP_INFINITE FP_NAN FP_NORMAL FP_SUBNORMAL FP_ZERO frexp frexpf frexpl HUGE_VAL HUGE_VALF HUGE_VALL hypot hypotf hypotl I ilogb ilogbf ilogbl imaginary imaxabs imaxdiv INFINITY isfinite isgreater isgreaterequal isinf isless islessequal islessgreater isnan isnormal isunordered labs ldexp ldexpf ldexpl ldiv lgamma lgammaf lgammal llabs lldiv llrint llrintf llrintl llround llroundf llroundl log log10 log10f log10l log1p log1pf log1pl log2 log2f log2l logb logbf logbl logf logl lrint lrintf lrintl lround lroundf lroundl MATH_ERREXCEPT math_errhandling MATH_ERRNO modf modff modfl nan NAN nanf nanl nearbyint nearbyintf nearbyintl nextafter nextafterf nextafterl nexttoward nexttowardf nexttowardl Numerics pow powf powl Pseudo-random number generation rand RAND_MAX remainder remainderf remainderl remquo remquof remquol rint rintf rintl round roundf roundl scalbln scalblnf scalblnl scalbn scalbnf scalbnl signbit sin sinf sinh sinhf sinhl sinl sqrt sqrtf sqrtl srand tan tanf tanh tanhf tanhl tanl tgamma tgammaf tgammal trunc truncf truncl Type-generic math _Complex_I _Imaginary_I Program support abort atexit at_quick_exit exit EXIT_FAILURE EXIT_SUCCESS getenv getenv_s jmp_buf longjmp Program support utilities quick_exit raise setjmp SIGABRT SIGFPE SIGILL SIGINT signal SIGSEGV SIGTERM sig_atomic_t SIG_DFL SIG_ERR SIG_IGN system _Exit Strings atof atoi atol atoll btowc c16rtomb c32rtomb char16_t char32_t isalnum isalpha isblank iscntrl isdigit isgraph islower isprint ispunct isspace isupper iswalnum iswalpha iswblank iswcntrl iswctype iswdigit iswgraph iswlower iswprint iswpunct iswspace iswupper iswxdigit isxdigit mblen mbrlen mbrtoc16 mbrtoc32 mbrtowc mbsinit mbsrtowcs mbsrtowcs_s mbstate_t mbstowcs mbstowcs_s mbtowc memchr memcmp memcpy memcpy_s memmove memmove_s memset memset_s Null-terminated byte strings Null-terminated multibyte strings Null-terminated wide strings strcat strcat_s strchr strcmp strcoll strcpy strcpy_s strcspn strerror strerrorlen_s strerror_s Strings library strlen strncat Thread support call_once cnd_broadcast cnd_destroy cnd_init cnd_signal cnd_timedwait cnd_wait mtx_destroy mtx_init mtx_lock mtx_plain mtx_recursive mtx_timed mtx_timedlock mtx_trylock mtx_unlock once_flag ONCE_FLAG_INIT thrd_busy thrd_create thrd_current thrd_detach thrd_equal thrd_error thrd_exit thrd_join thrd_nomem thrd_sleep thrd_success thrd_timedout thrd_yield Thread support library thread_local tss_create tss_delete TSS_DTOR_ITERATIONS tss_get tss_set Type support Boolean type support library Fixed width integer types FLT_EVAL_METHOD FLT_ROUNDS max_align_t NULL Numeric limits offsetof ptrdiff_t size_t Type support Variadic functions Variadic functions va_arg va_copy va_end va_list va_start
文字

在头文件<stdio.h>中定义




(1)


FILE * freopen(const char * filename,const char * mode,FILE * stream);

(直到C99)


FILE * freopen(const char *限制文件名,const char *限制模式,FILE *限制流);

(自C99以来)


errno_t freopen_s(FILE * restrict * restrict newstreamptr,const char * restrict filename,const char * restrict mode,FILE * restrict stream);

(2)

(自C11以来)

1)首先,试图关闭与之相关的文件stream,忽略任何错误。然后,如果filename不为null,则尝试打开通过filename使用modeas 指定的文件fopen,并将该文件与指向的文件流相关联stream。如果filename是空指针,那么函数将尝试重新打开已经关联的文件stream(在此情况下,它是实现定义允许哪些模式更改)。

2)与(1)相同,不同之处在于mode,处理方式如下,fopen_s指向文件流的指针被写入,newstreamptr并且在运行时检测到以下错误并调用当前安装的约束处理函数:

  • newstreamptr 是一个空指针

  • stream 是一个空指针

  • mode 是一个空指针

作为所有的边界检查函数,freopen_s只能保证__STDC_LIB_EXT1__是由实现定义的,并且如果用户在包含之前定义__STDC_WANT_LIB_EXT1__为整数常量。  1<stdio.h>

参数

文件名

-

将文件流关联到的文件名








































模式

-

用空字符结尾的字符串确定新的文件访问模式文件访问模式字符串含义说明如果文件已存在,则采取措施如果文件不存在,则采取措施“r”读取打开读取文件读取从开始失败读取以打开“w”写入创建文件写入销毁内容创建新的“a”追加附加到文件写入结束创建新的“r +”读取扩展打开文件进行读取/写入从启动错误读取“w +”写入扩展创建文件进行读取/写入销毁内容创建新文件“a +”追加扩展打开一个文件进行读/写写操作结束创建新的文件访问模式标志“b”可以选择指定在二进制模式下打开一个文件。该标志只对Windows系统有效。在附加文件访问模式下,无论文件位置指示符的当前位置如何,数据都会写入文件末尾。当以更新模式('+'作为上述模式参数值列表中的第二个或第三个字符)打开文件时,可以在关联的流上执行输入和输出。然而,输出不应直接跟随输入,而不需要对fflush函数或文件定位函数(fseek,fsetpos或rewind)进行干预调用,并且输入不应直接跟随输出,而不需要中间调用文件定位函数,除非输入操作遇到文件结束。在某些实现中打开(或创建)具有更新模式的文本文件可能会打开(或创建)二进制流。文件访问模式标志“x” 可以选择性地附加到“w”或“w +”说明符。如果文件存在,该标志强制该功能失败,而不是覆盖它。(C11)使用fopen_s或freopen_s时,用“w”或“a”创建的任何文件的文件访问权限会阻止其他用户访问它。文件访问模式标志“u”可以有选择地添加到以“w”或“a”开头的任何说明符中,以启用默认的fopen权限。(C11)可以有选择地添加到以“w”或“a”开头的任何说明符中,以启用默认的fopen权限。(C11)可以有选择地添加到以“w”或“a”开头的任何说明符中,以启用默认的fopen权限。(C11)

File access mode string

Meaning

Explanation

Action if file  already exists

Action if file  does not exist

"r"

read

Open a file for reading

read from start

failure to open

"w"

write

Create a file for writing

destroy contents

create new

"a"

append

Append to a file

write to end

create new

"r+"

read extended

Open a file for read/write

read from start

error

"w+"

write extended

Create a file for read/write

destroy contents

create new

"a+"

append extended

Open a file for read/write

write to end

create new

File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has effect only on Windows systems.  On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.

When a file is opened with update mode ('+' as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end- of-file. Opening (or creating) a text file with update mode may instead open (or create) a binary stream in some implementations.

File access mode flag "x" can optionally be appended to "w" or "w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it. (C11)

当使用fopen_s或freopen_s时,用“w”或“a”创建的任何文件的文件访问权限会阻止其他用户访问它。文件访问模式标志“u”可以有选择地添加到以“w”或“a”开头的任何说明符中,以启用默认的fopen权限。(C11)

文件访问模式字符串

含义

说明

行动如果文件已经存在

如果文件不存在,则采取行动






































“R”

打开一个文件以供阅读

从开始阅读

未能打开






































“W”

创建一个文件写入

破坏内容

创建新的






































“一个”

附加

附加到文件

写入结束

创建新的






































“R +”

阅读扩展

打开文件进行读取/写入

从开始阅读

错误






































“W +”

写入扩展

创建一个用于读/写的文件

破坏内容

创建新的






































“A +”

追加扩展

打开文件进行读取/写入

写入结束

创建新的






































返回值

1)stream成功的值的副本,失败时的空指针。

2)成功时为零(并且stream写入的值的副本,*newstreamptr错误时不为零(并且空指针被写入,*newstreamptr除非newstreamptr它本身是空指针)。

注意

freopen是通过I / O操作或通过I / O操作建立后,改变流的窄/宽方向的唯一方法fwide

Example

以下代码重定向stdout到一个文件。

#include <stdio.h>#include <stdlib.h>
 int main(void){    puts("stdout is printed to console");    if (freopen("redir.txt", "w", stdout) == NULL)    {       perror("freopen() failed");       return EXIT_FAILURE;    }    puts("stdout is redirected to a file"); // this is written to redir.txt    fclose(stdout);}

输出:

stdout is printed to console

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.21.5.4 freopen函数(p:307)

    • K.3.5.2.2 freopen_s函数(p:590)

  • C99标准(ISO / IEC 9899:1999):

    • 7.19.5.4 freopen函数(p:272-273)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.9.5.4 freopen函数

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