asked on

Help using pointers? access violation

Hi,

i'm probably doing something extremely basic wrong but i'm having problems with pointers.

i have a method

Code:

BUTTON* getButton(int i, int j){ return hookFile.hooks[i]->buttons[j]; }

this returns a button ctruscture i have created. Now the hook[i] has been created i know this but the button hasn't when i get this message. i have tried

Code:

BUTTON* rBut = getButton(i,j);
if(rBut == NULL)
break;

to stop it running to the code causing the error, however this isn't working when i add my hook i set all the buttons to be NULL. but if i put a break point here rBut equals 409e62.

Code:

void addHook(LPTSTR window)
{
      int i;
      for(i=0; i<maxHooks; i++)
            if(hookFile.hooks[i] == NULL)
                  break;

      if(i < maxHooks)
      {
            HOOK nHook;

            HGLOBAL memPtr = GlobalAlloc(GMEM_FIXED, strlen(window)+1); //pointer to mem block

            if( memPtr && (nHook.window = (LPTSTR)GlobalLock(memPtr)) != NULL )
                  RtlMoveMemory(nHook.window, window, strlen(window)+1);
            else
            {
                  char buf[128];
                  sprintf(buf, "Error Unable to allocate Memory for hook file hook:window.");
                  MessageBox(NULL, buf, NULL, 0);
            }

            hookFile.hooks[i] = &nHook;

            int j; //make all NULL
            for(j=0; j<maxButtons; j++)
                  hookFile.hooks[i]->buttons[j] = NULL;
      }
}

Now the structures and add methods i keep in a struct.cpp the method which i read the structure and display it is held in a dialog.cpp. I have noticed that the hooks[i]->window is also returning something which isn't correct.

what am i doing wrong please?

many thanks,

Matt.

Infinity08

Has the buttons array within the HOOK struct hookFile.hooks[i] been allocated ?

At which line does the code crash ?

SOLUTION

jasonclarke

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flynny

ASKER

hi thanks for the replies the code crashes when i try to insert into a CTreeCtrl, in which i display the structure.

the program crashes when trying to access a variable of the structure, i assumed this is because i it didn't exist although it was returning something. this was why i was testing to see if it was null.

i think jason is on the right lines here. is there anyway i can make the whole structure globally available?

matt.

ASKER CERTIFIED SOLUTION

Infinity08

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Infinity08

Don't forget to free the memory again once you don't need it any more !!! Otherwise you'll have a memory leak.

flynny

ASKER

brilliant thank you so much for your help

flynny

ASKER

ok so to free the memory all i have to do is free(pHook) for example? i've always had problems with the free function.

jasonclarke

To free all of the memory you would do something like this:

for(i=0; i<maxHooks; i++)
{
if(hookFile.hooks[i] == NULL)
break;
GlobalFree(hookFile.hooks[i] ->window);
GlobalFree(hookFile.hooks[i]);
hookFile.hooks[i] = NULL;
}