atoi的C++實現

//支持32位下利用除法的溢出判定

class Solution
{
public:
    string trim(string s)
    {
        if (s.empty())
        {
            return s;
        }
        s.erase(0, s.find_first_not_of(" "));
        s.erase(s.find_last_not_of(" ") + 1);
        return s;
    }
    int myAtoi(string str)
    {
        str = trim(str);
        int i = 0;
        bool flag = true;
        if (str[0] == '-')
        {
            flag = false;
            i = 1;
        }
        else if (str[0] == '+')
        {
            i = 1;
        }
        int sum = 0;
        for (; i < str.size(); i++)
        {
            if (isdigit(str[i]) == false)
                break;
            if (!flag)
            {
                if (INT32_MIN / (-10) < sum || (INT32_MIN / (-10) == sum && str[i] - '0' >= 8))
                {
                    return INT32_MIN;
                }
            }
            else
            {
                if (INT32_MAX / (10) < sum || (INT32_MAX / (10) == sum && str[i] - '0' >= 7))
                {
                    return INT32_MAX;
                }
            }
            sum *= 10;
            sum += str[i] - '0';
        }
        return flag ? sum : -sum;
    }
};