How can I format currency with commas in C?
#include <stdio.h>
#include <locale.h>

int main(void)
{
    setlocale(LC_NUMERIC, "");
    printf("$%'.2Lfn", 123456789.00L);
    printf("$%'.2Lfn", 1234.56L);
    printf("$%'.2Lfn", 123.45L);
    return 0;
}

> make example
clang -Wall -Wextra -Werror    example.c   -o example
> ./example
$123,456,789.00
$1,234.56
$123.45