Floating-point literal

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

Syntax

decimal-exponent has the form

hex-exponent has the form

exponent-sign , if present, is either + or -

suffix , if present, is one of f , l , F , L , f16 , f32 , f64 , f128 , bf16 , F16 , F32 , F64 , F128 , BF16 (since C++23) . The suffix determines the type of the floating-point literal:

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

Explanation

Decimal scientific notation is used, meaning that the value of the floating-point literal is the significand multiplied by the number 10 raised to the power of decimal-exponent . E.g. the mathematical meaning of 123e4 is 123×10 ⁴ .

Notes

The hexadecimal floating-point literals were not part of C++ until C++17, although they can be parsed and printed by the I/O functions since C++11: 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.

Example

#include <iomanip>
#include <iostream>
#include <limits>
#include <typeinfo>
#define OUT(x) '\n' << std::setw(16) << #x << x
int main()
{
    std::cout
        << "Literal" "\t" "Printed value" << std::left
        << OUT( 58.            ) // double
        << OUT( 4e2            ) // double
        << OUT( 123.456e-67    ) // double
        << OUT( 123.456e-67f   ) // float, truncated to zero
        << OUT( .1E4f          ) // float
        << OUT( 0x10.1p0       ) // double
        << OUT( 0x1p5          ) // double
        << OUT( 0x1e5          ) // integer literal, not floating-point
        << OUT( 3.14'15'92     ) // double, single quotes ignored (C++14)
        << OUT( 1.18e-4932l    ) // long double
        << std::setprecision(39)
        << OUT( 3.4028234e38f  ) // float
        << OUT( 3.4028234e38   ) // double
        << OUT( 3.4028234e38l  ) // long double
        << '\n';
    static_assert(3.4028234e38f == std::numeric_limits<float>::max());
    static_assert(3.4028234e38f ==  // ends with 4
                  3.4028235e38f);   // ends with 5
    static_assert(3.4028234e38 !=   // ends with 4
                  3.4028235e38);    // ends with 5
    // Both floating-point constants below are 3.4028234e38
    static_assert(3.4028234e38f !=  // a float (then promoted to double)
                  3.4028234e38);    // a double
}

Literal         Printed value
58.             58
4e2             400
123.456e-67     1.23456e-65
123.456e-67f    0
.1E4f           1000
0x10.1p0        16.0625
0x1p5           32
0x1e5           485
3.14'15'92      3.14159
1.18e-4932l     1.18e-4932
3.4028234e38f   340282346638528859811704183484516925440
3.4028234e38    340282339999999992395853996843190976512
3.4028234e38l   340282339999999999995912555211526242304

References

See also