Problems with cin and GetAsyncKeyState

Well, I'm a beginner in C++ and I tend to make MANY errors when trying out codes I'm not taught before. So recently I got to know about GetAsyncKeyState and i used it in my main function which is basically a menu. I did all the stuff I will need to do for GetAsyncKeyState in a bool keyDown(int vKey) function which returns either 1 or 0 depending on whether the key is pressed.

Now my menu is supposed to link to another file which takes care of the user entering his/her profile. For this page I used cin, but I noticed a bug. This bug is that if I type something on the menu then press Enter to go into the profile page, which would go to the void profile() function, whatever I typed while on the menu page would automatically cin into my first cin, which is very weird. Of course, it would be better if someone could add me on MSN and help me but [if you need to see a part of my code to find out whats causing this problem feel free to post it here.]

I don't do MSN, but I will try to help you here.
GetAsyncKeyState doesn't "consume" the keys that it returns as being used. You may want to use the FAQ to get the code for "how do I read input without waiting for the user" (In level 2 "How Do I ..."). That will consume the input.

However, if you want to use cin, you'd better not use Windows API functions intermingled with that.

[Of course, another option would be to count the number of keys detected with GetAsyncKeyState, and then use cin.ignore(count), but if you don't scan for EVERY key on the keyboard, you potentially will miss some - so I'd still recommend that you use a different method for reading the keyboard].

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Mats

Well basically what I meant was that the bool keyDown(int vKey) function would check if a key is pressed. So lets say keyDown(VK_RETURN) would check if VK_RETURN is pressed. So lets say I do something like

Code:

---

if(keyDown(VK_RETURN))
{
    cout << "Enter!" << endl;
}

---

the keyDown function would return true if I pressed Enter and then cout Enter right? But now the problem is the string I want the user to cin after the user is done with the menu.

Like

Code:

---

struct profile
{
    string name;
};
void profilepage(void)
{
    system("cls");
    profile player;
    cout << "Enter your name :";
    cin >> player.name;
void main (void)
{
    cout << "This is the Menu! Press Enter to proceed!" << endl;
    if(keyDown(VK_RETURN))
    {
          profilepage();
    }
}

---

So if the player presses Enter, he'll go to the "Enter your name :" part right? But the bug now is that, if I press Enter, it would show "Enter you name :" but the blinking _ is on the next line. I found it weird so at the "This is the Menu! Press Enter to proceed!" part I typed lolol before pressing Enter and the moment I press Enter it shows "Enter you name : lolol". Why does this happen? O_O and please remember that I am still a newbie so xD

Yes, so did you just skim through my reply without paying attention: GetAsyncKeyState() only tells you whether that key is pressed. If you press the key, a character is entered into the input buffer. That is what cin reads. GetAsyncKeyState does not use up the keypresses, it just reports if that key is pressed at the exact moment in time or not.

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Mats

Well I admit I skimmed through but it was because I didn't get the "consume" part so I thought I had to make things as clear as possible. So anyway, are you talking about the cin buffer thing which cin.clear() clears? and whenever I type anything it would go into the cin buffer?

Yes, I'm talking about [1] the buffer that cin uses. But cin.clear() does not empty that buffer. cin.ignore(19999) will remove anything up to the next newline (as long as it's less than 19999 characters).

And by consume, I mean that GetAsyncKeyState does not "use up" any keypresses, the keys you hit will go into the cin buffer as you type, and then be used by cin >> player.name. Try typing in "Charlie" before hitting enter on the main menu, and you would see that palyer.name becomes "Charlie".


[1] Technically, cin doesn't get any data until enter is pressed, but for all intents and purposes we can ignore that. I'm just saying this to avoid someone commenting that this is incorrect.

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Mats

Quote:

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Try typing in "Charlie" before hitting enter on the main menu, and you would see that palyer.name becomes "Charlie".

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Yep this is THE bug. How do I fix this? put cin.ignore(19999) somewhere properly in the void profile(void) function?

Quote:

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Originally Posted by In Post #2

You may want to use the FAQ to get the code for "how do I read input without waiting for the user" (In level 2 "How Do I ..."). That will consume the input.

---

.

That would consume the characters, and I _THINK_ it will be safe.

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Mats

@_@ A bunch of codes I don't understand. Lol. Umm...char pword[BUFSIZ];
BUFSIZ? What exactly is BUFSIZ? I don't see it anywhere else in the code -_-

BUFSIZ is defined by stdio.h and is the size of the FILE * buffers - it's just "some arbitrarily large number that we can expect the user to not exceed when typing". You can replace it with for example 100 or 500 if you like.

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Mats

Ahh OK. I'll try it out to see if I can fix my problem. By the way, how can I get you if I can't get other stuff or can't solve my current problem. This thread? Create another thread? xD Thanks for the help.

You should not try to "get me", you should post in a thread here - there are many other skilled people on the forum. Whether you post in this thread or a new one depends on how close the question is to the current thread. If it's not related, then a new thread is the correct thing.

You can also try to search the forum before you ask a new question.

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Mats

Ok suprisingly I solved the cin buffer thing. I added a cin.ignore(50,'\n') for it to work. Somehow, cin.ignore() and cin.ignore(50) doesn't work. Anyway, now I have a problem where if the user press Enter without keying in anything for "Enter Name :" an endless loop of the next cout would occur. "Enter Name:"'s variable is a string.

By default, ignore ignores until the EOF.

As to your question, who knows what you did? (Answer: you, and not us.) What is the loop condition on your infinite loop?

That endless loop is something like THE endless loop that happens when say you cin a char into an int variable. But if you need to see the code,
Here it is!

Code:

---

struct personProfile
{
        char name[50];
        int age;
        char gender;
};
void profile (void)
{
        int choice;
        personProfile person1;
       
        system("cls");
        cout<<"                        ~~Welcome to Black-O~~"<<endl;
        cout << endl;
                cout<<"Enter Name: ";
                cin.get(person1.name,50,'\n');
.
.
.

---

There is no loop shown in your code, so I expect the endless loop is elsewhere.

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Mats

No even in a simple code without any loops, this error will also happen.
See Cprogramming.com : FAQ > How do I...(Level 2) > Why does my program enter an infinite loop if the user inputs invalid data? (C++).
I just want to know what I should do to my code that you can see to prevent the user from entering invalid data.

Quote:

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Originally Posted by KgNe

No even in a simple code without any loops, this error will also happen.
See Cprogramming.com : FAQ > How do I...(Level 2) > Why does my program enter an infinite loop if the user inputs invalid data? (C++).
I just want to know what I should do to my code that you can see to prevent the user from entering invalid data.

---

Well, there are several approaches to "avoid user inputting invalid data" - the most common one is to read data with a fgets (in C) or getline (in C++). That way, the user can type in anything he/she likes, and the application will not misbehave. It is then up to the rest of the code to figure out if the input is valid/useful with suitable conversion functions to conver the data into the correct format - e.g. string to integer, string to date, string to limited length string [e.g. you input a line of up to 500 characters, but a "username" is only allowed to be 30 characters].

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Mats

But I used cin.get(person1.name,50,'\n') so why won't it work? If cin.get is significantly different from getline could you tell me how I could use getline to replace cin.get in the code i posted earlier?

getline and get behave the same way. You can only get the infinite loop of bad input you appear to be talking about if you try to read numeric input directly. You can't get an infinite loop on inputting a string or characters.

I'm using cin.get to get a string aren't I? So why does it still error?

Quote:

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Originally Posted by KgNe

I'm using cin.get to get a string aren't I? So why does it still error?

---

I assume the error is on the very next line after the bit you posted where it says cin >> person1.age. I will continue to believe that until you convince me otherwise. (In other words: I have been completely unable to make the snippet you posted behave in any violent manner.)

Ok I fixed it. It occured to me that since I'm using a character array, it would error if the user didn't cin a character, which apparently was what a certain something in the buffer or something although I supposedly cleared the buffer, but once I used string and getline, it worked. Anyway does anyone know what is classing exactly?

Quote:

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Originally Posted by KgNe

Anyway does anyone know what is classing exactly?

---

Not sure. In what context does it occur?

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Mats

Like I have to use it to make my code for this project look neater or something

Quote:

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Originally Posted by KgNe

Like I have to use it to make my code for this project look neater or something

---

Is this in English, or are you translating from something else. I can't see the word on this page [other than in your post and my quote of your post]. Google does have some results for classing, but they appear to relate to wool or cotton, and I don't think producing good quality cloth is much related with good quality code [other than "lint" being loose fibers on cloth, and a tool that detect potential bugs in C code].

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Mats

Hmm apparently it's just using classes in my program to handle functions. How should I go about doing that? Why is there a need to use classes to handle my functions?

There is no application that NEEDS to be solved with classes. There are three reasons to use classes:
1. The boss/teacher says so. [this is the most important one if you want to succeed in a job/course].
2. The problem becomes easier to solve by using classes.
3. Someone else says so. This is the poorest of all reasons.

Almost all programs that exist today have been written in plain C - if you want to use C++, then you have the possibility to use classes, and they can often help make a problem easier to solve. But there is no "must" in this.

Without you describing what the actual goal of the project is, it would be impossible for me to advice whether this is a project where classes are beneficial [of course, there are some people who would say that all programs are best written using classes, and when it comes to LARGE systems, object oriented techniques will definitely be beneficial - even if the language is not C++ - other than that, it becomes a question of belief and principles rather than "must/can't"].

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Mats

Ok this project is to make a simple text-based game, of course we have experienced people who are going crazy with the project, people doing way over their limits, people doing what they can, etc etc. So currently, what interests me about your post is the 2nd reason, and it would be nice if you could show me a very simple example on how classes can do that.

Quote:

---

Originally Posted by KgNe

Ok this project is to make a simple text-based game, of course we have experienced people who are going crazy with the project, people doing way over their limits, people doing what they can, etc etc. So currently, what interests me about your post is the 2nd reason, and it would be nice if you could show me a very simple example on how classes can do that.

---

This is, I presume, a school project?

As to how you classes help, that's an awfully large subject.

One aspect may be that you want to have different objects that the player can carry around, and possibly use as weapons.

So you may start with a basic object:

Code:

---

class baseobject
{
private:
  string shortDesc;
  string longDesc;
public:
  baseobject(const string &sdesc,  const string &ldesc);
  virtual void Describe(bool brief);
  virtual bool isWeapon() { return false; }
};

class weapon: public baseobject
{
  weapon(const string &sdesc,  const string &ldesc, float damageValue);
  bool isWeapon() { return true; }
  void useWeaponOn(...);
};

---

This can be expanded quite a bit, but it shows the basic principle.

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Mats

Lemme see if I got the code correctly.

The class baseobject is like a class for all the types of items that the player can carry in his/her inventory. virtual void Describe would have the description of the item. virtual bool isWeapon() determines if the item is a weapon and is false by default.

The class weapon is like a class for the weapon type of item. isWeapon() would be true because it is a weapon.

Parts I don't get :
What is shortDesc and longDesc supposed to mean?
useWeaponOn means equip or don't equip? or does it mean something else?
No idea whats a virtual data type yet =(

Quote:

---

Originally Posted by KgNe

Lemme see if I got the code correctly.

The class baseobject is like a class for all the types of items that the player can carry in his/her inventory. virtual void Describe would have the description of the item. virtual bool isWeapon() determines if the item is a weapon and is false by default.

The class weapon is like a class for the weapon type of item. isWeapon() would be true because it is a weapon.

---

Yup, that's pretty much it. Although, my thoughts was that baseobject::Describe would do something like this, which hopefully answers your question below as well:

Code:

---

void baseobject::Describe(bool brief)
{
  if (brief) cout << shortDesc;
  else cout << longDesc << endl;
}

---

Quote:

---

Parts I don't get :
What is shortDesc and longDesc supposed to mean?
useWeaponOn means equip or don't equip? or does it mean something else?
No idea whats a virtual data type yet =(

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Let's start with virtual - it essentialy means "use the object itself to find the function". Without virtual, the compiler uses the object-type of the current variable to find the function. With virtual, the object holds a pointer to the function [usually in the form of a vtable to be precise]. The purpose of this is that we can then use a baseobject pointer to hold an object [e.g. a vector of baseobject pointers], but the list could hold weapons and other derived objects that have different properties.

So, for example:

Code:

---

vector<baseobject> stuff;
baseobject *pillow = new baseobject("pillow", "A soft pillow - it looks so comfortable that you may want to rest your head on it right now");
weapon *axe = new weapon("axe", "A very sharp looking axe", 0.5);

stuff.push_back(pillow);
stuff.push_back(axe);

...
for(int i = 0; i < stuff.Size(); i++)
{
  if (stuff[i]->isWeapon()) {
      cout << "You can use ";
      stuff[i]->Describe(true);
      cout << "as a weapon";
  }
}

---

For the above to work, we obviously need isWeapon to be called on the weapon class for axe to be recognized as a weapon.

My idea of "useWeaponOn" was more like when you say "Fight monster with axe", it would do "axe->useWeaponOn(monster)".

I think the description stuff is clarified by the examples.

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Mats

Ahh OK I can roughly get it. Read up on the whole Cprogramming.com tutorial before continuing would be a good idea?