How Can I Format Output Using the C Output Operator (`

Formatting Output Using the Output Operator (<<)

You seek a method to format output using the output operator (<<) in C . While you could utilize printf, you favor the use of the output operator.

Solution

The following code effectively formats output using the output operator:

#include <iostream>
#include <iomanip>

using namespace std;

int main() {
  int zipCode = 12345;
  cout << setw(5) << setfill('0') << zipCode << endl;

  return 0;
}</h2>
<p>This code utilizes IO manipulators to control padding:</p>
<ul>
<li>setw(width) sets the field width to five.</li>
<li>setfill(fillchar) sets the fill character to '0'.</li>
</ul>
<p>This results in the ZIP code being formatted with leading zeros: 012345.</p>
<h2>Alternative Approaches</h2>
<p>If you prefer a more concise approach, you can use the fmt library:</p>
<pre class="brush:php;toolbar:false">cout << fmt::format("{:05d}", zipCode);

In C 20 and later, the std::format functionality is available:

cout << std::format("{:05d}", zipCode);

Considerations

Note that these IO manipulators affect the global state of cout. Subsequent usages of cout will be impacted unless the manipulations are explicitly undone.

For negative numbers, use std::internal to place the fill character between the sign and the magnitude:

cout << internal << setw(5) << setfill('0') << zipCode << endl;

You can safely assume that all ZIP codes are non-negative, but this is an assumption nonetheless.

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