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spinaltap 11Jun2007 22:51

Simple C++ problem
 
Hello.I'm a complete beginner with C++.I've been using the Devbloodshed IDE and running it on Windows XP.
All I've really run is simple apps with loops and arrrays etc.Anyway,I really want to learn how to
create windows applications.This may sound like a simple error to some:
int *buf = GlobalAlloc(GPTR, sizeof(int) * count);
I recieve an invalid convert from void to int error at this line.
I've tried doing a simple cast such as
int *buf =(int) GlobalAlloc(GPTR, sizeof(int) * count);
and tried using dynamic and static casts all to no avail.
What is interesting is this, GlobalAlloc function doesn't have a return,so how can it return anything other than void anyway?
This isn't my application.The exe runs fine,but not when I try to run it in the Ide.
Any help appreciated.I've listed the 1 compilation error in the code with a
//my error comment.
Code:


#include <windows.h>
#include "resource.h"
BOOL CALLBACK DlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
 switch(Message)
 {
  case WM_INITDIALOG:
  // This is where we set up the dialog box, and initialise any default values
  SetDlgItemText(hwnd, IDC_TEXT, "This is a string");
  SetDlgItemInt(hwnd, IDC_NUMBER, 5, FALSE);
  break;
  case WM_COMMAND:
  switch(LOWORD(wParam))
  {
    case IDC_ADD:
    {
    // When somebody clicks the Add button, first we get the number of
    // they entered
    BOOL bSuccess;
    int nTimes = GetDlgItemInt(hwnd, IDC_NUMBER, &bSuccess, FALSE);
    if(bSuccess)
    {
      // Then we get the string they entered
      // First we need to find out how long it is so that we can
      // allocate some memory
      int len = GetWindowTextLength(GetDlgItem(hwnd, IDC_TEXT));
      if(len > 0)
      {
      // Now we allocate, and get the string into our buffer
      int i;
      char* buf;
      buf = (char*)GlobalAlloc(GPTR, len + 1);
      GetDlgItemText(hwnd, IDC_TEXT, buf, len + 1);
      // Now we add the string to the list box however many times
      // the user asked us to.
      for(i = 0;i < nTimes; i++)
      {
        int index = SendDlgItemMessage(hwnd, IDC_LIST, LB_ADDSTRING, 0, (LPARAM)buf);
        // Here we are associating the value nTimes with the item
        // just for the heck of it, we'll use it to display later.
        // Normally you would put some more useful data here, such
        // as a pointer.
        SendDlgItemMessage(hwnd, IDC_LIST, LB_SETITEMDATA, (WPARAM)index, (LPARAM)nTimes);
      }
      // Dont' forget to free the memory!
      GlobalFree((HANDLE)buf);
      }
      else
      {
      MessageBox(hwnd, "You didn't enter anything!", "Warning", MB_OK);
      }
    }
    else
    {
      MessageBox(hwnd, "Couldn't translate that number :(", "Warning", MB_OK);
    }
    }
    break;
    case IDC_REMOVE:
    {
    // When the user clicks the Remove button, we first get the number
    // of selected items
    HWND hList = GetDlgItem(hwnd, IDC_LIST);
    int count = SendMessage(hList, LB_GETSELCOUNT, 0, 0);
    if(count != LB_ERR)
    {
      if(count != 0)
      {
      // And then allocate room to store the list of selected items.
      int i;
 //my error  int *buf = GlobalAlloc(GPTR, sizeof(int) * count);
      SendMessage(hList, LB_GETSELITEMS, (WPARAM)count, (LPARAM)buf);
     
      // Now we loop through the list and remove each item that was
      // selected. 
      // WARNING!!! 
      // We loop backwards, because if we removed items
      // from top to bottom, it would change the indexes of the other
      // items!!!
      for(i = count - 1; i >= 0; i--)
      {
        SendMessage(hList, LB_DELETESTRING, (WPARAM)buf[i], 0);
      }
      GlobalFree(buf);
      }
      else
      {
      MessageBox(hwnd, "No items selected.", "Warning", MB_OK);
      }
    }
    else
    {
      MessageBox(hwnd, "Error counting items :(", "Warning", MB_OK);
    }
    }
    break;
    case IDC_CLEAR:
    SendDlgItemMessage(hwnd, IDC_LIST, LB_RESETCONTENT, 0, 0);
    break;
    case IDC_LIST:
    switch(HIWORD(wParam))
    {
      case LBN_SELCHANGE:
      {
      // Get the number of items selected.
      HWND hList = GetDlgItem(hwnd, IDC_LIST);
      int count = SendMessage(hList, LB_GETSELCOUNT, 0, 0);
      if(count != LB_ERR)
      {
        // We only want to continue if one and only one item is
        // selected.
        if(count == 1)
        {
        // Since we know ahead of time we're only getting one
        // index, there's no need to allocate an array.
        int index;
        int err = SendMessage(hList, LB_GETSELITEMS, (WPARAM)1, (LPARAM)&index);
        if(err != LB_ERR)
        {
          // Get the data we associated with the item above
          // (the number of times it was added)
          int data = SendMessage(hList, LB_GETITEMDATA, (WPARAM)index, 0);
          SetDlgItemInt(hwnd, IDC_SHOWCOUNT, data, FALSE);
        }
        else
        {
          MessageBox(hwnd, "Error getting selected item :(", "Warning", MB_OK);
        }
        }
        else
        {
        // No items selected, or more than one
        // Either way, we aren't going to process this.
        SetDlgItemText(hwnd, IDC_SHOWCOUNT, "-");
        }
      }
      else
      {
        MessageBox(hwnd, "Error counting items :(", "Warning", MB_OK);
      }
      }
      break;
    }
    break;
  }
  break;
  case WM_CLOSE:
  EndDialog(hwnd, 0);
  break;
  default:
  return FALSE;
 }
 return TRUE;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
 LPSTR lpCmdLine, int nCmdShow)
{
 return DialogBox(hInstance, MAKEINTRESOURCE(IDD_MAIN), NULL, DlgProc);
}


DaWei 12Jun2007 01:52

Re: Simple C++ problem
 
Why do you say it doesn't have a return? What makes you think that? It returns a handle to the allocated memory, or NULL if it fails. You're trying to cast its return to an int and assign that to an int *. You can't assign an int to an int * anywhere, not just this call.


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