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    <p>Yes you can do that, using the <a href="http://msdn.microsoft.com/en-us/library/ms680553%28VS.85%29.aspx" rel="noreferrer"><code>ReadProcessMemory</code></a> and <a href="http://msdn.microsoft.com/en-us/library/ms681674%28VS.85%29.aspx" rel="noreferrer"><code>WriteProcessMemory</code></a> functions to patch the code of the current process. Basically, you get the address of the procedure or function to patch and then insert a Jump instruction to the address of the new procedure.</p> <p>Check this code</p> <pre><code>Uses uThirdParty; //this is the unit where the original DataCompare function is declarated type //strctures to hold the address and instructions to patch TJumpOfs = Integer; PPointer = ^Pointer; PXRedirCode = ^TXRedirCode; TXRedirCode = packed record Jump: Byte; Offset: TJumpOfs; end; PAbsoluteIndirectJmp = ^TAbsoluteIndirectJmp; TAbsoluteIndirectJmp = packed record OpCode: Word; Addr: PPointer; end; var DataCompareBackup: TXRedirCode; //Store the original address of the function to patch //this is the implementation of the new function function DataCompareHack(const S1, S2: string; APartial: Boolean): Boolean; begin //here write your own code end; //get the address of a procedure or method of a function function GetActualAddr(Proc: Pointer): Pointer; begin if Proc &lt;&gt; nil then begin if (Win32Platform = VER_PLATFORM_WIN32_NT) and (PAbsoluteIndirectJmp(Proc).OpCode = $25FF) then Result := PAbsoluteIndirectJmp(Proc).Addr^ else Result := Proc; end else Result := nil; end; //patch the original function or procedure procedure HookProc(Proc, Dest: Pointer; var BackupCode: TXRedirCode); var n: {$IFDEF VER230}NativeUInt{$ELSE}DWORD{$ENDIF}; Code: TXRedirCode; begin Proc := GetActualAddr(Proc); Assert(Proc &lt;&gt; nil); //store the address of the original procedure to patch if ReadProcessMemory(GetCurrentProcess, Proc, @BackupCode, SizeOf(BackupCode), n) then begin Code.Jump := $E9; Code.Offset := PAnsiChar(Dest) - PAnsiChar(Proc) - SizeOf(Code); //replace the target procedure address with the new one. WriteProcessMemory(GetCurrentProcess, Proc, @Code, SizeOf(Code), n); end; end; //restore the original address of the hooked function or procedure procedure UnhookProc(Proc: Pointer; var BackupCode: TXRedirCode); var n: {$IFDEF VER230}NativeUInt{$ELSE}Cardinal{$ENDIF}; begin if (BackupCode.Jump &lt;&gt; 0) and (Proc &lt;&gt; nil) then begin Proc := GetActualAddr(Proc); Assert(Proc &lt;&gt; nil); WriteProcessMemory(GetCurrentProcess, Proc, @BackupCode, SizeOf(BackupCode), n); BackupCode.Jump := 0; end; end; //Patch the original procedure or function procedure HookDataCompare; begin //look how is passed the address of the original procedure (including the unit name) HookProc(@uThirdParty.DataCompare, @DataCompareHack, DataCompareBackup); end; //restore the address of the original procedure or function procedure UnHookDataCompare; begin UnhookProc(@uThirdParty.DataCompare, DataCompareBackup); end; initialization HookDataCompare; finalization UnHookDataCompare; end. </code></pre> <p>Now every time you execute your app and a call to the <code>DataCompare</code> function was made, the jump instruction (to he new address) will be executed causing which the <code>DataCompareHack</code> function will be called instead.</p>
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    1. POHow to change the implementation (detour) of an externally declared function
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    1. PTAnswer
    1. USLieven Keersmaekers
    1. USRRUZ
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    1. POHow to change the implementation (detour) of an externally declared function
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    1. VO
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      1. VTUpMod
    2. VO
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      1. This table or related slice is empty.
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    1. CONow where did you learn that? That's way to cool to be called a hack. Instead of calling it a "Hack" I think you should call it a "Ninja". DataCompareNinja
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      1. USMichael Riley - AKA Gunny
    2. CO+1 for you, @RRUZ. Excellent answer.
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      1. USAriel Rivas
    3. COThis kind of redirection is known as a Detour. Microsoft has a research project about it: http://research.microsoft.com/en-us/projects/detours/
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      1. USRemy Lebeau
 

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