Dave's Brain

Browse - programming tips - fast ascii to int

Date: 2008feb4
Language: C/C++

Q.  Is there something faster than atoi() for converting ASCII to integers?
    

A.  Yes, these functions do the trick.

// To convert a 1 digit ASCII number into an integer
inline int AsciiToInt(const char c)
{
	return c - '0';	// Yes, its that easy
}

// To convert a 2 digit ASCII number into an integer
inline int AsciiToIntTwoDigits(const char s[2])
{
	return AsciiToInt(*s) * 10 + AsciiToInt(s[1]);
}

// To convert any length ASCII number into an integer
inline int AsciiToInt(const char *p)
{
	int	result = 0;
	int	sign = 1;

	// support negative
	if (*p == '-')
	{
		sign = -1;
		p++;
	}

	for (; *p; p++)
	{
		result = result * 10 + AsciiToInt(*p);
  	}

	return sign * result;
}

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