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

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?

Answer 1

With the following,

#include <iomanip>
#include <iostream>

int main()
{
    std::cout << std::setfill('0') << std::setw(5) << 25;
}

the output will be

00025

setfill is set to the space character (' ') by default. setw sets the width of the field to be printed, and that's it.

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If you are interested in knowing how the to format output streams in general, I wrote an answer for another question, hope it is useful: Formatting C++ Console Output.