String conversion to numeric value functions.

• atof, _wtof converts a character string to a double value
• atoi, _wtoi converts a character string to an integer value
• atol, _wtol converts a character string to a long integer value
• atoll, _wtoll convers a character string to a long long integer value

#include <math.h>
#include <stdlib.h>

double atof(const char *string);
int atoi(const char *string);
long atol(const char *string);
long long atoll(const char *string);

#include <wchar.h>

double _wtof(const wchar_t *string);
int _wtoi(const wchar_t *string);
long _wtol(const wchar_t *string);
long long _wtoll(const wchar_t *string);

Parameters

string

A sequence of characters that represent a numerical value of the specified type. The maximum string size for atof and _watof is 100 characters.

Remarks

These functions stop reading the input string at the first character not recognizable as part of a number. This character may be the null character \0 terminating the string.

atof (and _wtof) expects the string to have this form:

[whitespace][sign]{[digits]|[.digits]}[d|D|e|E[sign]digits]

Where:

whitespace

Space and/or tab characters, which are ignored.

sign

Either plus (+) or minus (-).

digits

Decimal digits. If no digits appear before the decimal point, at least one must appear after it. There may be an exponent, which is an introductory letter (d, D, e, or E) and an optionally signed integer.

atoi, atol and atoll (and their wide-character equivalents) do not recognize decimal points or exponents. The string argument for these functions has this form:

[whitespace][sign][digits]

Where whitespace, sign, and digits are as described for atof.

Note:   Results are undefined on overflow.

Return Values

Generic Text Routines

Requirements