do_length
STD：：codecvt：：长度，做[医]长度
| Defined in header | | |
|---|---|---|
| public: int length( StateT& state, const ExternT* from, const ExternT* from_end, std::size_t max ) const; | (1) | |
| protected: virtual int do_length( StateT& state, const ExternT* from, const ExternT* from_end, std::size_t max ) const; | (2) | |
1%29公共成员函数，调用成员函数。do_length最派生的类。
2%29次尝试转换externT定义的字符数组中的字符。[from, from_end)，给定初始转换状态state，最多maxinternT字符，并返回externT这种转换将消耗的字符。修改state仿佛通过执行do_in(state, from, from_end, from, to, to+max, to)对某个想象中的人来说[to, to+max)输出缓冲器
返回值
的数目externT如果转换为do_in()直到所有from_end-from字符被消耗或maxinternT生成字符，或发生转换错误。
非转换专业化std::codecvt<char, char,std::mbstate_t>回报std::min(max, from_end-from)...
例
二次
#include <locale>
#include <string>
#include <iostream>
int main()
{
// narrow multibyte encoding
std::string s = "z\u00df\u6c34\U0001d10b"; // or u8"zß水?"
// or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";
std::mbstate_t mb = std::mbstate_t(
std::cout << "Only the first " <<
std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
std::locale("en_US.utf8")
).length(mb, &s[0], &s[s.size()], 2)
<< " bytes out of " << s.size() << " would be consumed "
" to produce the first 2 characters\n";
}
二次
产出：
二次
Only the first 3 bytes out of 10 would be consumed to produce the first 2 characters
二次
另见
| do_in virtual | converts a string from externT to internT, such as when reading from file (virtual protected member function) |
|---|
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