NAME¶

std::stof,std::stod,std::stold - std::stof,std::stod,std::stold

Synopsis¶

Defined in header <string>
float stof ( const std::string& str, std::size_t* pos = (1) (since C++11)
nullptr );
float stof ( const std::wstring& str, std::size_t* pos = (2) (since C++11)
nullptr );
double stod ( const std::string& str, std::size_t* pos = (3) (since C++11)
nullptr );
double stod ( const std::wstring& str, std::size_t* pos = (4) (since C++11)
nullptr );
long double stold( const std::string& str, std::size_t* pos = (5) (since C++11)
nullptr );
long double stold( const std::wstring& str, std::size_t* pos = (6) (since C++11)
nullptr );

Interprets a floating point value in a string str.

Let ptr be an internal (to the conversion functions) pointer of type char* (1,3,5)
or wchar_t* (2,4,6), accordingly.

1) Calls std::strtof(str.c_str(), &ptr).
2) Calls std::wcstof(str.c_str(), &ptr).
3) Calls std::strtod(str.c_str(), &ptr).
4) Calls std::wcstod(str.c_str(), &ptr).
5) Calls std::strtold(str.c_str(), &ptr).
6) Calls std::wcstold(str.c_str(), &ptr).

Function discards any whitespace characters (as determined by std::isspace) until
first non-whitespace character is found. Then it takes as many characters as
possible to form a valid floating-point representation and converts them to a
floating-point value. The valid floating-point value can be one of the following:

* decimal floating-point expression. It consists of the following parts:

* (optional) plus or minus sign
* nonempty sequence of decimal digits optionally containing decimal-point
character (as determined by the current C locale) (defines significand)
* (optional) e or E followed with optional minus or plus sign and nonempty
sequence of decimal digits (defines exponent to base 10)
* hexadecimal floating-point expression. It consists of the following parts:

* (optional) plus or minus sign
* 0x or 0X
* nonempty sequence of hexadecimal digits optionally containing a decimal-point
character (as determined by the current C locale) (defines significand)
* (optional) p or P followed with optional minus or plus sign and nonempty
sequence of decimal digits (defines exponent to base 2)
* infinity expression. It consists of the following parts:

* (optional) plus or minus sign
* INF or INFINITY ignoring case
* not-a-number expression. It consists of the following parts:

* (optional) plus or minus sign
* NAN or NAN(char_sequence) ignoring case of the NAN part. char_sequence can only
contain digits, Latin letters, and underscores. The result is a quiet NaN
floating-point value.
* any other expression that may be accepted by the currently installed C locale

If pos is not a null pointer, then ptr will receive the address of the first
unconverted character in str.c_str(), and the index of that character will be
calculated and stored in *pos, giving the number of characters that were processed
by the conversion.

Parameters¶

str - the string to convert
pos - address of an integer to store the number of characters processed

Return value¶

The string converted to the specified floating point type.

Exceptions¶

std::invalid_argument if no conversion could be performed.

std::out_of_range if the converted value would fall out of the range of the result
type or if the underlying function (std::strtof, std::strtod or std::strtold) sets
errno to ERANGE.

Example¶

This section is incomplete
Reason: no example

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
std::out_of_range would not be thrown
LWG 2009 C++11 if the converted will throw
value would fall out of the range of
the result type
LWG 2403 C++11 stof called std::strtod or std::wcstod stof calls std::strtof or
std::wcstof

See also¶

stoi
stol
stoll converts a string to a signed integer
(C++11) (function)
(C++11)
(C++11)
stoul
stoull converts a string to an unsigned integer
(C++11) (function)
(C++11)
from_chars converts a character sequence to an integer or floating-point value
(C++17) (function)

Category:¶

* Todo no example