std::codecvt<InternT,ExternT,State>::max_length, do_max_length
来自cppreference.com
| 定义于头文件 <locale>
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||
| (1) | ||
| public: int max_length() const throw(); |
(C++11 前) | |
| public: int max_length() const noexcept; |
(C++11 起) | |
| (2) | ||
| protected: virtual int do_max_length() const throw(); |
(C++11 前) | |
| protected: virtual int do_max_length() const noexcept; |
(C++11 起) | |
1) 公开成员函数，调用最终派生类的成员函数
do_max_length 。2) 返回对于任何合法范围
[from, from_end) 和任何 state 合法 ， do_length(state, from, from_end, 1) 所能返回的最大值。返回值
若以 in() 转换生成一个 InternT 字符，能消耗的最大 ExternT 字符数。
不转换特化 std::codecvt<char, char, std::mbstate_t> 返回 1 。
注意
若编码依赖状态（ encoding() == -1 ），则可能消耗多于 max_length() 个外部字符生成一个内部字符。
示例
运行此代码
#include <locale> #include <iostream> #include <codecvt> int main() { std::cout << "In codecvt_utf8, the longest multibyte character is " << std::codecvt_utf8<wchar_t>().max_length() << " bytes long\n"; std::cout << "In header-consuming codecvt_utf8, the longest multibyte character is " << std::codecvt_utf8<wchar_t, 0x10ffff, std::consume_header>().max_length() << " bytes long\n"; std::cout << "In this system's en_US.utf8, the longest multibyte character is " << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>( std::locale("en_US.utf8") ).max_length() << " bytes long\n"; std::cout << "In this system's zh_CN.gb18030, the longest multibyte character is " << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>( std::locale("zh_CN.gb18030") ).max_length() << " bytes long\n"; }
输出：
In codecvt_utf8, the longest multibyte character is 4 bytes long In header-consuming codecvt_utf8, the longest multibyte character is 7 bytes long In this system's en_US.utf8, the longest multibyte character is 6 bytes long In this system's zh_CN.gb18030, the longest multibyte character is 4 bytes long
参阅
| MB_CUR_MAX |
当前 C 本地环境中多字节字符的最大字节数 (宏变量) |
| [虚] |
返回产生一个 internT 字符所需的 externT 字符数，若此值为常数 (虚受保护成员函数) |