[leetcode 8] String to Integer (atoi)

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本文详细解析了atoi函数的实现原理，包括符号处理、数字读取、边界检查和返回值处理，旨在帮助开发者深入理解字符串转整数的过程。

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

class Solution {
public:
    int atoi(const char *str) {
        const int n = strlen(str);
        int res = 0;
        int sign = 1;
        int i = 0;
        while (i < n && str[i] == ' ') {
            i++;
        }
        if (str[i] == '-') {
            sign = -1;
            i++;
        } else if (str[i] == '+') {
            i++;
        }
        for ( ; i < n; i++) {
            if (str[i] > '9' || str[i] < '0') {
                break;
            }
            if (res > INT_MAX/10 || (res == INT_MAX/10 &&  (str[i]-'0')>INT_MAX%10)) {
                return sign>0?INT_MAX:INT_MIN;
            }
            res = res*10 + (str[i] - '0');
        }
        return sign*res;
        
    }
};