std_format.md

std::format is a feature introduced in C++20 that provides a type-safe and extensible way to format text. It's designed to be a safer, more robust replacement for older C-style formatting functions like printf and C++ stream-based formatting. The std::format function resides in the <format> header.

Basic Usage

The basic syntax of std::format is straightforward:

#include <format>
#include <iostream>

int main() {
    std::string message = std::format("Hello, {}!", "world");
    std::cout << message << std::endl;  // Output: Hello, world!
}

Format Specifiers

std::format uses format specifiers within the format string to indicate how to format the arguments. The format specifiers are enclosed in curly braces {}.

std::string formatted = std::format("The answer is {}.", 42);

Positional Arguments

You can specify the position of the arguments to be formatted:

std::string formatted = std::format("{1} before {0}", "world", "Hello");
// Output: "Hello before world"

Type-Specific Formatting

You can specify the type of formatting you want for each argument:

Integers: You can specify the base, padding, etc.

std::string hex_format = std::format("Hex: {:x}", 255);  
// Output: 
// "Hex: ff"

Floating-Point Numbers: You can specify the precision, scientific notation, etc.

std::string float_format = std::format("Float: {:.2f}", 3.14159);  
// Output: 
// "Float: 3.14"

Strings: You can specify the alignment and width.

std::string string_format = std::format("String: {:>10}", "right");  
// Output: 
// "String:      right"

Error Handling

One of the advantages of std::format is that it's type-safe. If you try to use a format specifier that's incompatible with the type of the argument, it will result in a compile-time error.

Performance

std::format is generally more efficient than using string streams for formatting, although it might not be as fast as printf in some cases. However, the type safety and extensibility often make it a better choice.