leetcode8 字符串转换整数

class Solution {
public:
    int myAtoi(string str) {
        long long ret=0;
        long long cmp1=((long long)1<<31)-1;
        long long cmp2=-cmp1-1;
        int i=0;
        int flag=0;
        while(i!=str.length())
        {
            if(str[i]==‘ ‘){
                i++;}
            else if(str[i]!=‘-‘&&!isdigit(str[i])&&str[i]!=‘+‘){
                return 0;}
            else
            {
                if(isdigit(str[i]))
                    flag=1;
                else if(i<str.length()-1&&isdigit(str[i+1]))
                    flag=str[i]==‘+‘?1:-1;
                else
                    return 0;
                if(!isdigit(str[i]))
                    i++;
                while(i<str.length()&&isdigit(str[i]))
                    {
                        ret=ret*10+(str[i]-‘0‘);
                        if(ret>=cmp1&&(flag==1))
                            return cmp1;
                        else if(ret>cmp1)
                            return cmp2;
                        i++;
                    }
                    return flag==1?ret:-ret;
            }         
        }
                return 0;
    }
};