How to Format Floating Point Numbers with std::cout?

Formatting Floating Point Numbers with std::cout

This question addresses the challenges of formatting floating-point numbers using std::cout, a fundamental output stream in C . The user expresses frustration with the limited formatting options available through std::cout and contemplates resorting to the more verbose sprintf_s function. They seek a comprehensive reference that consolidates formatting capabilities for std::ostream.

Answer:

Fortunately, std::cout provides stream manipulators that offer flexible formatting options for floating-point numbers. These manipulators include:

• std::fixed: Specifies fixed-point notation instead of scientific notation.
• std::setw(width): Sets the field width for the output, padding to the left or right with spaces.
• std::setprecision(precision): Controls the number of digits after the decimal point.
• std::setfill(character): Fills any empty spaces within the field with the specified character.

Example:

The desired output of " 42.000000" can be achieved using the following code:

<code class="cpp">#include <iomanip>
std::cout << std::fixed << std::setw(11) << std::setprecision(6) << my_double;</code>

Additional Notes:

• The manipulator std::fixed ensures that the number is formatted with a fixed number of decimal places.
• The manipulators std::setw and std::setprecision control the field width and precision, respectively.
• The manipulator std::setfill can be used to fill the empty spaces with zeros or any other desired character.

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