String to Integer(atoi)

C language

int len = strlen(str);
int i = 0;
const int MAX_POS = 2147483647;
const int MAX_NEG = -2147483648;
int sign = 1;
int max = MAX_POS;
int rval = 0;

while (str[i] == ' ' && i<len)
    i++;

if (str[i] == '-') {
    sign = -1;
    max = MAX_NEG;
}

if (str[i] == '-' || str[i] == '+')
    i++;

for (; i<len; i++) {
    if (str[i] < '0' || str[i] > '9')
        break;
    // handle the out of range
    if (((max - (str[i] - '0')*sign) / 10)*sign >= rval)
        rval = rval*10 + str[i] - '0';
    else
        return max;
}

• obstace: The value is out of the range of representable values