A.M. Hoornweg

I did consult the wiki but somehow managed to skip this line of text ten times. It must be monday morning .... Thanks for pointing it out!

Hello all, is there a way to quickly initialize all local variables of a procedure with zero, maybe using FillChar? It would be very practical to use at the beginning of a procedure. I had a case recently where the Delphi compiler didn't throw a warning when I accessed a local variable before it had been initialized and it had me debugging for hours.

Generally, yes. But it would also be great to have a nifty tool at my disposal that lets me wipe all locals on the stack with a single call, especially if it is a complex routine with lots and lots of local vars. In such cases it would simply save a lot of boilerplate code. Delphi does the very same thing for class members and I would totally hate it if it didn't. I had hoped that this would be a trivial thing to write, since all StdCall procedures start with a byte sequence like "mov ebp,esp; add esp, -sizeof(localvars)".

Normally yes. I only asked because I overlooked initializing a certain local variable and the compiler (Delphi XE, which is used in that specific project) didn't warn me. OTOH, if Delphi takes the trouble to zero-fill managed local variables anyway, it puzzles me why it does not simply fill the rest as well. A REP STOSD is lightning fast.

It seems to vary with compiler versions. I use both XE and Sydney.

Can you use the postal code to identify the town and street? In the Netherlands we have a system where the postal code combined with the house nr uniquely identifies an address. For example, enter "Netherlands 2594 BD 10" in google Maps and you'll see where our king lives.

The reason is, that when S goes out of scope, it decrements the reference count of G. G should only be destroyed when its reference count reaches zero so that action must be atomic.

That may very well be true. But when a developer is doing refactoring to make code more legible and concise, IMHO it is a good thing if the parameter list reflects the intended use of the parameters. So if a parameter is intended just for outputting something and not for modifying an existing value, the "out" modifier is clearer than "var". I find "const" parameters confusing at times, especially when passing stuff like arrays. If I pass an array as a const, am I supposed to be able to modify elements or not? The Delphi documentation (link at he bottom) says "... constant parameters are similar to value parameters, except that you cannot assign a value to a constant parameter within the body of a procedure or function..." . I don't want to nit-pick, but I find it very confusing and counter-intuitive that I can modify the array in such a case. Type tintarray=tarray<integer>; Procedure dosomething (CONST a:tintarray); var i:integer; begin for i:=0 to high(a)-1 do a[i]:=random(maxint); end; procedure TForm1.Button1Click(Sender: TObject); var x:tintarray; begin setlength(x,10); //newly allocated space is set to 0 dosomething(x); showmessage(format('%d',[x[0]])); end; http://docwiki.embarcadero.com/RADStudio/Sydney/en/Parameters_(Delphi)#Constant_Parameters

Unlike "shortstring", Delphi cannot pass managed types such as strings by value. It is always a pointer. I'm not 100% sure but I think an "out" parameter is like a "promise" to return a value no matter what, and also a promise not to use it for input. The problem being that it is possible to pass the same variable twice and thus circumvent the no-input promise.

"Out" parameters of managed types (such as strings, interfaces, dynamic arrays) are initialized before a method is called. The problem only arises because multiple parameters in the method reference the same string. The behavior is correct but very counter-intuitive. It would behave more intuitively if the compiler would issue a UniqueString() for the second/identical parameter.

I posted about it before in this forum and was told that it's intended behavior. Admittedly, it's a corner case, but it did happen and cost me a lot of time to figure it out. A compiler warning would have been nice.

There's also this thingy called "tGridpanel" in Delphi. I have never used it myself though.

How about metadata (access rights) , triggers etc?

"Out" parameters are an even bigger can of worms. I had refactored some code recently to use "OUT" parameters instead of VAR parameters (in order to more clearly document the intended use) and it had side effects that were hard to figure out. I thought my debugger had gone bananas. Try single-stepping through this code and watch the values. In hindsight, the cause is clear, but I find the compiler should throw a warning if it encounters such a situation. I now avoid OUT parameters. procedure tform2.test(OUT somestring:String; Defaultvalue:String); begin Somestring:=Defaultvalue; end; procedure TForm2.Button1Click(Sender: TObject); var t:string; begin t:='Testing 1-2-3'; Test(t,t); Showmessage(t); end;

TMS FixInsight (a sourcecode analysis tool) flags non-const string parameters as bad practice if these strings are never written to.

Did you install any software or packages recently that changed your system's "path" variable? The Windows PATH variable has a limited maximum length. If setup routines keep adding entries to it then it may get truncated and all sorts of things on your system stop working properly. Like Delphi not finding its installed BPL's anymore. Happens to me all the time. Some component manufacturers (like TMS) store BPL's in non-standard locations and that regularly causes me headaches for this reason. I really wish component manufacturers would stop doing that.

My current approach is to store all *.PNG files in high resolution inside the resources. I scale them down to the appropriate size when the application starts and the display resolution is known. I use my own scaling routines (using a Lanczos2 filter) but there are lots of libraries that can do the same thing. This approach does not solve the situation of the user having multiple screens in multiple resolutions though.

@emailx45 you're kinda missing the point. Decoding is not the issue here. My point is that a "month" does not have a constant value. So expressing a countdown as "2 months and 5 days left until..." is totally vague. If there is a distance of 29 days between two dates, that distance can be either exactly one month, one month plus a day, one month minus a day or one month minus two days, depending on where in the calendar you are.

There are several pitfalls here. The most important one: months don't have a constant length. For example, assume it is February 14. How many months and days is it until March 13? And until March 15?

Somehow I totally missed this, but in october 2017 Microsoft did a complete U-turn on deprecating OleDB database connectivity. They have even released new OleDB providers for MS Sql Server which will be maintained and updated with the most recent server features. https://blogs.msdn.microsoft.com/sqlnativeclient/2017/10/06/announcing-the-new-release-of-ole-db-driver-for-sql-server/ https://docs.microsoft.com/en-us/sql/connect/oledb/oledb-driver-for-sql-server?view=sql-server-2017

I mean a tool to analyze large existing projects with many units. Maybe something like TMS Fixinsight Pro.

Especially tricky to optimize are hidden managed variables. Delphi creates those when it needs to store intermediate results of managed types [as in tstringlist.add (format('Test %d',[123]))]. It would be great if there were developer tools that would point out the creation of such hidden variables.

Fair enough. You're using the stringlist as an internally shared object, just for saving some time by not having to create/destroy one whenever you need one. You could take that concept one step further by creating a global stringlist pool (a singleton) from which you can request an available tStringlist whenever you need one. That pool could be shared among many objects and you could even make it threadsafe if you want. The problem of having local variables of managed data types such as strings is that Delphi needs to guarantee that no memory leaks occur. So there's always a hidden Try/Finally block in such methods that will "finalize" the managed variables and release any allocated heap space. That takes time to execute, even if there's no further "code" in the method.

All the time. I am especially fond of classes that have only class methods. They basically act as namespaces.

What exactly is a "local field" ? Do you mean a private field of a class (a member of an instantiated object, located on the heap) , or do you mean a local variable of a procedure or method (located on the stack) ?