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:

#include 
#include 

template
std::string FormatWithCommas(const T& value) {
  std::stringstream ss;
  ss.imbue(std::locale(""));  // Use the system's locale
  ss 
Example Usage:
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"
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:
template
std::string FormatWithCommas(const T& value) {
  std::stringstream ss;
  ss.imbue(std::locale(""));
  ss 
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.