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

Formatting Numbers with Commas in C

Introduction:

In C , formatting numbers with commas is a common task, especially when displaying currency or large numerical values. This tutorial demonstrates an efficient method for adding commas to integers and doubles.

Method:

To format numbers with commas, we will utilize std::locale and std::stringstream.

Step 1: Using std::locale

<code class="cpp">std::stringstream ss;
ss.imbue(std::locale(""));</code>

std::locale allows us to set the locale for string formatting. Using the empty string ("") ensures that the locale is set to the user's default system settings.

Step 2: Using std::stringstream

<code class="cpp">ss << std::fixed << value;

std::stringstream is used to construct the formatted string. We insert the value into the stream using std::fixed to maintain the decimal point.

Formatting Integers:

For integers, simply call the FormatWithCommas() method as follows:

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

Formatting Doubles:

For doubles, use the same method but with a slight modification in the usage of std::fixed:

<code class="cpp">ss << std::fixed << std::setprecision(2) << value;

std::setprecision() ensures that only two decimal digits are displayed.

Example Usage:

<code class="cpp">#include <cmath>

std::string FormatWithCommas(double value)
{
    std::stringstream ss;
    ss.imbue(std::locale(""));
    ss << std::fixed << std::setprecision(2) << value;
    return ss.str();
}

int main()
{
    double pi = std::atan(1.0) * 4.0;
    std::string result = FormatWithCommas(pi);
    std::cout << result << "\n";
}</code>

Output:

3.14

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