How can I pad an int with leading zeros when using cout

Question

I want cout to output an int with leading zeros, so the value 1 would be printed as 001 and the value 25 printed as 025. How can I do this?

user_471164 · Answer

In C++20 you'll be able to do:

std::cout << std::format("{:03}", 25); // prints 025

In the meantime you can use the {fmt} library, std::format is based on.

Disclaimer: I'm the author of {fmt} and C++20 std::format.

How can I pad an int with leading zeros when using cout << operator?