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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
characters

在头文件<string.h>中定义




(1)


void * memcpy(void * dest,const void * src,size_t count);

(直到C99)


void * memcpy(void * restrict dest,const void * restrict src,size_t count);

(自C99以来)


errno_t memcpy_s(void * restrict dest,rsize_t destsz,const void * restrict src,rsize_t count);

(2)

(自C11以来)

1)复制src指向的对象中的字符到dest指向的对象。 两个对象都被解释为无符号字符数组。

如果访问超出dest数组的末尾,则行为未定义。 如果对象重叠(这违反了限制合同)(自C99以来),行为未定义。 如果dest或src是空指针,则行为是未定义的。

2)与(1)相同,只是在运行时检测到以下错误并导致整个目标范围[dest,dest + destsz)被清零(如果dest和destsz都有效),并且调用当前 安装约束处理函数:

  • dest或者src是空指针

  • destszcount大于RSIZE_MAX

  • count大于destsz(会发生缓冲区溢出)

  • 源和目标对象重叠

如果由dest <count <= destsz指向的字符数组的大小,行为是未定义的; 换句话说,destsz的错误值不会暴露即将发生的缓冲区溢出。 作为所有边界检查的函数,只有当__STDC_LIB_EXT1__由实现定义并且用户在包含string.h之前将__STDC_WANT_LIB_EXT1__定义为整数常量1时,memcpy_s才能保证可用。

参数

dest

-

指向要复制到的对象的指针

destsz

-

在目标中修改的最大字节数(通常是目标对象的大小)

src

-

指向要从中复制的对象的指针

count

-

要复制的字节数

返回值

1)返回一份dest 副本

2)成功时返回零,错误时返回非零值。 同样出错的是,如果dest不是空指针且destsz有效,则将destsz零字节写入目标数组。

注意

memcpy 可用于设置由分配函数获得的对象的有效类型。

memcpy是内存到内存拷贝速度最快的库例程。 它通常比strcpy更高效,它必须扫描它拷贝或移除的数据,这必须采取预防措施来处理重叠输入。

几个C编译器将合适的内存复制循环转换为memcpy调用。

在严格别名禁止检查与两种不同类型的值相同的内存的情况下,memcpy可以用来转换这些值。

#define __STDC_WANT_LIB_EXT1__ 1#include <stdio.h>#include <stdint.h>#include <inttypes.h>#include <string.h>#include <stdlib.h>
 int main(void){    // simple usage
    char source[] = "once upon a midnight dreary...", dest[4];    memcpy(dest, source, sizeof dest);    for(size_t n = 0; n < sizeof dest; ++n)        putchar(dest[n]); 
    // setting effective type of allocated memory to be int
    int *p = malloc(3*sizeof(int));   // allocated memory has no effective type
    int arr[3] = {1,2,3};    memcpy(p,arr,3*sizeof(int));      // allocated memory now has an effective type 
    // reinterpreting data
    double d = 0.1;//    int64_t n = *(int64_t*)(&d); // strict aliasing violation
    int64_t n;    memcpy(&n, &d, sizeof d); // OK    printf("\n%a is %" PRIx64 " as an int64_t\n", d, n);
 #ifdef __STDC_LIB_EXT1__    set_constraint_handler_s(ignore_handler_s);
    char src[] = "aaaaaaaaaa";
    char dst[] = "xyxyxyxyxy";
    int r = memcpy_s(dst,sizeof dst,src,5);    printf("dst = \"%s\", r = %d\n", dst,r);
    r = memcpy_s(dst,5,src,10);            //  count is greater than destsz      printf("dst = \"");    for(size_t ndx=0; ndx<sizeof dst; ++ndx) {
        char c = dst[ndx];
        c ? printf("%c", c) : printf("\\0");    }    printf("\", r = %d\n", r);#endif}

可能的输出:

once0x1.999999999999ap-4 is 3fb999999999999a as an int64_t
dst = "aaaaayxyxy", r = 0dst = "\0\0\0\0\0yxyxy", r = 22

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.24.2.1 memcpy函数(p:362)

    • K.3.7.1.1 memcpy_s函数(p:614)

  • C99标准(ISO / IEC 9899:1999):

    • 7.21.2.1 memcpy函数(p:325)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.11.2.1 memcpy函数

扩展内容

memmovememmove_s(C11)

移动一个缓冲区到另一个(功能)

wmemcpywmemcpy_s(C95)(C11)

在两个非重叠数组之间复制一定数量的宽字符(函数)

| 用于memcpy的C ++文档 |

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在头文件<wctype.h>中定义



int iswdigit(wint_t ch);


(自C95以来)

检查给定的宽字符是否对应(如果缩小)十个十进制数字字符0123456789中的一个。

参数

CH

-

宽字符

返回值

如果宽字符是数字字符,则为非零值,否则为零。

注意

iswdigitiswxdigit是唯一不受当前安装的C语言环境影响的标准宽字符分类函数。

一些语言环境提供了检测非ASCII数字的附加字符类。

#include <stdio.h>#include <wctype.h>#include <wchar.h>#include <locale.h> void test(wchar_t a3, wchar_t u3, wchar_t j3){    printf("        '%lc' '%lc' '%lc'\n", a3, u3, j3);    printf("iswdigit %d    %d   %d\n",           !!iswdigit(a3), !!iswdigit(u3), !!iswdigit(j3));    printf("jdigit:  %d    %d   %d\n", !!iswctype(a3, wctype("jdigit")),          !!iswctype(u3, wctype("jdigit")),          !!iswctype(j3, wctype("jdigit")));}
 int main(void){
    wchar_t a3 = L'3';  // the ASCII digit 3
    wchar_t u3 = L'三'; // the CJK numeral 3
    wchar_t j3 = L'3'; // the fullwidth digit 3 
    setlocale(LC_ALL, "en_US.utf8");    puts("In American locale:");    test(a3, u3, j3); 
    setlocale(LC_ALL, "ja_JP.utf8");    puts("\nIn Japanese locale:");    test(a3, u3, j3);}

输出:

In American locale:        '3' '三' '3'iswdigit 1    0   0jdigit:  0    0   0
 In Japanese locale:        '3' '三' '3'iswdigit 1    0   0jdigit:  0    0   1

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.30.2.1.5 iswdigit函数(p:449)

  • C99标准(ISO / IEC 9899:1999):

    • 7.25.2.1.5 iswdigit函数(p:395)

扩展内容

isdigit

检查一个字符是否是一个数字(功能)

| 用于iswdigit的C ++文档 |

ASCII 值  (十六进制)

字符

iscntrl  iswcntrl.

isprint  iswprint.

isspace  iswspace.

isblank  iswblank.

isgraph  iswgraph.

ispunct  iswpunct.

isalnum  iswalnum.

isalpha  iswalpha.

isupper  iswupper.

islower  iswlower.

isdigit  iswdigit.

isxdigit  iswxdigit.


0 - 8

0x00-0x08

控制码 (NUL, etc.)

≠0

0

0

0

0

0

0

0

0

0

0

0

9

0x09

tab (\t)

≠0

0

≠0

≠0

0

0

0

0

0

0

0

0

10 - 13

0x0A-0x0D

空格 (\n,\v,\f,\r)

≠0

0

≠0

0

0

0

0

0

0

0

0

0

14 - 31

0x0E-0x1F

控制码

≠0

0

0

0

0

0

0

0

0

0

0

0

32

0x20

space

0

≠0

≠0

≠0

0

0

0

0

0

0

0

0

33 - 47

0x21-0x2F

!"#$%&'()*+,-./

0

≠0

0

0

≠0

≠0

0

0

0

0

0

0

48 - 57

0x30-0x39

0123456789

0

≠0

0

0

≠0

0

≠0

0

0

0

≠0

≠0

58 - 64

0x3a-0x40

:;<=>?@

0

≠0

0

0

≠0

≠0

0

0

0

0

0

0

65 - 70

0x41-0x46

ABCDEF

0

≠0

0

0

≠0

0

≠0

≠0

≠0

0

0

≠0

71 - 90

0x47-0x5A

GHIJKLMNOPQRSTUVWXYZ

0

≠0

0

0

≠0

0

≠0

≠0

≠0

0

0

0

91 - 96

0x5B-0x60

[]^_` | 0 | ≠0 | 0 | 0 | ≠0 | ≠0 | 0 | 0 | 0 | 0 | 0 | 0 |













97 -102

0x61-0x66

abcdef

0

≠0

0

0

≠0

0

≠0

≠0

0

≠0

0

≠0

103-122

0x67-0x7A

ghijklmnopqrstuvwxyz

0

≠0

0

0

≠0

0

≠0

≠0

0

≠0

0

0

123-126

0x7B-0x7E

{|}~

0

≠0

0

0

≠0

≠0

0

0

0

0

0

0

127

0x7F

退格 (DEL)

≠0

0

0

0

0

0

0

0

0

0

0

0

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