std::strtof, std::strtod, std::strtold

 

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Functions
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isalnum isalpha islower isupper isdigit isxdigit	isblank (C++11) iscntrl isgraph isspace isprint ispunct
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tolower	toupper
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atof atoiatolatoll (C++11) strtolstrtoll (C++11)	strtoulstrtoull (C++11) strtofstrtodstrtold (C++11)(C++11) strtoimaxstrtouimax (C++11)(C++11)
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Defined in header <cstdlib>
float       strtof (constchar* str, char** str_end );	(1)	(since C++11)
double      strtod (constchar* str, char** str_end );	(2)
longdouble strtold(constchar* str, char** str_end );	(3)	(since C++11)

Interprets a floating point value in a byte string pointed to by str.

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.

(since C++11)

• any other expression that may be accepted by the currently installed C locale.

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is a null pointer, it is ignored.

Parameters

str	-	pointer to the null-terminated byte string to be interpreted
str_end	-	pointer to a pointer to character.

Return value

Floating point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, ​0​ is returned and *str_end is set to str.

Example

Run this code

#include <cerrno>#include <clocale>#include <cstdlib>#include <iostream>#include <string>   int main(){constchar* p ="111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz";char* end{};std::cout<<"Parsing \""<< p <<"\":\n";errno=0;for(double f = std::strtod(p, &end); p != end; f = std::strtod(p, &end)){std::cout<<" '"<<std::string(p, end - p)<<"' -> "; p = end;if(errno==ERANGE){std::cout<<"range error, got ";errno=0;}std::cout<< f <<'\n';}   if(std::setlocale(LC_NUMERIC, "de_DE.utf8")){std::cout<<"With de_DE.utf8 locale:\n";std::cout<<" '123.45' -> "<< std::strtod("123.45", 0)<<'\n';std::cout<<" '123,45' -> "<< std::strtod("123,45", 0)<<'\n';}}

Possible output:

Parsing "111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz": '111.11' -> 111.11 ' -2.22' -> -2.22 ' 0X1.BC70A3D70A3D7P+6' -> 111.11 ' -Inf' -> -inf ' 1.18973e+4932' -> range error, got inf With de_DE.utf8 locale: '123.45' -> 123 '123,45' -> 123.45

See also

atof	converts a byte string to a floating point value (function)
wcstofwcstodwcstold	converts a wide string to a floating-point value (function)
from_chars (C++17)	converts a character sequence to an integer or floating-point value (function)
C documentation for strtof, strtod, strtold