c++11 标准模板（STL）本地化库 - std::isalnum(std::locale) 检查字符是否被本地环境分类为字母或数字

本地化库

本地环境设施包含字符分类和字符串校对、数值、货币及日期/时间格式化和分析，以及消息取得的国际化支持。本地环境设置控制流 I/O 、正则表达式库和 C++ 标准库的其他组件的行为。

检查字符是否被本地环境分类为字母或数字

std::isalnum(std::locale)

检查给定字符是否为给定 locale 的 std::ctype 平面分类为字母数字字符。

参数

返回值

若字符被分类为字母数字则返回 true ，否则返回 false 。

可能的实现

template< class charT >
bool isalnum( charT ch, const std::locale& loc ) {
    return std::use_facet<std::ctype<charT>>(loc).is(std::ctype_base::alnum, ch);
}

调用示例

#include <iostream>
#include <locale>

void try_with(wchar_t c, const char* locale)
{
    //检查给定字符是否为给定 locale 的 std::ctype 平面分类为字母数字字符。
    std::cout << "isalnum('"
              << c
              << "', locale(\""
              << locale
              << "\")) returned "
              << std::boolalpha
              << std::isalnum(c, std::locale(locale))
              << std::endl;
}

int main()
{
    //检查给定的字符在当前的 C 本地环境中是否是空白字符。
    //空格 (0x20, ' ')
    //换页(0x0c, '\f')
    //换行(0x0a, '\n')
    //回车(0x0d, '\r')
    //水平制表符(0x09, '\t')
    //垂直制表符(0x0b, '\v')

    std::cout << std::boolalpha;

    std::locale locale1;  // locale1 是经典 "C" 本地环境的副本
    std::cout << "locale1.name():   " << locale1.name() << std::endl;

    std::locale locale2("Chinese (Simplified)_China.936"); // locale2 为本地环境
    std::cout << "locale2.name():   " << locale2.name() << std::endl;

    const wchar_t isalnumC = L'\u042f'; // 西里尔大写字母 ya
    try_with(isalnumC, locale1.name().c_str());
    try_with(isalnumC, locale2.name().c_str());
    std::cout << std::endl;

    const wchar_t isalnumC2 = '1'; // ASCII '1'
    try_with(isalnumC2, locale1.name().c_str());
    try_with(isalnumC2, locale2.name().c_str());
    std::cout << std::endl;

    const wchar_t isalnumC3 = 1; // ASCII 1
    try_with(isalnumC3, locale1.name().c_str());
    try_with(isalnumC3, locale2.name().c_str());
    std::cout << std::endl;

    const wchar_t isalnumC4 = 'a'; // ASCII a
    try_with(isalnumC4, locale1.name().c_str());
    try_with(isalnumC4, locale2.name().c_str());
    std::cout << std::endl;

    const wchar_t isalnumC5 = ','; // ASCII ','
    try_with(isalnumC5, locale1.name().c_str());
    try_with(isalnumC5, locale2.name().c_str());
    std::cout << std::endl;

    const wchar_t isalnumC6 = ' '; // ASCII ' '
    try_with(isalnumC6, locale1.name().c_str());
    try_with(isalnumC6, locale2.name().c_str());
    std::cout << std::endl;

    return 0;
}

输出

locale1.name():   C
locale2.name():   Chinese (Simplified)_China.936
isalnum('1071', locale("C")) returned true
isalnum('1071', locale("Chinese (Simplified)_China.936")) returned true

isalnum('49', locale("C")) returned true
isalnum('49', locale("Chinese (Simplified)_China.936")) returned true

isalnum('1', locale("C")) returned false
isalnum('1', locale("Chinese (Simplified)_China.936")) returned false

isalnum('97', locale("C")) returned true
isalnum('97', locale("Chinese (Simplified)_China.936")) returned true

isalnum('44', locale("C")) returned false
isalnum('44', locale("Chinese (Simplified)_China.936")) returned false

isalnum('32', locale("C")) returned false
isalnum('32', locale("Chinese (Simplified)_China.936")) returned false