就是多处理一些细节东西， 提供一下我的测试数据吧。
/** -- test case: "" "abc" "01234" "0.2" "-123" "123.a" "12a23" "abc12" "-123a" "-12-" "." "+1" "-+1" "+-1" " 33" "- 33" " 003" "+ 22" " +004500" "13+-1" "123 3" "3147483647" "-3147483648" "9223372036854775809" "1234 3746813578" **/ class Solution { public: int myAtoi(string str) { int flg = 0; long long ans = 0; int len = str.length(); for(int index = 0; index < len; index++) { int num = str[index] - '0'; if(str[index] == '-' or str[index] == '+') { if(flg == 0) flg = ',' - str[index]; else break; } else if (str[index] == ' ' and flg == 0) { continue; } else if( num >= 0 && num <= 9 ) { if(flg == 0) { flg = 1; } ans = ans*10 + num; if( ans > INT_MAX ) break; } else break; } ans = ans * flg; if(ans < INT_MIN) ans = INT_MIN; else if(ans > INT_MAX) ans = INT_MAX; return ans; } };