floating point literal

 

C++

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Technical Specifications

 

C++ language

 

Expressions

General

value categories (lvalue, rvalue, xvalue)

order of evaluation (sequence points)

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Literals

integer literals

floating-point literals

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null pointer literal(C++11)

user-defined literal(C++11)

Operators

Assignment operators: a=b, a+=b, a-=b, a*=b, a/=b, a%=b, a&=b, a|=b, a^=b, a<<=b, a>>=

Increment and decrement: ++a, --a, a++, a--

Arithmetic operators: +a, -a, a+b, a-b, a*b, a/b, a%b, ~a, a&b, a|b, a^b, a<<b, a>>b

Logical operators: a||b, a&&b, !a

Comparison operators: a==b, a!=b, a<b, a>b, a<=b, a>=b

Member access operators: a[b], *a, &a, a->b, a.b, a->*b, a.*b

Other operators: a(...), a,b, (T)a, a?b:c

Alternative representations of operators

Precedence and associativity

Fold expression(C++17)

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alignof

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typeid

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Operator overloading

Conversions

Implicit conversions

const_cast

static_cast

reinterpret_cast

dynamic_cast

Explicit conversions (T)a, T(a)

User-defined conversion

 

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

Syntax

A 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

Optional single quotes(') can be inserted between the digits as a separator, they are ignored when compiling.

(since C++14)

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

Run this code

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

Output:

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