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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23) basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (DR*) basic_string::endbasic_string::cend (DR*) basic_string::rbeginbasic_string::crbegin (DR*) basic_string::rendbasic_string::crend (DR*) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Operations basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::compare basic_string::replace basic_string::replace_with_range (C++23) basic_string::substr basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)   basic_string::swap

Search basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos Deduction guides (C++17) Non-member functions operator+ swap(std::basic_string) operator""s (C++14) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) Numeric conversion stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string>hash<std::u8string> (C++11)  (C++11)(C++11)(C++11)(C++20) hash<std::pmr::string>hash<std::pmr::wstring>hash<std::pmr::u32string>hash<std::pmr::u16string>hash<std::pmr::u8string> (C++17)(C++17)(C++17)(C++17)(C++20)

 

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.

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.

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

stoistolstoll (C++11)(C++11)(C++11)	converts a string to a signed integer (function)
stoulstoull (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)