Evaluate an expression with a specific layer as the active layer.
BOOL LT_evaluate( LPCSTR lpcszLabTalkExpression, double * lpdbResult )
TRUE if expression is valid, FALSE if expression leads to missing value
//Check if the labtalk expression is right.
GraphLayer gl = gp.Layers(0);
bRet = gl.LT_evaluate("layer.height", &vv);
out_str("The labtalk expression is valid");
out_str("The labtalk expression is not valid");
The Layer Object is only temporarily set as the active layer. The Layer that was active before the code executes is restored as active upon return.