SetLength() is not reliable?

[senglit]

I have several dynamic arraies of record in my program. All of the records have some members of string. I use SetLength to resize these arries in my program. And I found those arries who were been resized for around 10 times (the size grow 1 each time) are ok. but others who are resized for more than 40 times (size grow from 0 to 40+), the program throw a memory violation and crushed.

Is SetLength() reliable? or there are somewhere I can set the stack size (or something other) to avoid this kind of crush?

[julkas]

Is SetLength() reliable?

Yes it is.
Please give more details about , provide code example (source).

[Handoko]

My programs use SetLength, so far it woks perfectly.

[Thaddy]

Woks?
Yes it cooks fine and taste good too 
serious: I am not aware setlength() has problems. That would have showed up may moons before.

Note that increasing length continuously by one is a problem (of the programmer): every time a relocation is not sane programming.

[Martin_fr]

And I found those arries who were been resized for around 10 times (the size grow 1 each time) are ok. but others who are resized for more than 40 times (size grow from 0 to 40+), the program throw a memory violation and crushed.

SetLength is fine. You seem to simply run out of memory.

The short answer: Use TStringList (for strings, otherwise TList or similar), instead of array.

The long answer:
If you do "SetLength(MyArray, length(MyArray)+1);" (or any other value instead of +1)
Then the old memory is "freed" That is, the old memory is added to a pool of "memory that can be re-used". So in your OS you will not see memory shrinking (doing so would be slower).

If you do a lot of such "SetLength", then they will all add there old memory to that pool. They will try to re-use memory from that pool too. But that pool can become fragmented. Then it has lots of small bits of memory (summing up to a huge amount), each to small to be re-used.... => And your app keeps using new mem, until there is none left.

So instead of doing 10 times "+1", you should do 1 time "+10". Pre-allocate what you will need later.
TList/TStringList have that build in (it's called capacity).

[senglit]

there is the main part of the code:

Code: Pascal  [Select][+][-]

1. type
2.   PRecDevInfo=^RecDevInfo;
3.   RecDevInfo = record  
4.     DevId:integer;
5.     Name:string;
6.     Model:string;
7.     ConnTo:string;
8.     ComPort: integer;
9.     ComListId:integer;
10.     Page:integer;      
11.     dType:integer;    
12.     Addr: integer;
13.     IsOn:boolean;
14.     PlcData:array[1..8] of char;
15.     PlcAddr:array[1..8] of integer;
16.     Value1:real;
17.     Value2:real;
18.     Range1:real;
19.     Range2:real;
20.   end;          
21.  
22. var
23.   DevCount:integer=0;
24.   MyDev:array of RecDevInfo;    
25.  
26. function TFrmMain.LoadCmdFile():boolean;
27. var
28.   MyIniFile:TextFile;  
29.   LineNow:integer=0;
30.   s,tmp:string;
31.   strs:TStrings;                                                    
32. begin
33.   SetLength(MyDev,1);    
34.   MyDev[0].Name:='head';
35.   MyDev[0].IsOn:=false;
36.   MyDev[0].DevId:=0;
37.   MyDev[0].Model:='empty';
38.   AssignFile(MyIniFile,'sys.pzwj');
39.   Reset(MyIniFile);
40.   strs:=TStringList.Create;  
41.   try
42.     while not eof(MyIniFile) do
43.       begin
44.         inc(LineNow);
45.         Readln(MyIniFile,s);    
46.       s:=UpperCase(Trim(s));
47.       if Length(s)=0 then continue;
48.       if leftStr(s,1)='#' then continue;
49.       strs.DelimitedText:=s;
50.       strs.Delimiter:=#9;
51. //check here, if the format of MyIniFile is wrong ,return false
52.           inc(DevCount);
53.           SetLength(MyDev,DevCount+1);          
54.           MyDev[DevCount].DevId:=DevCount;
55.           MyDev[DevCount].Name:=strs[0];
56.           MyDev[DevCount].ComPort:=StrToInt(strs[1]);
57.           MyDev[DevCount].Addr:=StrToInt(strs[2]);
58.           MyDev[DevCount].Model:=strs[3];
59.           MyDev[DevCount].Page:=strtoint(strs[4]);
60.           MyDev[DevCount].dType:=strtoint(strs[5]);
61.           MyDev[DevCount].ConnTo:=strs[6];
62.           MyDev[DevCount].IsOn:=false;
63.           ...... the strs.count may go to 20
64.     end;
65.   finally
66.     CloseFile(MyIniFile);
67.   end;
68.   result := true;
69. end;              
70.  

After I declear the array MyDev as "MyDev:array[0..127] of RecDevInfo;" and not use setlength, it goes ok. What's the wrong thing did I do?

[Thaddy]

After I declear the array MyDev as "MyDev:array[0..127] of RecDevInfo;" and not use setlength, it goes ok. What's the wrong thing did I do?

Ah, much simpler than you explained before:

You can not call setlength() on a static array, only on dynamic arrays. MyDev:array[0..127] is a static array, not a dynamic array......

Code: Pascal  [Select][+][-]

1. var
2.   MyDev:array of RecDevInfo; //dynamic array
3. begin
4.   Setlength(MyDev:array, 128); // set the size to 128

Should solve it.

[rvk]

After I declear the array MyDev as "MyDev:array[0..127] of RecDevInfo;" and not use setlength, it goes ok. What's the wrong thing did I do?

Ah, much simpler than you explained before:

You can not call setlength() on a static array, only on dynamic arrays. MyDev:array[0..127] is a static array, not a dynamic array......

That's NOT what (s)he said.

If you read carefully it says running it with a static array, it all works ("when NOT using setlength").
I highlighted the part for you in the quoted post.

The question would by, "Why does SetLength() crap out with just 128 iterations of +1".

But that could depend on the size of the record.

(And you're correct in saying +1 in a loop isn't good programming practice, as explained earlier)

[Thaddy]

After I declear the array MyDev as "MyDev:array[0..127] of RecDevInfo;" and not use setlength, it goes ok. What's the wrong thing did I do?

Ah, much simpler than you explained before:

You can not call setlength() on a static array, only on dynamic arrays. MyDev:array[0..127] is a static array, not a dynamic array......

That's NOT what (s)he said.

If you read carefully it says running it with a static array, it all works ("when NOT using setlength").
I highlighted the part for you in the quoted post.

I read it and interpreted it and tested it, Rik.  This is what one means.
Furthermore his/hers inc() is premature... should after . Likely also  the case.

[rvk]

I read it and interpreted it and tested it, Rik.  This is what one means.

One never said SetLength is called on a static array.

One said, when using a static array "and NOT using SetLength", all works correctly.

[Thaddy]

Look at the place of the inc() in that case.... initialized to 0, should be -1 or performed later in the code. It is really bad code anyway, but therefor we put the time in...

[FTurtle]

DevCount is global initialized variable that permanently grows.
What is it?!

[FTurtle]

Code: Pascal  [Select][+][-]

1.       strs.DelimitedText:=s;
2.       strs.Delimiter:=#9;
3.  

Does it really work?

1. First set Delimiter and only after - DelimitedText (the text which will processed with respect of setted earlier Delimiter)
2. Check strs.Count before things like MyDev[DevCount].ConnTo:=strs[6];

[munair]

Note that increasing length continuously by one is a problem (of the programmer): every time a relocation is not sane programming.

There are situations where increasing by one is the only solution. You only need to take a look at UTF8LowerCase() where it is used extensively. Here is a snippet from that function:

Code: Pascal  [Select][+][-]

1. begin
2.           p:=OutStr - PChar(Result);
3.           SetLength(Result,Length(Result)+1);// Increase the buffer
4.           OutStr := PChar(Result)+p;
5.           OutStr^ := #$C4;
6.           inc(OutStr);
7.           OutStr^ := #$B1;
8.           dec(CounterDiff);
9.         end

AFAIK even with large texts, it doesn't give any problems (as long as there is enough memory).

[Handoko]

@senglit

Can you please provide the source code that we can compile and test? Usually with compile-able code to test and inspect, I can debug and find the trouble line in hours. So do the many other seniors here.

Create a new folder, copy and paste all the necessary files except: the binary (exe file), *.bak, lib and backup folders. Compress the folder and send the zip file here. If you're not willing to publicize your project, you can write a demo that shows the issue.

Woks?
Yes it cooks fine and taste good too 

I was in the middle of having my meal when posting the post, so I unconsciously typed the word related with it.