leetcode 8

class Solution {
public:
    int myAtoi(string str) {
        int base=0;
        int sign=1;
        int i=0;
        while(str[i]=' ') 
            i++;
        //judge sign
        if(str[i]=='+') {
            sign=1; 
            i++;
        }
        if(str[i]=='-') {
            sign=-1; 
            i++;
        }
        while(str[i]>='0'&&str[i]<='9'){
            //judge overflow
            if((base>214748364)||(base==214748364&&((str[i]-'0')>7){
                if(sign==1) 
                    return 2147483647;
                else 
                    return -2147483648;
            }
            base=base*10+(str[i++]-'0');
        }
        return base*sign;
};

首先解决空格
接着解决符号
然后判断数字，解决非法输入
判断溢出