How to achieve precise formatting with std::ostream like printf_s?

Precise Formatting with std::ostream

How to achieve precise formatting with std::cout? Consider the following example:

<code class="cpp">double my_double = 42.0;
char str[12];
printf_s("%11.6lf", my_double); // Prints " 42.000000"</code>

In this code, printf_s is used to format and print the double my_double with specific precision and width. The equivalent functionality in std::ostream can be achieved using stream manipulators.

To output " 42.000000" using std::cout, apply these manipulators in sequence:

std::fixed: Sets fixed-point notation instead of scientific notation.

std::setw(11): Sets the width of the output field to 11 characters.

std::setprecision(6): Specifies the number of digits to be displayed after the decimal point.

The correct code becomes:

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

std::cout << std::fixed << std::setw(11) << std::setprecision(6) << my_double;</code>

This approach allows for precise formatting of double values using std::ostream without resorting to third-party libraries or custom string manipulation.

For a comprehensive reference on std::ostream formatting, refer to the C Standard Library documentation, specifically the section on "Stream Manipulators."

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