Convert string to double

Parses the C string str interpreting its content as a floating point number and returns its value as a double.

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes as many characters as possible that are valid following a syntax resembling that of floating point literals, and interprets them as a numerical value. The rest of the string after the last valid character is ignored and has no effect on the behavior of this function.

A valid floating point number for atof is formed by a succession of:

• An optional plus or minus sign
• A sequence of digits, optionally containing a decimal-point character
• An optional exponent part, which itself consists on an 'e' or 'E' character followed by an optional sign and a sequence of digits.

If the first sequence of non-whitespace characters in str does not form a valid floating-point number as just defined, or if no such sequence exists because either str is empty or contains only whitespace characters, no conversion is performed.

Syntax

double atof(const char *str)

Parameters

• str C string beginning with the representation of a floating-point number.

Return Value

On success, the function returns the converted floating point number as a double value. If no valid conversion could be performed, or if the correct value would cause underflow, a zero value (0.0) is returned.

If the correct value is out of the range of representable values, a positive or negative HUGE_VAL is returned.