问题：

I want to write a method that will take an integer and return a std::string of that integer formatted with commas.我想编写一个方法，它将接受一个整数并返回一个用逗号格式化的整数的std::string 。

Example declaration:示例声明：

std::string FormatWithCommas(long value);

Example usage:示例用法：

std::string result = FormatWithCommas(7800);
std::string result2 = FormatWithCommas(5100100);
std::string result3 = FormatWithCommas(201234567890);
// result = "7,800"
// result2 = "5,100,100"
// result3 = "201,234,567,890"

What is the C++ way of formatting a number as a string with commas?用逗号将数字格式化为string的 C++ 方法是什么？

(Bonus would be to handle double s as well.) （额外的好处是也可以处理double 。）

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解决方案：

参考： https://stackoom.com/en/question/UX2A

来源：https://my.oschina.net/u/4428122/blog/5403587