Function Keys (F1-F12) Encountered a logic bug

[vladeoff]

Hello again,

I was developing an exercise program for myself (note: not a project in school) to enhance my programming skills in C++ then I encountered a "logic bug" (that's how I call it :D ) I think. I googled stuffs I need to know and ended up to post my question here.

Here's the scene:

1. When using GetAsyncKeyState I can capture Function Keys [F1-F12, etc..]
2. While doing and having fun to my exercise program, I suddenly noticed that whatever key I pressed from the keyboard {example: asdfkj], it keeps the keys entered and brings to a "field" that accepts user input.



What you should do...

1. Press any key (example: asdfisdjfisdjff) then proceed to press F1. And see what happens. I don't know how to erase what I have entered before pressing F1. Hope someone could help me.

Please refer to line #96 - #105 only. TIA

here's the code.

#include <cstdlib>
#include <iostream>
#include <windows.h>
#include <string>

using namespace std;

void gotoxy();
void gotoxy( int column, int line ) {

  COORD coord;
  coord.X = column;
  coord.Y = line;
  SetConsoleCursorPosition(GetStdHandle( STD_OUTPUT_HANDLE ), coord );
}

void clearstatus();
void clearstatus() {

    for(int x=3;x<=38;x++) {
        gotoxy(x,10); 
        cout << " ";
    }
}

void newstudent();
void newstudent(){

     string in;
     
     for(int x=4;x<=10;x++)
     {
        gotoxy(34,x);
        cout << "|";
        gotoxy(76,x);
        cout << "|";                  
     }
     gotoxy(35,3);
     cout << "---------------NEW STUDENT---------------";
     gotoxy(36,4);
     cout << "Full Name : ";
     gotoxy(36,5);
     cout << "   Course : ";
     gotoxy(36,6);
     cout << "    Level : ";
     gotoxy(36,7);
     cout << " Contact# : ";
     gotoxy(35,8);
     cout << "-----------------------------------------";
     gotoxy(48,4); 
     getline(cin, in);
     gotoxy(48,5); 
     getline(cin, in);
     gotoxy(48,6); 
     getline(cin, in);
     gotoxy(48,7); 
     getline(cin, in);
     
     gotoxy(36,9);
     cout << "Do you want to keep the record? [Y/N]-";
     getline(cin,in);

     gotoxy(80/2-(24/2),18);
     cout << "----CONSOLE MESSAGE----";
     gotoxy(80/2-(24/2),20);
     cout << "-----------------------";
     
     if(in=="y" || in=="Y") {
          gotoxy(80/2-(17/2), 19);
          cout << "RECORD IS SAVED." << endl;
     }
     else if(in=="n" || in=="N") {
          gotoxy(80/2-(22/2), 19);
          cout << "RECORD WAS DISCARDED." << endl;
     }
}

//*********************************
//*********************************

int main(int argc, char *argv[])
{
   start:
   
   gotoxy(3, 4);
   cout << "[F1]--New Student Record";
   gotoxy(3, 5);
   cout << "[F2]--Students Class Schedules";
   gotoxy(3, 6);
   cout << "[F3]--Medical Check-up History";
   gotoxy(3, 7);
   cout << "[F4]--Find Student Record";
   gotoxy(3, 8);
   cout << "[F5]--Quit Program";
   
   while(1)
   {
       if(GetAsyncKeyState(0x70))
       {
           clearstatus();
           gotoxy(3,10);     
           cout << "Status: New Record (F1)" << endl;
           newstudent();
           break;
       }
       else if(GetAsyncKeyState(0x71)) {
           clearstatus();
           gotoxy(3,10); 
           cout << "Status: Class Schedule (F2)" << endl;
       }
       else if(GetAsyncKeyState(0x72)) {
           clearstatus();
           gotoxy(3,10); 
           cout << "F3 was hit" << endl;
       }
       else if(GetAsyncKeyState(0x73)) {
           clearstatus();
           gotoxy(3,10); 
           cout << "F4 was hit" << endl;
       }
       else if(GetAsyncKeyState(0x74)) {
           clearstatus();
           gotoxy(3,10); 
           cout << "F5 was hit" << endl;
       }
       else if(GetAsyncKeyState(0x1B)) {
           clearstatus();
           gotoxy(3,10); 
           cout << "ESC was hit" << endl;
           break;
       }
       else {
           Sleep(10);     
       }
   }
    
        gotoxy(25, 22);
    system("PAUSE");
    
    for(int x=3;x<=38;x++) {
        gotoxy(x,10); 
        cout << " ";
    }
    
    for(int x=4;x<=10;x++) {
            gotoxy(34,x);
            cout << " ";
            gotoxy(76,x);
            cout << " ";                  
         }
         
    for(int x=35;x<=77;x++) {
        for(int y=3;y<=10;y++) {
                gotoxy(x,y);     
                cout << " ";
        }
    }
    
    for(int x=80/2-(32/2);x<=((80/2)-(32/2)+32);x++) {
        for(int y=18;y<=22;y++) {
                gotoxy(x,y);
                cout << " ";
        }
    }
    
    goto start;
    
    return EXIT_SUCCESS;
}

[MiiNiPaa]

Try calling std::cin.sync(); before reading input. The behavior is implementation defined, but on MSVS and mingw gcc it does what you want

[cire]

You're mixing buffered input with reading key states. No big surprise there are issues.

Don't do that. If you must do that, you should probably be tackling it at a different level:

void newstudent(){

    auto std_in = GetStdHandle(STD_INPUT_HANDLE);
    FlushConsoleInputBuffer(std_in);

    for (int x = 4; x <= 10; x++)
    {
        gotoxy(34, x);
        cout << "|";
        gotoxy(76, x);
        cout << "|";
    }
    gotoxy(35, 3);
    cout << "---------------NEW STUDENT---------------";
    gotoxy(36, 4);
    cout << "Full Name : ";
    gotoxy(36, 5);
    cout << "   Course : ";
    gotoxy(36, 6);
    cout << "    Level : ";
    gotoxy(36, 7);
    cout << " Contact# : ";
    gotoxy(35, 8);
    cout << "-----------------------------------------";
    gotoxy(48, 4);

    char buffer[256];
    DWORD dummy;

    ReadFile(std_in, buffer, 256, &dummy, 0);
    gotoxy(48, 5);
    ReadFile(std_in, buffer, 256, &dummy, 0);

    gotoxy(48, 6);
    ReadFile(std_in, buffer, 256, &dummy, 0);
    gotoxy(48, 7);
    ReadFile(std_in, buffer, 256, &dummy, 0);

    gotoxy(36, 9);
    cout << "Do you want to keep the record? [Y/N]-";
    ReadFile(std_in, buffer, 256, &dummy, 0);

    gotoxy(80 / 2 - (24 / 2), 18);
    cout << "----CONSOLE MESSAGE----";
    gotoxy(80 / 2 - (24 / 2), 20);
    cout << "-----------------------";

    char ch = buffer[0] ;
    if (ch == 'y' || ch == 'Y') {
        gotoxy(80 / 2 - (17 / 2), 19);
        cout << "RECORD IS SAVED." << endl;
    }
    else if (ch == 'n' || ch == 'N') {
        gotoxy(80 / 2 - (22 / 2), 19);
        cout << "RECORD WAS DISCARDED." << endl;
    }
}

[vladeoff]

Hi again..thank you for your input..I tried your code cire.. and here are the result.

auto std_in = GetStdHandle(STD_INPUT_HANDLE);

error1: 28 D:\cplusplus\main.cpp ISO C++ forbids declaration of `std_in' with no type

error2: 28 D:\cplusplus\main.cpp invalid conversion from `void*' to `int'

FlushConsoleInputBuffer(std_in);

error1: 29 D:\cplusplus\main.cpp invalid conversion from `int' to `void*'

ReadFile(std_in, buffer, 256, &dummy, 0);

error1: 55 D:\cplusplus\main.cpp initializing argument 1 of `BOOL ReadFile(void*, void*, DWORD, DWORD*, _OVERLAPPED*)'

FYI: I am using the DevC++ by Bloodshed.. version is 4.9.9.2 for the code you've written.

I also tried the code in VS10.. and it works! :) :)

btw..is there anyway I can make it run in DevC++? Thank you very much, you helped a lot. God bless you. :)

[giblit]

IDE doesn't really affect it. The compiler and compiler settings does. Basically you can either enable c++11 -std=c++11 or tell it the data types instead of using auto which is a type deducter. http://www.cplusplus.com/doc/tutorial/variables/

I would assume the type would be something along the lines of HANDLE but I am not positive since I don't use windows api.

[vladeoff]

My next problem to the above code solution is that how should I
Echo the text to screen from ReadFile since I use getline.. :-( anybody?