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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 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 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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

int fseek(FILE * stream,long offset,int origin);

将文件流的文件位置指示符设置为stream指向的值offset

如果stream以二进制模式打开,则新位置是offset从文件开始处测量的字节(如果origin是)SEEK_SET,从当前文件位置(如果origin是)SEEK_CUR,以及从文件结尾(如果origin是)开始SEEK_END。二进制流不需要支持SEEK_END,特别是如果输出额外的空字节。

如果stream是在文本模式下打开,对于仅支持值offset为零(这与任何工作origin),并通过先前调用返回的值ftell与同一文件(仅与工作相关的物流originSEEK_SET)。

如果stream是面向广域的,则应用文本流和二进制流的限制(ftellSEEK_SET允许使用结果,SEEK_SET和SEEK_CUR允许使用零偏移量,但不允许SEEK_END)。

除了更改文件位置指示符之外,还可以fseek取消ungetc文件结束状态的效果并清除文件结束状态(如果适用)。

如果发生读取或写入错误,则会ferror设置stream()的错误指示符并且文件位置不受影响。

参数

-

文件流进行修改

抵消

-

将位置相对于原点移动的字符数

起源

-

添加了偏移量的位置。它可以具有以下值之一:SEEK_SET,SEEK_CUR,SEEK_END

返回值

0 一旦成功,否则非零值。

注意

在宽流中寻找非终点位置之后,对任何输出函数的下一次调用可能会使文件的其余部分不确定,例如通过输出不同长度的多字节序列。

对于文本流,唯一有效的值offset0(适用于任何origin)和先前调用返回的值ftell(仅适用于SEEK_SET)。

POSIX允许在现有的文件结尾之外寻找。如果在此查找后执行输出,则从间隙读取的数据将返回零字节。在文件系统支持的地方,这将创建一个稀疏文件

fflush如果有任何未写入的数据(但是移位状态是否恢复为实现定义),POSIX还要求fseek首先执行。

带有错误检查的fseek。

#include <stdio.h>#include <stdlib.h>
 int main(void){    /* Prepare an array of f-p values. */
    #define SIZE 5
    double A[SIZE] = {1.,2.,3.,4.,5.};    /* Write array to a file. */
    FILE * fp = fopen("test.bin", "wb");    fwrite(A,sizeof(double),SIZE,fp);    fclose (fp); 
    /* Read the f-p values into array B. */
    double B[SIZE];
    fp = fopen("test.bin","rb"); 
    /* Set the file position indicator in front of third f-p value. */    if (fseek(fp,sizeof(double)*2L,SEEK_SET) != 0)    {       if (ferror(fp))       {          perror("fseek()");          fprintf(stderr,"fseek() failed in file %s at line # %d\n", __FILE__,__LINE__-5);          exit(EXIT_FAILURE);       }    }
 
    int ret_code = fread(B,sizeof(double),1,fp);   /* read one f-p value  */    printf("%.1f\n", B[0]);                        /* print one f-p value */ 
    fclose(fp);    return EXIT_SUCCESS;}

输出:

3.0

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.21.9.2 fseek函数(p:336-337)

  • C99标准(ISO / IEC 9899:1999):

    • 7.19.9.2 fseek函数(p:302-303)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.9.9.2 fseek函数

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