{面试题49} 把字符串转换成整数

From 剑指Offer 何海涛 著

#include <iostream>
#include <string>
#include <cctype>

bool g_valid = false;

int StrToInt(const std::string& s) {
    long long res = 0ll;
    int n = s.size();
    int i= 0;
    g_valid = true;
    while(i<n && s[i] == ' ') {
        i++;
    }
    bool isNegative = false;
    if(s[i] == '-') {
        isNegative = true;
        i++;
    } else if(s[i] == '+') {
        i++;
    }
    if(i== n) {
        g_valid = false;
        return res;
    }
    while(i<n && isdigit(s[i])) {
        res *= 10;
        res += s[i] - '0';
        i++;
        if(!isNegative && res > (long)0x7fffffff || isNegative&& -res < (long)0x80000000) {
            g_valid = false;
            return 0;
        }
    }
    if(i< n) {
        g_valid = false;
        return 0;
    }
    
    return isNegative ? -res : res;
}

测试集:

void test(const std::string &s, int n, bool valid) {
    std::cout << std::boolalpha<< (StrToInt(s) == n && valid == g_valid) << std::endl;
}

int main(int argc, char* argv[]) {

    test("", 0, false);
    test("  ", 0, false);
    
    test("+", 0, false);
    test("-", 0, false);

    test("123", 123, true);
    test("+0", 0, true);
    test("-0", 0, true);
    test("+123", 123, true);
    test("-123", -123, true);
    
    test("abc", 0, false);
    test("1a33", 0, false);
    
    //有效的最大正整数, 0x7FFFFFFF
    test("+2147483647", 2147483647, true);
    test("+2147483648", 0, false);
    
    //有效的最小负整数, 0x80000000
    test("-2147483648", -2147483648, true);
    test("-2147483649", 0, false);

    return 0;
}