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

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

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.

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

See also

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