floating point literal

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

C++ language

General topics
Preprocessor Comments Keywords	ASCII chart Escape sequences History of C++
Flow control
Conditional execution statements
if statement	switch statement
Iteration statements
for loop range-for loop (C++11)	while loop do-while loop
Jump statements
continue statement break statement	goto statement return statement
Functions
function declaration
lambda function declaration
function template
inline specifier
exception specifications (deprecated)
noexcept specifier (C++11)
Exceptions
throw expression	try-catch block
Namespaces
namespace declaration	namespace aliases
Types
fundamental types compound types enumeration types	union types function types
decltype specifier (C++11)
Specifiers
cv specifiers
storage duration specifiers
constexpr specifier (C++11)
auto specifier (C++11)
alignas specifier (C++11)
Initialization
default initialization value initialization zero initialization copy initialization direct initialization	aggregate initialization list initialization (C++11) constant initialization reference initialization

Literals
integer literals character literals floating-point literals string literals	boolean literals nullptr (C++11) user-defined (C++11)
Expressions
value categories order of evaluation	operators operator precedence
alternative representations
Utilities
Types
typedef declaration
type alias declaration (C++11)
attributes (C++11)
Casts
implicit conversions
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-style and functional cast
Memory allocation
new expression	delete expression
Classes
class declaration this pointer access specifiers	friend specifier initializer lists
Class-specific function properties
virtual function override specifier (C++11) final specifier (C++11)	explicit (C++11) static
Special member functions
default constructor copy constructor move constructor (C++11)	copy assignment move assignment (C++11) destructor
Templates
class template
function template
template specialization
parameter packs (C++11)
Miscellaneous
Inline assembly

 

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

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

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