C++ 字符格式化输出

一、简介

这里使用std标准库简单实现一个字符格式化输出，方便后续的使用，它有点类似Qt中的QString操作。

二、实现代码

FMTString.hpp

#pragma once#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <optional>
#include <random>
#include <type_traits>
#include <sstream>namespace FMT 
{void formatStream(std::stringstream& stream, char const* text) {stream << text;return;}/// <summary>/// 在编译时检测某个类型T是否支持通过 operator<< 输出到流（如std::stringstream）/// </summary>/// <typeparam name="T"></typeparam>template <class T>class IsStreamable {private:template <class TT>static auto test(int)-> decltype(std::declval<std::stringstream&>() << std::declval<TT>(),std::true_type());template <class>static auto test(...)->std::false_type;public:static bool const value = decltype(test<T>(0))::value;};/// <summary>/// 将任意类型的参数通过流操作符 << 转换为字符串流（std::stringstream）的内容/// </summary>/// <typeparam name="T"></typeparam>template <class T>class ArgToStream {public:static void impl(std::stringstream& stream, T&& arg) {stream << std::forward<T>(arg);}};/// <summary>/// 将格式字符串 text 中的 {} 占位符依次替换为传入的参数 arg, args...，并将结果写入 std::stringstream 流中/// </summary>/// <typeparam name="T"></typeparam>/// <typeparam name="...Args"></typeparam>/// <param name="stream"></param>/// <param name="text"></param>/// <param name="arg"></param>/// <param name="...args"></param>template <class T, typename... Args>void formatStream(std::stringstream& stream, char const* text, T&& arg,Args&&... args) {static_assert(IsStreamable<T>::value,"One of the args has no ostream overload!");for (; *text != '\0'; ++text) {if (*text == '{' && *(text + 1) == '}') {ArgToStream<T&&>::impl(stream, std::forward<T>(arg));formatStream(stream, text + 2, std::forward<Args>(args)...);return;}stream << *text;}stream << "\nFormat-Warning: There are " << sizeof...(Args) + 1<< " args unused.";return;}template <class... Args>std::string formatString(char const* text, Args&&... args) {std::stringstream stream;formatStream(stream, text, std::forward<Args>(args)...);return stream.str();}
}

main.cpp

// 标准文件
#include <iostream>
#include <string>#include "FMTString.hpp"int main(int, char** argv)
{std::string msg = FMT::formatString("Hello, {}! You have {} new messages.", "Alice", 5);std::cout << "Output:" << msg << std::endl;system("pause");return 0;
}

三、实现效果