Re: [fpc-pascal] Function to create a record ?
Travis Siegel via fpc-pascal said on Sun, 4 Jun 2023 19:38:44 + > >On 6/4/2023 1:37 PM, Steve Litt via fpc-pascal wrote: >> Henry Vermaak via fpc-pascal said on Fri, 2 Jun 2023 09:38:17 +0100 >> >>> On Fri, 2 Jun 2023 at 01:36, Steve Litt via fpc-pascal >>> wrote: fillchar(junkvar, junkvar_size, 'b'); person := modperson(person, 'Martin'); person := modperson(person2, 'Maria'); >>> Maybe a typo? (E.g. person2 := modperson(person2, 'Maria')) >>> >>> Henry >> Thanks Henry! >> >> You're right: Changing the second person := to person2 := did just >> what I wanted it to do. >> >> Because returning a local array or string as a function return in C >> leads to horrible intermittents due to the local going out of scope >> and relinquishing the local's stack, which can then be overwritten, >> I added a procedure, a function, and a main program statement which >> each consumed two million bytes of local variables, and the person >> and person2 didn't get overwritten. Very cool. >> >> When I increased the huge local vars to three million bytes, the >> program segfaulted. I figure I just ran it out of stack, but until I >> did, the huge local vars didn't trash the contents of person and >> person2. >> >> Thanks for your help. >> >> SteveT >Depending on the compiler *not* to overwrite local variables is most >certainly the wrong way to go with this. You really should create >either a global record/object, or use functions to pass around the >information you need. Expecting the operating system to keep local >variables after the area goes out of scope is just begging for errors >later on when the compiler/os treatment of said areas changes. Thanks Travis, This is the info I was asking for. Yeah, passing the local as a function return worked, but because of a horrible experience doing that in C, I was suspicious and leery of actually using that technique. I'll just use new and dispose. Thanks, SteveT Steve Litt Autumn 2022 featured book: Thriving in Tough Times http://www.troubleshooters.com/bookstore/thrive.htm ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Choice of exceptions to use?
On Sun, Jun 4, 2023 at 11:58 AM Graeme Geldenhuys via fpc-pascal wrote: > Initially I was leaning towards the Range exception, but now I'm > thinking that maybe the Argument exception is more appropriate > (based on the descriptions seen in the linked docs). I would go for range exception, since the offending coordinates are out of range. Invalid Argument for me would apply to situations like a wrong type for a format specifier. -- Bart ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
OK, I understand mostly. Thanks. Juha ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Function to create a record ?
Depending on the compiler *not* to overwrite local variables is most certainly the wrong way to go with this. You really should create either a global record/object, or use functions to pass around the information you need. Expecting the operating system to keep local variables after the area goes out of scope is just begging for errors later on when the compiler/os treatment of said areas changes. On 6/4/2023 1:37 PM, Steve Litt via fpc-pascal wrote: Henry Vermaak via fpc-pascal said on Fri, 2 Jun 2023 09:38:17 +0100 On Fri, 2 Jun 2023 at 01:36, Steve Litt via fpc-pascal wrote: fillchar(junkvar, junkvar_size, 'b'); person := modperson(person, 'Martin'); person := modperson(person2, 'Maria'); Maybe a typo? (E.g. person2 := modperson(person2, 'Maria')) Henry Thanks Henry! You're right: Changing the second person := to person2 := did just what I wanted it to do. Because returning a local array or string as a function return in C leads to horrible intermittents due to the local going out of scope and relinquishing the local's stack, which can then be overwritten, I added a procedure, a function, and a main program statement which each consumed two million bytes of local variables, and the person and person2 didn't get overwritten. Very cool. When I increased the huge local vars to three million bytes, the program segfaulted. I figure I just ran it out of stack, but until I did, the huge local vars didn't trash the contents of person and person2. Thanks for your help. SteveT Steve Litt Autumn 2022 featured book: Thriving in Tough Times http://www.troubleshooters.com/bookstore/thrive.htm ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
On 04/06/2023 17:49, Martin via fpc-pascal wrote:
On 04/06/2023 15:04, Juha Manninen via fpc-pascal wrote:
Why the following code fails to compile?
MyObj.RecInstance.ii := 123;
Technically you can modify the members of the temp record (just to
have the work thrown away afterwards).
So I guess the compiler forbids it, because the only case it would
ever be done is: by mistake.
Btw, this works (or actually not, it works wrong)
with MyObj.RecInstance do {begin} ii := 123; {end;}
Now you could do some work with the temp result, and have it trashed at
the end of the "with" block.
However, fpc incorrectly changes the value in the original record.
Yet, don't use it. It will (likely) change, and stop working. (or work
correctly, changing the temp value only).
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Re: [fpc-pascal] Error: Argument cannot be assigned to
On 04/06/2023 15:04, Juha Manninen via fpc-pascal wrote: Why the following code fails to compile? TMyRec = record ... property RecInstance: TMyRec read fRecInstance;// write fRecInstance; ... MyObj.RecInstance.ii := 123; Access through property seems to be the problem. Accessing fRecInstance directly works. A property enforces that any code you write will work even if you change the property to a getter/setter. Or in other words, it will fail any code that would not work. If this was a getter, it would be function GetRec: TMyRec; And that returns a *copy* in a temporary location of the record. Technically you can modify the members of the temp record (just to have the work thrown away afterwards). So I guess the compiler forbids it, because the only case it would ever be done is: by mistake. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
On 04/06/2023 15:04, Juha Manninen via fpc-pascal wrote: Why the following code fails to compile? TMyRec = record ... property RecInstance: TMyRec read fRecInstance;// write fRecInstance; ... MyObj.RecInstance.ii := 123; Access through property seems to be the problem. Accessing fRecInstance directly works. A property enforces that any code you write will work even if you change the property to a getter/setter. Or in other words, it will fail any code that would not work. If this was a getter, it would be function GetRec: TMyRec; And that returns a *copy* in a temporary location of the record. Technically you can modify the members of the temp record (just to have the work thrown away afterwards). So I guess the compiler forbids it, because the only case it would ever be done is: by mistake. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
On Sunday, June 4, 2023, Mattias Gaertner via fpc-pascal < fpc-pascal@lists.freepascal.org> wrote: > > Correct. Property RecInstance is read only. > No, I can define it as : property RecInstance: TMyRec read fRecInstance write fRecInstance; and still get the same error. Juha ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
On Sun, 4 Jun 2023 16:04:48 +0300 Juha Manninen via fpc-pascal wrote: > Why the following code fails to compile? > > type > TMyRec = record > ss: String; > ii: Integer; > end; > TMyClass = class > private > fName: String; > fRecInstance: TMyRec; > property > RecInstance: TMyRec read fRecInstance;// write fRecInstance; > end; > var > MyObj : TMyClass; > begin > MyObj := TMyClass.Create; > MyObj.RecInstance.ii := 123; > MyObj.Free; > end. > > Access through property seems to be the problem. Accessing > fRecInstance directly works. Correct. Property RecInstance is read only. Mattias ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Function to create a record ?
Ralf Quint via fpc-pascal said on Thu, 1 Jun 2023 17:43:58 -0700 >On 6/1/2023 5:36 PM, Steve Litt via fpc-pascal wrote: >> >> What is the best way for me to construct newperson() so that every >> time called it would return a new variable? >W.T.F.? > >Sorry, but for how long are you programming, in general, and for how >long in Pascal? > >Seriously, you should take some very basic Pascal tutorials, work >through them, and in particular, pay close attention to the "scope" of >variables as well as parameter passing. You seem to be completely >oblivious to those very basics here... :( > >Ralf Feeling better after getting that off your chest Ralf? My post reveals the outcome of my investigation. SteveT Steve Litt Autumn 2022 featured book: Thriving in Tough Times http://www.troubleshooters.com/bookstore/thrive.htm ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Function to create a record ?
Henry Vermaak via fpc-pascal said on Fri, 2 Jun 2023 09:38:17 +0100 >On Fri, 2 Jun 2023 at 01:36, Steve Litt via fpc-pascal > wrote: >> fillchar(junkvar, junkvar_size, 'b'); >> person := modperson(person, 'Martin'); >> person := modperson(person2, 'Maria'); > >Maybe a typo? (E.g. person2 := modperson(person2, 'Maria')) > >Henry Thanks Henry! You're right: Changing the second person := to person2 := did just what I wanted it to do. Because returning a local array or string as a function return in C leads to horrible intermittents due to the local going out of scope and relinquishing the local's stack, which can then be overwritten, I added a procedure, a function, and a main program statement which each consumed two million bytes of local variables, and the person and person2 didn't get overwritten. Very cool. When I increased the huge local vars to three million bytes, the program segfaulted. I figure I just ran it out of stack, but until I did, the huge local vars didn't trash the contents of person and person2. Thanks for your help. SteveT Steve Litt Autumn 2022 featured book: Thriving in Tough Times http://www.troubleshooters.com/bookstore/thrive.htm ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
Formatting was a little weird. This is what I meant, but the error remains : type TMyRec = record ss: String; ii: Integer; end; TMyClass = class private fName: String; fRecInstance: TMyRec; public property RecInstance: TMyRec read fRecInstance;// write fRecInstance; end; var MyObj : TMyClass; begin MyObj := TMyClass.Create; MyObj.RecInstance.ii := 123; MyObj.Free; end. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Error: Argument cannot be assigned to
Compiler version is FPC 3.2.2 on Linux. Juha ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
[fpc-pascal] Error: Argument cannot be assigned to
Why the following code fails to compile? type TMyRec = record ss: String; ii: Integer; end; TMyClass = class private fName: String; fRecInstance: TMyRec; property RecInstance: TMyRec read fRecInstance;// write fRecInstance; end; var MyObj : TMyClass; begin MyObj := TMyClass.Create; MyObj.RecInstance.ii := 123; MyObj.Free; end. Access through property seems to be the problem. Accessing fRecInstance directly works. Juha ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
[fpc-pascal] Choice of exceptions to use?
Hi, I'm working on code where the function take a (x, y) set of coordinates. If the coordinates are out of range/bounds, I want to raise an exception with a message explaining the reason and limits. I definitely don't want to "silently do nothing". Looking at these set of built-in exceptions: https://www.freepascal.org/docs-html/rtl/sysutils/index-4.html I'm in two-minds as to which exception to raise. Seems my choices are: * EArgumentException - an invalid argument was passed to the method * ERangeException - I could interpret this as the values passed in, were not in the allowed range. Initially I was leaning towards the Range exception, but now I'm thinking that maybe the Argument exception is more appropriate (based on the descriptions seen in the linked docs). What's your thoughts? Regards, Graeme ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
