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文字

在头文件<uchar.h>中定义



size_t c16rtomb(char * s,char16_t c16,mbstate_t * ps);


(自C11以来)

将单个代码点从其可变长度的16位宽字符表示(通常为UTF-16)转换为其窄多字节字符表示形式。

如果s不是空指针并且c16是代码点的有效可变长度编码中的最后16位代码单元,则该函数确定存储该代码点的多字节字符表示所需的字节数(包括任何 移位序列),并将多字节字符表示存储在第一个元素由s指向的字符数组中。 该函数最多可以写入MB_CUR_MAX个字节。

如果s是空指针,那么对于某些内部缓冲区buf,调用等同于c16rtomb(buf,u'\ 0',ps)。

如果c16是空宽字符u'\ 0',则存储空字节,之前是恢复初始转换状态所需的任何转换序列,并且转换状态参数* ps被更新以表示初始转换状态。

如果c16不是宽字符的16位表示形式的最终代码单元,则它不会写入由s指向的数组,只会更新* ps。

如果定义了宏__STDC_UTF_16__,则该函数使用的16位编码为UTF-16; 否则,它是实现定义的。 在任何情况下,此函数使用的多字节字符编码均由当前活动的C语言环境指定。

参数

s

-

指向多字节字符将被存储在其中的窄字符数组的指针

C16

-

要转换的16位宽字符

PS

-

指向解释多字节字符串时使用的转换状态对象的指针

返回值

成功时,返回写入字符数组的第一个元素由s指向的字节数(包括任何移位序列)。 这个值可能是?0 ?,例如 当处理多char16_t单元序列中的前导char16_t单元时(发生在处理UTF-16的代理对中的前导代理时)。

失败时(如果c16不是有效的16位代码单元)则返回-1,将EILSEQ存储在errno中,并使* ps处于未指定状态。

注意

在发布的C11中,与将可变宽度多字节(如UTF-8)转换为可变宽度16位(如UTF-16)编码的mbrtoc16不同,此函数只能转换单个单元的16位编码, 这意味着它不能将UTF-16转换为UTF-8,尽管这是该功能的最初意图。 C11之后的缺陷报告DR488纠正了这一问题。

注意:此示例假定应用了缺陷报告488的修复。

#include <stdio.h>#include <locale.h>#include <uchar.h>#include <stdlib.h>
 mbstate_t state;int main(void){    setlocale(LC_ALL, "en_US.utf8");
    char16_t in[] = u"zß水?"; // or "z\u00df\u6c34\U0001F34C"
    size_t in_sz = sizeof in / sizeof *in; 
    printf("Processing %zu UTF-16 code units: [ ", in_sz);    for(size_t n = 0; n < in_sz; ++n) printf("%#x ", in[n]);    puts("]");
 
    char out[MB_CUR_MAX * in_sz];
    char *p = out;    for(size_t n = 0; n < in_sz; ++n) {
        int rc = c16rtomb(p, in[n], &state); 
        if(rc == -1) break;
        p += rc;    }
 
    size_t out_sz = p - out;    printf("into %zu UTF-8 code units: [ ", out_sz);    for(size_t x = 0; x < out_sz; ++x) printf("%#x ", +(unsigned char)out[x]);    puts("]");}

输出:

Processing 6 UTF-16 code units: [ 0x7a 0xdf 0x6c34 0xd83c 0xdf4c 0 ]into 11 UTF-8 code units: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c 0 ]

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.28.1.2 c16rtomb功能(p:399-400)

扩展内容

mbrtoc16(C11)

从一个窄多字节字符串(函数)生成下一个16位宽字符

| c16rtomb的C ++文档 |

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