Finding out if a variable exists

#1 I don't know the answer to this one but this may help (albeit in a different way).

The engine code "console\compiledEval.cc" (Line 319)

Uncomment the lines ...

//if(!currentVariable)
//Con::warnf(ConsoleLogEntry::Script, "Variable referenced before assignment: %s, name);

... and recompile. If it's not there then add the code as the last lines in the function "ExprEvalState::setCurVarName(...)".

This at least will tell you at runtime whether you are attempting to reference a variable before assignment.

Hope this helps.

#2 No there isn't but I believe

if(%a > 0)
  bla();

works.

I believe, I can't remember correctly, that if you have a variable that is not assigned anything that it just contains 0.

So either a boolean check or an > 0 check will work.

#3 But what if the variable you wanted to see if it existed actually did and was purposely set to zero at the time.

#4 Like I said I'm not sure. But variables with % are local to a function anyway, so really it is the programmers responsibility to make sure he doesnt declare 2 variables with the same name in that function -- which is impossible with the script anyway.

example:

function foo()
{
   %a = true;
   if(%a)
      bla();
   else
      bla2();

   %a = "Torque Gaming System"; // oops

   if(%a)
      bla();
}

In this exampe it is the programmers responsibility to be aware of what variables he is using for what types of data because the script is not strongly typed -- meaning a variable can contain pretty much any data you want to give it.


Now check out the code below. This is really the only way I can have two variables with relatively the same name, but even then I must supercede the one with %this. a since it is part of the script object.

if(!isObject(Example))
{
   new ScriptObject(Example) 
   {
      class = FilterHud;
      a = false;
   };
}
function Example::bla(%this)
{
   %a = "Hello world!";
   %this.a = true;

   // prints "Hello world!" to console
   echo(%a);

   // prints true to console
   echo(%this.a);
}
function Example::bla2(%this)
{
   // prints nothing to the console
   echo(%a);

   // prints true to the console
   echo(%this.a);

   %this.a = false;
}

#5 I used locals becuase it was an easy example. Globals are the problem. And passed locals are just as much of a menace.

#6 Undefined variables are the empty string when evaluated in a string context. So just check for $= "" unless you might intentionally be setting variables to the empty string.

#7 I don't know about using the existing namespace, but using the global namespace, you can implement the following function in C++. As usual, my examples are in MyExtensions.cc, but you can put them where appropriate.


======== MyExtensions.cc ============
#include "platform/platform.h"
#include "console/console.h"
#include "console/consoleInternal.h"
#include "console/ast.h"
#include

#ifdef LOG_INPUT
#include
#include
#endif

ConsoleFunction(globalVariableExists, bool, 2, 2, "globalVariableExists(variableName)")
{
argc;

StringTableEntry name = StringTable->lookup(argv[1]);

return gEvalState.globalVars.lookup(name);
}
=========================

Now, in the console window (or in a script) you can enter:

echo(globalVariableExists("$Test"));

the result is 0.

$Test="My test";
echo(globalVariableExists("$Test"));

the result is 1.

Does that help any?

#8 Good thinking Tony!