From cppreference.com
doubleatof(constchar*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
) (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
) (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
.
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>intmain(){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