std::format in C++

C++20's answer to printf: type-checked templates with alignment, precision, and bases.

#include <format>
#include <iostream>
#include <string>

int main() {
    std::string label = "latency";
    double ms = 4.276;
    std::cout << std::format("{:<10} {:>8.2f} ms\n", label, ms);
    std::cout << std::format("{0} of {1} ({2:.1f}%)\n",
                             45, 60, 100.0 * 45 / 60);
    std::cout << std::format("hex {0:#06x}  binary {0:#b}\n", 42);
}

How it works

1. {:<10} left-aligns the label; {:>8.2f} right-aligns the number to two decimals.
2. Arguments can be addressed by index — {0} and {1} reuse them in any order.
3. {0:#06x} and {0:#b} print the same 42 in zero-padded hex and in binary.

Keywords and builtins used here

• double
• int
• main

The run, in numbers

Lines

12

Characters to type

323

Tokens

97

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 83 seconds.

Type this snippet

Step 3 of 3 in Strings & streams, step 21 of 27 in Language basics.

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