C++20的std::format库怎么用_C++字符串格式化新特性详解

#include <format>
#include <iostream>

int main() {
    std::string name = "Alice";
    int age = 30;
    
    std::string result = std::format("Hello, {}! You are {} years old.", name, age);
    std::cout << result << '\n';
    // 输出: Hello, Alice! You are 30 years old.
}

std::string s = std::format("{1} is {0} years old.", age, name);
// 输出: Alice is 30 years old.

std::cout << std::format("|{:<8}|{:>8}|{:^8}|\n", "left", "right", "center");
// 输出: |left    |   right| center |

std::cout << std::format("{:05}", 42);     // 输出: 00042
std::cout << std::format("{:.3f}", 3.14159); // 输出: 3.142

std::format("{}", true)     // "true"
std::format("{:d}", true)   // "1"

struct Point {
    double x, y;
};

template<>
struct std::formatter<Point> {
    constexpr auto parse(auto& ctx) { return ctx.begin(); }

    auto format(const Point& p, auto& ctx) const {
        return std::format_to(ctx.out(), "({:.1f}, {:.1f})", p.x, p.y);
    }
};

// 使用
std::format("Position: {}", Point{1.23, 4.56}); 
// 输出: Position: (1.2, 4.6)

auto size = std::formatted_size("Value: {}", 42); // 返回所需大小

char buffer[64];
std::format_to(buffer, "Hello, {}", "World");