How to Format Numbers with Commas in C Using std::locale?

Formatting Numbers with Commas in C

In C , the std::locale class provides a locale-dependent way to format numbers with commas.

std::locale with std::stringstream

To format a number as a string with commas, you can use std::locale with std::stringstream as follows:

<code class="cpp">#include <iomanip>
#include <locale>

template<class T>
std::string FormatWithCommas(const T& value) {
  std::stringstream ss;
  ss.imbue(std::locale(""));  // Use the system's locale
  ss << std::fixed << value;
  return ss.str();
}</code>

Example Usage:

<code class="cpp">std::string result1 = FormatWithCommas(7800);
std::string result2 = FormatWithCommas(5100100);
std::string result3 = FormatWithCommas(201234567890);

// result1 = "7,800"
// result2 = "5,100,100"
// result3 = "201,234,567,890"</code>

Handling Doubles

To format a double as a string with commas, you can use the same approach as above, but the code will need to handle the decimal point:

<code class="cpp">template<class T>
std::string FormatWithCommas(const T& value) {
  std::stringstream ss;
  ss.imbue(std::locale(""));
  ss << std::fixed << std::setprecision(2) << value;
  return ss.str();
}</code>

Disclaimer:

Note that the portability of the above solutions might be an issue, as the locale used when "" is passed may vary depending on the system.

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