{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, 0x7FFFFFFFtest("+2147483647", 2147483647, true);test("+2147483648", 0, false);//有效的最小负整数, 0x80000000test("-2147483648", -2147483648, true);test("-2147483649", 0, false);return 0;}