判断一个IP是否有效（牛客网通过正确）

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#include <iostream> #include <stdio.h> using namespace std; bool ValidIpAddr(char const * str) { int n, ip1, ip2, ip3, ip4; char dummy; bool valid = true; n = sscanf(str, "%3d.%3d.%3d.%3d%1c", &ip1, &ip2, &ip3, &ip4, &dummy); if (n != 4 || ((ip1 < 0) || (ip1 > 0xff)) || ((ip2 < 0) || (ip2 > 0xff)) || ((ip3 < 0) || (ip3 > 0xff)) ||((ip4 < 0) || (ip4 > 0xff))) { valid = false; } return valid; } int main() { string str; while(cin>>str) { if(ValidIpAddr(str.c_str())) cout<<"YES"<<endl; else cout<<"NO"<<endl; } return 0;   }