c++ - CIN validation using cin.fail -

i developing small program asks 4 integers 1 after other using std::cin. using function request integers, , passing in maximum value allowed argument. check if the value integer use std::cin.fail. code calls functions shown below.

    cout << "specify source number (1 - 1024)\n";     source = validate(1024);     cout << "specify destination number (1 - 1024)\n";         // except data, value equal value returned validate function     destination = validate(1024);                              // maximum possible value passed in argument in each of cases.     cout << "specify type number (1 - 10)\n";                  // user  prompted enter desired values.     type = validate(10);     cout << "source port number (1 - 1024)\n";     port = validate(1024); 

and validate function code shown below.

int validate(int max) {  int value;                                  // initialise variable hold value.  (;;) {                                  // loop forever until correct input entered.     cin >> value;      if (cin.fail()) {                // if cin fails receive value matching declared data type.         cout << "characters not permitted.\n";          // notify user of error.         cin.clear();                    // clear error flag within cin.         cin.ignore(10000,'\n');         // ignore newline character in buffer prevent infinite loop.         }     else if (value > max || value == 0) {         cout << "the value have entered not valid, please enter number between 1 , " << max << "\n";         cin.clear();                    // clear error flag within cin.         cin.ignore(10000, '\n');        // ignore newline character in buffer prevent infinite loop.     }     else         break;     } return value;                           // return validated value. } 

this works fine if user enters integer, or letter, validates should, problem having if user enters instance 34d or 22p. error saying characters not permitted exits function , moves onto next request.

tried rearranging , sorts cant seem solve it. appreciated

what want ignore rest of line if successful:

int validate(int max) {  int value;                                  // initialise variable hold value.  (;;) {                                  // loop forever until correct input entered.     cin >> value;      if (cin.fail()) {                // if cin fails receive value matching declared data type.         cout << "characters not permitted.\n";          // notify user of error.         cin.clear();                    // clear error flag within cin.         cin.ignore(10000,'\n');         // ignore newline character in buffer prevent infinite loop.         }     else if (value > max || value == 0) {         cout << "the value have entered not valid, please enter number between 1 , " << max << "\n";         cin.clear();                    // clear error flag within cin.         cin.ignore(10000, '\n');        // ignore newline character in buffer prevent infinite loop.     }     else {         cin.ignore(10000, '\n');        // ignore newline character in                     break;     } } return value;                           // return validated value. } 

if think repetitive, can like:

struct ignore_till_eol {   ignore_till_eol(std::istream& cin): input(cin) {}   ~ignore_till_eol() { input.clear(); input.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); }   std::istream& input; };  int validate(int max_value) {   for(;;) {     ignore_till_eol ignore(cin);     int v;     if( cin >> v && 0 < v && v <= max_value ) return v;     if( cin )         cout << "value invalid, must between 1 , " << max_value << "\n";     else         cout << "invalid characters in input\n";   } } 

or

int validate(int max_value) {   for(;;) {     ignore_till_eol ignore(cin);     int v;     if( !(cin >> v) )         cout << "invalid characters in input\n";     else if( 0 < v && v <= max_value )         return v;     else         cout << "value invalid, must between 1 , " << max_value << "\n";   } }