std::mbrlen

STD：mbrlen

Defined in header
std::size_t mbrlen( const char* s, std::size_t n, std::mbstate_t* ps

确定其第一个字节指向的多字节字符的剩余部分的大小(以字节为单位)。s，给定当前的转换状态。ps...

此函数等效于调用。std::mbrtowc(nullptr, s, n, ps?ps:&internal)对于某个隐藏的对象internal类型std::mbstate_t，除了这句话ps只计算一次。

参数

s	-	pointer to an element of a multibyte character string
n	-	limit on the number of bytes in s that can be examined
ps	-	pointer to the variable holding the conversion state

返回值

0如果下一个n或者更少的字节完成空字符。

之间的字节数%281和n%29完成有效的多字节字符。

(size_t)-1如果出现编码错误。

(size_t)-2如果下一个n字节是可能有效的多字节字符的一部分，在检查完所有字符后，该字符仍然是不完整的。n字节。

例

二次

#include <clocale>
#include <string>
#include <iostream>
#include <cwchar>
 
int main()
{
    // allow mbrlen() to work with UTF-8 multibyte encoding
    std::setlocale(LC_ALL, "en_US.utf8"
    // UTF-8 narrow multibyte encoding
    std::string str = u8"水"; // or u8"\u6c34" or "\xe6\xb0\xb4"
    std::mbstate_t mb = std::mbstate_t(
    int len1 = std::mbrlen(&str[0], 1, &mb
    if(len1 == -2) {
        std::cout << "The first 1 byte of " << str
                  << " is an incomplete multibyte char (mbrlen returns -2)\n";
    }
    int len2 = std::mbrlen(&str[1], str.size()-1, &mb
    std::cout << "The remaining " << str.size()-1 << " bytes of " << str
              << " hold " << len2 << " bytes of the multibyte character\n";
    std::cout << "Attempting to call mbrlen() in the middle of " << str
              << " while in initial shift state returns "
              << (int)mbrlen(&str[1], str.size(), &mb) << '\n';
 
}

二次

产出：

二次

The first 1 byte of 水 is an incomplete multibyte char (mbrlen returns -2)
The remaining 2 bytes of 水 hold 2 bytes of the multibyte character
Attempting to call mbrlen() in the middle of 水 while in initial shift state returns -1

二次

另见

mbrtowc	converts the next multibyte character to wide character, given state (function)
mblen	returns the number of bytes in the next multibyte character (function)
do_length virtual	calculates the length of the externT string that would be consumed by conversion into given internT buffer (virtual protected member function of std::codecvt)

c为mbrlen编写的文件

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