LeetCode之String to Integer(atoi)

class Solution {
public:
int myAtoi(string str) {
int sign(1);
int i(0), len = str.size();
long long value(0);
while(i < len && str[i] == ' ') ++i;

if(i < len && str[i] == '-') {
sign = -1;
++i;
}
else if(i < len && str[i] == '+') ++i;

while(i < len){
if(str[i] >= '0' && str[i] <= '9'){
value = value*10 + (str[i] - '0');
++i;
if(sign > 0 && value > INT_MAX) return INT_MAX;
else if(sign < 0 && -value < INT_MIN) return INT_MIN;
}
else break;
}
return value * sign;
}
};