do_narrow

Defined in header <locale>
public: char narrow( CharT c, char dflt ) const;	(1)
public: const CharT* narrow( const CharT* beg, const CharT* end, char dflt, char* dst ) const;	(2)
protected: virtual char do_narrow( CharT c, char dflt ) const;	(3)
protected: virtual const CharT* do_narrow( const CharT* beg, const CharT* end, char dflt, char* dst ) const;	(4)

1，2%29公共成员函数，调用受保护的虚拟成员函数do_narrow最派生的类。

3%29转换%28可能宽的%29字符c例如，如果字符可以用单个字节%28表示，那么UTF-8编码中的ASCII字符是单字节%29。回报dflt如果不存在这种转换。

4%29对字符数组中的每个字符[beg, end)，写入缩小字符%28或dflt每当将%29缩小到指向的字符数组中的连续位置时，dst...

缩窄总是成功的，并且通过调用widen()%29用于编写C++程序%29所需的基本源字符集%28 latin字母、数字和标点符号的所有字符。

如果收缩成功，则保留已知的所有字符分类类别。is()...

缩小任何数字字符可以保证如果从字符文字中减去结果'0'，此差异等于原始字符的数字值。

参数

c	-	character to convert
dflt	-	default value to produce if the conversion fails
beg	-	pointer to the first character in an array of characters to convert
end	-	one past the end pointer for the array of characters to convert
dst	-	pointer to the first element of the array of char to fill

返回值

1，3%29缩小字符或dflt如果收缩失败

2，4%29end

例

二次

#include <locale>
#include <iostream>
 
void try_narrow(const std::ctype<wchar_t>& f, wchar_t c)
{
    char n = f.narrow(c, 0);
    if (n) {
        std::wcout << '\'' << c << "' narrowed to " << +(unsigned char)n << '\n';
    } else {
        std::wcout << '\'' << c << "' could not be narrowed\n";
    }
}
 
int main()
{
    std::locale::global(std::locale("en_US.utf8"));
    std::wcout.imbue(std::locale());
    std::wcout << std::hex << std::showbase << "In US English UTF-8 locale:\n";
    auto& f = std::use_facet<std::ctype<wchar_t>>(std::locale());
    try_narrow(f, L'A');
    try_narrow(f, L'Ａ');
    try_narrow(f, L'ě');
 
    std::locale::global(std::locale("cs_CZ.iso88592"));
    auto& f2 = std::use_facet<std::ctype<wchar_t>>(std::locale());
    std::wcout << "In Czech ISO-8859-2 locale:\n";
    try_narrow(f2, L'A');
    try_narrow(f2, L'Ａ');
    try_narrow(f2, L'ě');
}

二次

产出：

二次

In US English UTF-8 locale:
'A' narrowed to 0x41
'Ａ' could not be narrowed
'ě' could not be narrowed
In Czech ISO-8859-2 locale:
'A' narrowed to 0x41
'Ａ' could not be narrowed
'ě' narrowed to 0xec

二次

另见

widen	invokes do_widen (public member function)
narrow	narrows characters (public member function of std::basic_ios)
wctob	narrows a wide character to a single-byte narrow character, if possible (function)

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最后更新于：2017-12-18