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generationrandRAND_MAXremainderremainderfremainderlremquoremquofremquolrintrintfrintlroundroundfroundlscalblnscalblnfscalblnlscalbnscalbnfscalbnlsignbitsinsinfsinhsinhfsinhlsinlsqrtsqrtfsqrtlsrandtantanftanhtanhftanhltanltgammatgammaftgammaltrunctruncftrunclType-generic math_Complex_I_Imaginary_IProgram supportabortatexitat_quick_exitexitEXIT_FAILUREEXIT_SUCCESSgetenvgetenv_sjmp_buflongjmpProgram support utilitiesquick_exitraisesetjmpSIGABRTSIGFPESIGILLSIGINTsignalSIGSEGVSIGTERMsig_atomic_tSIG_DFLSIG_ERRSIG_IGNsystem_ExitStringsatofatoiatolatollbtowcc16rtombc32rtombchar16_tchar32_tisalnumisalphaisblankiscntrlisdigitisgraphislowerisprintispunctisspaceisupperiswalnumiswalphaiswblankiswcntrliswctypeiswdigitiswgraphiswloweriswprintiswpunctiswspaceiswupperiswxdigitisxdigitmblenmbrlenmbrtoc16mbrtoc32mbrtowcmbsinitmbsrtowcsmbsrtowcs_smbstate_tmbstowcsmbstowcs_smbtowcmemchrmemcmpmemcpymemcpy_smemmovememmove_smemsetmemset_sNull-terminated byte stringsNull-terminated multibyte 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文字

在头文件<string.h>中定义




(1)


char * strncat(char * dest,const char * src,size_t count);

(直到C99)


char * strncat(char * restrict dest,const char * restrict src,size_t count);

(自C99以来)


errno_t strncat_s(char * restrict dest,rsize_t destsz,const char * restrict src,rsize_t count);

(2)

(自C11以来)

1)追加由src指向的字符数组中的大多数计数字符,如果找到空字符,则停止到由dest指向的以null结尾的字节字符串的末尾。 字符src [0]替换dest结尾处的空终止符。 终止空字符总是附加在最后(因此函数可以写入的最大字节数为count + 1)。

如果目标数组没有足够的空间用于dest和src的第一个计数字符的内容以及终止的空字符,则行为未定义。 如果源和目标对象重叠,则行为未定义。 如果dest不是指向以空字符结尾的字节字符串的指针,或者src不是指向字符数组的指针,则行为未定义.

2)与(1)相同,只是此函数可能会打断目标数组的其余部分(从写入到destsz的最后一个字节开始),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:

  • src或者dest是空指针

  • destsz或者count是零或大于RSIZE_MAX

  • 在第一个destsz字节中没有空字符dest

  • 则会发生截断:count或者src较小者的长度超过了destdestsz的空终止符之间的可用空间。

  • 源和目标字符串之间会发生重叠

如果由dest <strnlen(dest,destsz)+ strnlen(src,count)+1 <destsz;指向的字符数组的大小,则行为是不确定的。 换句话说,destsz的错误值不会暴露即将发生的缓冲区溢出。 如果字符数组的大小由src <strnlen(src,count)<destsz; 换句话说,count的错误值不会暴露即将发生的缓冲区溢出。 作为所有边界检查函数,只有当__STDC_LIB_EXT1__由实现定义并且在包含string.h之前用户将__STDC_WANT_LIB_EXT1__定义为整数常量1时,strncat_s才能保证可用。

参数

dest

-

指向要附加到的以空字符结尾的字节字符串

SRC

-

指向要复制的字符数组的指针

count

-

最大数量的字符复制

destsz

-

目标缓冲区的大小

返回值

1)返回 dest 副本

2)在成功时返回零,错误时返回非零值。 另外,如果发生错误,则将零写入dest [0](除非dest是空指针或destsz为零或大于RMAX_SIZE)。

注意

尽管适合目标缓冲区的截断存在安全风险,并且因此违反了strncat_s的运行时间约束,但可以通过指定count等于目标数组的大小减1来获得截断行为:它将复制第一个计数字节和 像往常一样添加空终止符:strncat_s(dst,sizeof dst,src,(sizeof dst)-strnlen_s(dst,sizeof dst)-1);

#define __STDC_WANT_LIB_EXT1__ 1#include <string.h> #include <stdio.h>#include <stdlib.h>
 int main(void) {
    char str[50] = "Hello ";
    char str2[50] = "World!";    strcat(str, str2);    strncat(str, " Goodbye World!", 3);    puts(str);
 #ifdef __STDC_LIB_EXT1__    set_constraint_handler_s(ignore_handler_s);
    char s1[100] = "good";
    char s5[1000] = "bye";
    int r1 = strncat_s(s1, 100, s5, 1000); // r1 is 0, s1 holds "goodbye\0"    printf("s1 = %s, r1 = %d\n", s1, r1);
    char s2[6] = "hello";
    int r2 = strncat_s(s2, 6, "", 1); // r2 is 0, s2 holds "hello\0"    printf("s2 = %s, r2 = %d\n", s2, r2);
    char s3[6] = "hello";
    int r3 = strncat_s(s3, 6, "X", 2); // r3 is non-zero, s3 holds "\0"    printf("s3 = %s, r3 = %d\n", s3, r3);    // the strncat_s truncation idiom:
    char s4[7] = "abc";
    int r4 = strncat_s(s4, 7, "defghijklmn", 3); // r is 0, s4 holds "abcdef\0"    printf("s4 = %s, r4 = %d\n", s4, r4);#endif}

可能的输出:

Hello World! Go
s1 = goodbye, r1 = 0s2 = hello, r2 = 0s3 = , r3 = 22s4 = abcdef, r4 = 0

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.24.3.2 strncat函数(p:364-365)

    • K.3.7.2.2 strncat_s函数(p:618-620)

  • C99标准(ISO / IEC 9899:1999):

    • 7.21.3.2 strncat函数(p:327-328)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.11.3.2 strncat函数

扩展内容

strcatstrcat_s(C11)

连接两个字符串(函数)

strcpystrcpy_s(C11)

将一个字符串复制到另一个(函数)

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

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9

0x09

tab (\t)

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10 - 13

0x0A-0x0D

空格 (\n,\v,\f,\r)

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0

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14 - 31

0x0E-0x1F

控制码

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32

0x20

space

0

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33 - 47

0x21-0x2F

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

0

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48 - 57

0x30-0x39

0123456789

0

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58 - 64

0x3a-0x40

:;<=>?@

0

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65 - 70

0x41-0x46

ABCDEF

0

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71 - 90

0x47-0x5A

GHIJKLMNOPQRSTUVWXYZ

0

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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

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103-122

0x67-0x7A

ghijklmnopqrstuvwxyz

0

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123-126

0x7B-0x7E

{|}~

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127

0x7F

退格 (DEL)

≠0

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