std::atof(3)

NAME
std::atof - std::atof

Synopsis
   Defined in header <cstdlib>
   double atof( const char *str );
   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)
                        (since C++11)
     * 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

Parameters
   str - pointer to the null-terminated byte string to be interpreted

Return value
   double value corresponding to the contents of str on success. If the converted value
   falls out of range of the return type, the return value is undefined. If no
   conversion can be performed, 0.0 is returned.

Example
// Run this code
 #include <cstdlib>
 #include <iostream>
 int main()
 {
     std::cout << std::atof("0.0000000123") << '\n'
               << std::atof("0.012") << '\n'
               << std::atof("15e16") << '\n'
               << std::atof("-0x1afp-2") << '\n'
               << std::atof("inF") << '\n'
               << std::atof("Nan") << '\n'
               << std::atof("invalid") << '\n';
 }

Output:
 1.23e-08
 0.012
 1.5e+17
 -107.75
 inf
 nan
 0

See also
   stof
   stod
   stold converts a string to a floating point value
   (C++11) (function)
   (C++11)
   (C++11)
   strtof converts a byte string to a floating point value
   strtod (function)
   strtold
   from_chars converts a character sequence to an integer or floating-point value
   (C++17) (function)
   atoi
   atol converts a byte string to an integer value
   atoll (function)
   (C++11)