showpoint

Showpoint is a manipulator in the C++ iostreams library that controls how floating-point values are formatted during output. It operates by setting the showpoint format flag on the stream, which affects subsequent output operations.

When enabled, showpoint causes the decimal point to be written for floating-point values, and trailing zeros are added as needed to satisfy the stream’s precision. The behavior applies to floating-point types such as float, double, and long double; integers are not affected by showpoint. The exact number of digits after the decimal depends on the stream’s precision and other formatting flags.

Showpoint is defined in the <iomanip> header as std::showpoint and can be disabled with std::noshowpoint. It interacts with other formatting controls, including std::setprecision, std::fixed, and std::scientific. In the default float format, precision governs the total number of significant digits; with fixed or scientific formatting, precision governs the number of digits after the decimal, and showpoint ensures a decimal point is present regardless.

Usage examples typically combine showpoint with other manipulators. For example, using std::cout << std::showpoint << std::setprecision(6) << 3.0; will produce an output that includes a decimal point and trailing zeros in accordance with the stream’s precision.

In summary, showpoint provides a way to explicitly display a decimal point and trailing zeros for floating-point output, ensuring a consistent representation across different values and formatting configurations.