C++ most efficient way to convert string to int (faster than atoi)

Question

As mentioned in the title, I\'m looking for something that can give me more performance than atoi. Presently, the fastest way I know is

atoi(mystring.c_str(         


        

Answer 1

Here's the entirety of the atoi function in gcc:

long atoi(const char *str)
{
    long num = 0;
    int neg = 0;
    while (isspace(*str)) str++;
    if (*str == '-')
    {
        neg=1;
        str++;
    }
    while (isdigit(*str))
    {
        num = 10*num + (*str - '0');
        str++;
    }
    if (neg)
        num = -num;
    return num;
 }

The whitespace and negative check are superfluous in your case, but also only use nanoseconds.

isdigit is almost certainly inlined, so that's not costing you any time.

I really don't see room for improvement here.