Page 81 - DCAP408_WEB_PROGRAMMING

Unit 4: Windows Controls

4.9 Edit Controls Notes

One of the most generally used controls in the windows environment, the EDIT control, is used
to permit the user to enter, modify, copy, etc... text. Windows Notepad is little more than a plain
old window with a big edit control inside it.

Example: Here is the code used to interface with the edit control in this example:
SetDlgItemText(hwnd, IDC_TEXT, “This is a string”);

That’s all it takes to modify the text included in the control (this can be used for pretty much any
control that has a text value connected with it, STATICs, BUTTONs and so on).
Retrieving the text from the control is simple as well, though a little more work than setting it...
int len = GetWindowTextLength(GetDlgItem(hwnd, IDC_TEXT));
if(len > 0)
{
int i;
char* buf;

buf = (char*)GlobalAlloc(GPTR, len + 1);
GetDlgItemText(hwnd, IDC_TEXT, buf, len + 1);

//... do stuff with text ...

GlobalFree((HANDLE)buf);
}
Initially, we need to assign some memory to store the string in, it won’t just return us a pointer
to the string previously in memory. So as to do this, we first require to know how much
memory to assign. There isn’t a GetDlgItemTextLength(), but there is a GetWindowTextLength(),
so all we require to do is obtain the handle to the control by means of GetDlgItem().
Now that we have the length, we can assign some memory. Here I’ve added a verify to observe
if there is any text to start with, as most likely you don’t want to be working with an empty
string... at times you might, but that’s up to you. Presuming that there is something there to
function with, we call GlobalAlloc() to assign some memory. GlobalAlloc() as I’ve used it here
is equivalent to calloc(), if you’re used to DOS/UNIX coding. It assigns some memory, initializes
it’s contents to 0 and returns a pointer to that memory. There are dissimilar flags you can pass as
the first parameter to make it behave differently for different purposes, but this is the only
manner we will be using it.

Notes Observe that we added 1 to the length in two positions, what’s up with that? Well,
GetWindowTextLength() returns the number of characters of text the control includes
NOT INCLUDING the null terminator. This signifies that if we were to assign a string
Contd...

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