by Fenton Webb
Issue
I have a command line that is asking the user for a password. In this situation I need to display a * for each entered character by the user. How is it possible to do it?
Solution
It would not help to use acedGetString, as it always echoes the characters as they are typed. If you don’t want to use a dialog, you can create your own function in ObjectARX to prompt the user for a password in AutoCAD, yet have the console show only "*" for each character typed, much like password entry in Windows.
The basic idea is to set a Windows Hook which can monitor any keyboard input to a normal call to acedGetString() before AutoCAD gets it. From there you can record what has been typed in your own buffer, and replace the keystroke with a generic "*". When the function is done, you can return your buffer instead of what AutoCAD has actually received (i.e. a string of "****"s).
This example creates the function adskGetPassword() which has the identical signature and return type as acedGetString(), and it can be used interchangeably, however any typed input will appear as ‘*’ in adskGetPassword(). For questions about the arguments, have a look at the ObjectARX online help under acedGetString() for details.
As far as security is concerned, the routine is safe to use except if any applications have set hooks in the chain before this one, or if any application has sub classed the AutoCAD frame window. These applications may be able to monitor the keystrokes before our function is able to change them. If more security is desired, take a look at the Password Dialog available from Microsoft.
Here is the code:
ACHAR*pResult; // a global pointer to the result…
int resultLen; // a global lengh
int crTerminated;// a global flag for cronly
int adskGetPassword(int cronly,ACHAR* prompt,ACHAR* result)
{
ACHAR tempResult[256];
pResult=result;// set our global pointer…
resultLen=0;// and reset our length.
int resultVal;// this is what acedGetString returns (ie escape etc)
crTerminated=cronly;// set our global flag for cronly
acedRegisterFilterWinMsg(MessageFilter);// Set the Hook.
resultVal=acedGetString(cronly,prompt,tempResult);// Call GetString…
acedRemoveFil
terWinMsg(MessageFilter);// Remove the Hook.
result[resultLen]=‘\0’;// Null terminate the result
return resultVal;
}
// Here is the callback…it will be called for many types of messages sent to AutoCAD.
BOOL MessageFilter(MSG *pMsg)
{
if(pMsg->message==WM_CHAR)// a char has been typed…
{
int keyCode=pMsg->wParam;
if(keyCode!=8 && keyCode!=13 && keyCode!=27 && ((keyCode!=32)||crTerminated))
{
// keyCode 8 is Backspace
// Keycode 27 is Escape
// Keycode 32 is Space (only avoided if cronly is used)
pMsg->wParam=42;// For Security against subsequent hooks, and display,
pMsg->lParam=589825;// Set these two to reflect ‘*’ keystroke
pResult[resultLen]=keyCode;// but keep the real keycode.
resultLen++;
}
if(keyCode==8 && resultLen)
resultLen–;
}
return FALSE;
}
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