Mega Code Archive
Understanding pointers for the amateurs
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Title: Understanding pointers for the amateurs
Question: This article is just for them who dont have any idea of what a pointer is, and does only describe it in the simple way.
Answer:
Understanding pointers for the amateurs
Written for all the beginners out there
This article is just for them who dont have any idea of what a pointer is, and does only describe it in the simple way.
A pointer is like a web-address, it points to something: a record, an integer, a string, (...).
Many API functions have pointers as arguments, like the ShellExecuteEx function. It's delclared like this in the MAPI help file:
ShellExecuteEx(
LPSHELLEXECUTEINFO lpExecInfo // pointer to SHELLEXECUTEINFO structure
);
To manage this, you find out what this structure if built up of:
typedef struct _SHELLEXECUTEINFO { // sei
DWORD cbSize;
ULONG fMask;
HWND hwnd;
LPCSTR lpVerb;
LPCSTR lpFile;
LPCSTR lpParameters;
LPCSTR lpDirectory;
int nShow;
HINSTANCE hInstApp;
// Optional members
LPVOID lpIDList;
LPCSTR lpClass;
HKEY hkeyClass;
DWORD dwHotKey;
HANDLE hIcon;
HANDLE hProcess;
} SHELLEXECUTEINFO, FAR *LPSHELLEXECUTEINFO;
Then, you assign values to the fields in a variable of this structure, and simly writes this:
ShellExecuteEx(@MyShellExecuteInfo);
An example from the internet: Instead of sending the great Delphi-page you found yesterday to a friend, you just send the web-address, so he can find it at the same place. Thats the principle of pointers. Not much, is it?
When you use pointers, you use two operators to tell what you mean: @ and ^. See the example under to see how.
If you who read this now CAN this, please write a comment, and explain more. I dont know much more than Ive just written!
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A short pointer example:
(To test this, choose File|New|Other|Console Application)
program UsePointer;
{$APPTYPE CONSOLE}
type
MyPInteger = ^Integer; // This means: MyPInteger is a pointer type to a Integer
var
X: Integer;
procedure PrintOutInt(P: MyPInteger);
begin
WriteLn(P^); // Find the information at the address of P
ReadLn; //Just to hang the program
end;
begin
X := 17;
PrintOutInt(@X); // Send the address of X as a parameter.
end.
Write P1 := P2 if you want to assign the memory address to another pointer.
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About this article and me: Im still a beginner with Delphi and I want to teach those who are at the same level as me what I know.
All the articles Ive written till now is at the same level, and (I really hope!) easy to understand. Feel free to take a look at them too, and of course: I also want contact with Delphi programmers at my level (and age: 15). Hint, hint
Martin Strand marstr2@online.no (.no means Norway. I understand Norwegian, Swedish, Danish, English and some German.)
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