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Algorithms Algorithms(算法) bsearch bsearch_s qsort qsort_s Atomic operations Atomic operations library(原子操作庫(kù)) ATOMIC_*_LOCK_FREE atomic_compare_exchange_strong atomic_compare_exchange_strong_explicit atomic_compare_exchange_weak atomic_compare_exchange_weak_explicit atomic_exchange atomic_exchange_explicit atomic_fetch_add atomic_fetch_add_explicit atomic_fetch_and atomic_fetch_and_explicit atomic_fetch_or atomic_fetch_or_explicit atomic_fetch_sub atomic_fetch_sub_explicit atomic_fetch_xor atomic_fetch_xor_explicit atomic_flag atomic_flag_clear atomic_flag_clear_explicit ATOMIC_FLAG_INIT atomic_flag_test_and_set atomic_flag_test_and_set_explicit atomic_init atomic_is_lock_free atomic_load atomic_load_explicit atomic_signal_fence atomic_store atomic_store_explicit atomic_thread_fence(線程圍欄) ATOMIC_VAR_INIT kill_dependency memory_order(內(nèi)存排序) C keywords auto(自動(dòng)存儲(chǔ)) break(跳出循環(huán)) C keywords(關(guān)鍵詞) case char const(常量修飾符) continue default(預(yù)設(shè)運(yùn)算式) do 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language C Operator Precedence cast operator character constant(字符字面量) Comments(注釋符) Comparison operators(比較運(yùn)算符) compound literals(符合字面量) Conditional inclusion(條件包含) Conformance(一致性) const type qualifier(const 限定符) Constant expressions(常量表達(dá)) continue statement Declarations(聲明) do-while loop Enumerations(枚舉類型) Escape sequences(轉(zhuǎn)義字符) Expressions(表達(dá)式) External and tentative definitions(外部和暫定的定義) File scope(文件范圍) floating constant(浮點(diǎn)常量) for loop Function declarations(函數(shù)聲明) Function definitions(函數(shù)聲明) Functions Generic selection泛型選擇 goto statement Identifier(標(biāo)示符) if statement Implicit conversions(隱式轉(zhuǎn)換) Increment/decrement operators(前置/后置操作符) Initialization(初始化) inline function specifier(內(nèi)聯(lián)函式) integer constant Lifetime(生命期) Logical operators(邏輯運(yùn)算符) Lookup and name spaces Main function(主函式) Member access operators(會(huì)員接入運(yùn)營(yíng)商) Memory model Objects and alignment(字節(jié)對(duì)齊) Order of evaluation(評(píng)估順序) Other 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localtime_s mktime(將時(shí)間結(jié)構(gòu)數(shù)據(jù)轉(zhuǎn)換成經(jīng)過(guò)的秒數(shù)的函數(shù)) strftime(格式化輸出時(shí)間函數(shù)) time timespec timespec_get time_t tm wcsftime(格式化時(shí)間寬字符) Dynamic memory management aligned_alloc C memory management library(內(nèi)存管理庫(kù)) calloc free(釋放動(dòng)態(tài)分配空間的函數(shù)) malloc(動(dòng)態(tài)分配內(nèi)存空間的函數(shù)) realloc(重新分配內(nèi)存空間的函數(shù)) Error handling abort_handler_s assert(斷言) constraint_handler_t errno(錯(cuò)誤報(bào)告) Error handling(錯(cuò)誤處理) Error numbers(錯(cuò)誤個(gè)數(shù)) ignore_handler_s set_constraint_handler_s static_assert File input/output clearerr(清除/復(fù)位) fclose feof ferror fflush(清空文件緩沖區(qū)) 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 Numerics abs acos acosf acosh acoshf acoshl acosl asin asinf asinh asinhf asinhl asinl atan atan2 atan2f atan2l atanf atanh atanhf atanhl atanl cabs cabsf cabsl cacos cacosf cacosh cacoshf cacoshl cacosl carg cargf cargl casin casinf casinh casinhf casinhl casinl catan catanf catanh catanhf catanhl catanl cbrt cbrtf cbrtl ccos ccosf ccosh ccoshf ccoshl ccosl ceil ceilf ceill cexp cexpf cexpl cimag cimagf cimagl clog clogf clogl CMPLX CMPLXF CMPLXL Common mathematical functions complex Complex number arithmetic conj conjf conjl copysign copysignf copysignl cos cosf cosh coshf coshl cosl cpow cpowf cpowl cproj cprojf cprojl creal crealf creall csin csinf csinh csinhf csinhl csinl csqrt csqrtf csqrtl ctan ctanf ctanh ctanhf ctanhl ctanl div double_t erf erfc erfcf erfcl erff erfl exp exp2 exp2f exp2l expf expl expm1 expm1f expm1l fabs fabsf fabsl fdim feclearexcept fegetenv fegetexceptflag fegetround feholdexcept feraiseexcept fesetenv fesetexceptflag fesetround fetestexcept feupdateenv 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
characters

在頭文件<stdio.h>中定義




(1)


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

(直到C99)


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

(自C99以來(lái))


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

(2)

(自C11以來(lái))

1)首先,試圖關(guān)閉與之相關(guān)的文件stream,忽略任何錯(cuò)誤。然后,如果filename不為null,則嘗試打開通過(guò)filename使用modeas 指定的文件fopen,并將該文件與指向的文件流相關(guān)聯(lián)stream。如果filename是空指針,那么函數(shù)將嘗試重新打開已經(jīng)關(guān)聯(lián)的文件stream(在此情況下,它是實(shí)現(xiàn)定義允許哪些模式更改)。

2)與(1)相同,不同之處在于mode,處理方式如下,fopen_s指向文件流的指針被寫入,newstreamptr并且在運(yùn)行時(shí)檢測(cè)到以下錯(cuò)誤并調(diào)用當(dāng)前安裝的約束處理函數(shù):

  • newstreamptr 是一個(gè)空指針

  • stream 是一個(gè)空指針

  • mode 是一個(gè)空指針

作為所有的邊界檢查函數(shù),freopen_s只能保證__STDC_LIB_EXT1__是由實(shí)現(xiàn)定義的,并且如果用戶在包含之前定義__STDC_WANT_LIB_EXT1__為整數(shù)常量。  1<stdio.h>

參數(shù)

文件名

-

將文件流關(guān)聯(lián)到的文件名








































模式

-

用空字符結(jié)尾的字符串確定新的文件訪問(wèn)模式文件訪問(wèn)模式字符串含義說(shuō)明如果文件已存在,則采取措施如果文件不存在,則采取措施“r”讀取打開讀取文件讀取從開始失敗讀取以打開“w”寫入創(chuàng)建文件寫入銷毀內(nèi)容創(chuàng)建新的“a”追加附加到文件寫入結(jié)束創(chuàng)建新的“r +”讀取擴(kuò)展打開文件進(jìn)行讀取/寫入從啟動(dòng)錯(cuò)誤讀取“w +”寫入擴(kuò)展創(chuàng)建文件進(jìn)行讀取/寫入銷毀內(nèi)容創(chuàng)建新文件“a +”追加擴(kuò)展打開一個(gè)文件進(jìn)行讀/寫寫操作結(jié)束創(chuàng)建新的文件訪問(wèn)模式標(biāo)志“b”可以選擇指定在二進(jìn)制模式下打開一個(gè)文件。該標(biāo)志只對(duì)Windows系統(tǒng)有效。在附加文件訪問(wèn)模式下,無(wú)論文件位置指示符的當(dāng)前位置如何,數(shù)據(jù)都會(huì)寫入文件末尾。當(dāng)以更新模式('+'作為上述模式參數(shù)值列表中的第二個(gè)或第三個(gè)字符)打開文件時(shí),可以在關(guān)聯(lián)的流上執(zhí)行輸入和輸出。然而,輸出不應(yīng)直接跟隨輸入,而不需要對(duì)fflush函數(shù)或文件定位函數(shù)(fseek,fsetpos或rewind)進(jìn)行干預(yù)調(diào)用,并且輸入不應(yīng)直接跟隨輸出,而不需要中間調(diào)用文件定位函數(shù),除非輸入操作遇到文件結(jié)束。在某些實(shí)現(xiàn)中打開(或創(chuàng)建)具有更新模式的文本文件可能會(huì)打開(或創(chuàng)建)二進(jìn)制流。文件訪問(wèn)模式標(biāo)志“x” 可以選擇性地附加到“w”或“w +”說(shuō)明符。如果文件存在,該標(biāo)志強(qiáng)制該功能失敗,而不是覆蓋它。(C11)使用fopen_s或freopen_s時(shí),用“w”或“a”創(chuàng)建的任何文件的文件訪問(wèn)權(quán)限會(huì)阻止其他用戶訪問(wèn)它。文件訪問(wèn)模式標(biāo)志“u”可以有選擇地添加到以“w”或“a”開頭的任何說(shuō)明符中,以啟用默認(rèn)的fopen權(quán)限。(C11)可以有選擇地添加到以“w”或“a”開頭的任何說(shuō)明符中,以啟用默認(rèn)的fopen權(quán)限。(C11)可以有選擇地添加到以“w”或“a”開頭的任何說(shuō)明符中,以啟用默認(rèn)的fopen權(quán)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)

當(dāng)使用fopen_s或freopen_s時(shí),用“w”或“a”創(chuàng)建的任何文件的文件訪問(wèn)權(quán)限會(huì)阻止其他用戶訪問(wèn)它。文件訪問(wèn)模式標(biāo)志“u”可以有選擇地添加到以“w”或“a”開頭的任何說(shuō)明符中,以啟用默認(rèn)的fopen權(quán)限。(C11)

文件訪問(wèn)模式字符串

含義

說(shuō)明

行動(dòng)如果文件已經(jīng)存在

如果文件不存在,則采取行動(dòng)






































“R”

打開一個(gè)文件以供閱讀

從開始閱讀

未能打開






































“W”

創(chuàng)建一個(gè)文件寫入

破壞內(nèi)容

創(chuàng)建新的






































“一個(gè)”

附加

附加到文件

寫入結(jié)束

創(chuàng)建新的






































“R +”

閱讀擴(kuò)展

打開文件進(jìn)行讀取/寫入

從開始閱讀

錯(cuò)誤






































“W +”

寫入擴(kuò)展

創(chuàng)建一個(gè)用于讀/寫的文件

破壞內(nèi)容

創(chuàng)建新的






































“A +”

追加擴(kuò)展

打開文件進(jìn)行讀取/寫入

寫入結(jié)束

創(chuàng)建新的






































返回值

1)stream成功的值的副本,失敗時(shí)的空指針。

2)成功時(shí)為零(并且stream寫入的值的副本,*newstreamptr錯(cuò)誤時(shí)不為零(并且空指針被寫入,*newstreamptr除非newstreamptr它本身是空指針)。

注意

freopen是通過(guò)I / O操作或通過(guò)I / O操作建立后,改變流的窄/寬方向的唯一方法fwide。

Example

以下代碼重定向stdout到一個(gè)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);}

輸出:

stdout is printed to console

參考

  • C11標(biāo)準(zhǔn)(ISO / IEC 9899:2011):

    • 7.21.5.4 freopen函數(shù)(p:307)

    • K.3.5.2.2 freopen_s函數(shù)(p:590)

  • C99標(biāo)準(zhǔn)(ISO / IEC 9899:1999):

    • 7.19.5.4 freopen函數(shù)(p:272-273)

  • C89 / C90標(biāo)準(zhǔn)(ISO / IEC 9899:1990):

    • 4.9.5.4 freopen函數(shù)

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