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文字

在头文件<string.h>中定义



size_t strlen(const char * str);

(1)


size_t strnlen_s(const char * str,size_t strsz);

(2)

(自C11以来)

1)返回给定的以空字符结尾的字节字符串的长度,即字符数组中第一个元素由str指向并且不包含第一个空字符的字符数。

如果str不是指向以空字符结尾的字节字符串的指针,则行为是未定义的。

2)与(1)相同,只是如果str是空指针,则函数返回零,如果在str的第一个strsz字节中未找到空字符,则返回strsz。

如果两个str都指向缺少空字符和该字符数组大小的字符数组,则行为是未定义的<strsz; 换句话说,strsz的错误值不会暴露即将发生的缓冲区溢出。 与所有边界检查函数一样,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,strnlen_s才能保证可用。

参数

str

-

指向要检查的以空字符结尾的字节字符串

strsz

-

最大数量的字符进行检查

返回值

1)以空字符结尾的字节串str的长度。

2)成功时以空字符结尾的字节串str的长度,如果str是空指针则返回零,如果未找到空字符,则返回strsz。

注意

strnlen_swcsnlen_s是不调用运行时约束处理程序的唯一边界检查函数。它们是纯粹的实用函数,用于为非空终止的字符串提供有限的支持。

#define __STDC_WANT_LIB_EXT1__ 1#include <string.h>#include <stdio.h>
 int main(void){    const char str[] = "How many characters does this string contain?"; 
    printf("without null character: %zu\n", strlen(str));    printf("with null character:    %zu\n", sizeof str);
 #ifdef __STDC_LIB_EXT1__    printf("without null character: %zu\n", strnlen_s(str, sizeof str));#endif}

输出:

without null character: 45with null character:    46without null character: 45

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.24.6.3 strlen函数(p:372)

    • K.3.7.4.4 strnlen_s函数(p:623)

  • C99标准(ISO / IEC 9899:1999):

    • 7.21.6.3 strlen函数(p:334)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.11.6.3 strlen函数

扩展内容

wcslenwcsnlen_s(C95)(C11)

返回一个宽字符串的长度(函数)

mblen

返回下一个多字节字符(函数)中的字节数

| strlen的C ++文档 |

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.


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