floating point literal

Floating point literal defines a compile-time constant whose value is specified in the source file.

Syntax

Floating-point literals have two syntaxes. The first one consists of the following parts:

• nonempty sequence of decimal digits containing a decimal point character (defines significand)
• (optional) e or E followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
• (optional) a suffix type specifier as a l, f, L or F

The second one consists of the following parts:

• nonempty sequence of decimal digits (defines significant)
• e or E followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
• (optional) a suffix type specifier as a l, f, L or F

The suffix type specifier defines the actual type of the floating-point literal:

• (no suffix) defines double
• f F defines float
• l L defines long double

Explanation

A decimal scientific notation is used, meaning that the exponent is the power of 10 by which the significant is multiplied.
The mathematical meaning of 123e4 is 123×10⁴.

Example

#include <iostream>
int main()
{
  std::cout << 123.456e-67 << '\n'
            << .1E4f       << '\n'
            << 58.         << '\n'
            << 4e2         << '\n';
}

1.23456e-65
1000
58
400

Notes

The hexadecimal floating-point constants (e.g. 0x1p-5, 0x1.0Ap-2, 0x1.8p-1), which are allowed in the C programming language, cannot be used as floating point literals in C++ (although some C++ compilers might interpret them). However, they may be parsed and printed by the I/O functions: both C++ I/O streams when std::hexfloat is enabled and the C I/O streams: std::printf, std::scanf, etc. See std::strtof for the format description.