Re: [fpc-pascal] Basic question about TStringList
From: [EMAIL PROTECTED] As a consequence I have another question. Suppose I have a function that returns a TStringList: Myfunction(): TStringList; I must have inside a line like: Result:=TStringList.Create; Let A be a TStringList, I have two ways to catch the result of my function: A:=Myfunction(); or A.Assign(Myfunction()); In the first case, if do A.Free, I release the memory allocated by the function. What's arriving in the second case? I can do A.Free, but does that action will also release the memory allocated by the function? By the way, do you have some tricks to detect this kind of error? This consequence of returning references to newly created objects is a very subtle one and I have seen some spectacular memory leaks caused by this practice. My programming convention is to try to always call .Create and .Free in the same context if possible i.e. procedure Myfunction(const ASL: TStringList); begin // add stuff to ASL end; And in code using this function: SL := TStringList.Create; Myfunction(SL); // do stuff SL.Free; Not quite bullet proof yet, since one can call Myfunction without actually instantiating SL, but at least that should give you a runtime error that should be easy to trace. Regards Christo Crause NOTICE: Please note that this eMail, and the contents thereof, is subject to the standard Sasol eMail legal notice which may be found at: http://www.sasol.com/legalnotices If you cannot access the legal notice through the URL attached and you wish to receive a copy thereof please send an eMail to [EMAIL PROTECTED] ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] Basic question about TStringList
Hi, I seek help to clarify a very basic use of TStringList. Let A and B be TStringLists. What is the difference between: A:=B; and A.Assign(B); ? Thanks in advance for your help, Gilles Marcou ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Basic question about TStringList
Op donderdag 27-03-2008 om 11:35 uur [tijdzone +0100], schreef [EMAIL PROTECTED]: Hi, I seek help to clarify a very basic use of TStringList. Let A and B be TStringLists. What is the difference between: A:=B; and A.Assign(B); ? That's more a basic(?) question about Pascal. When you do A:=B; then A has become equal to B. That means for example that if you add an new string to B, this new string will also be in A. After all A and B are the same. Note that if A contained a TStringList that you can not acces it anymore through A, but it's still present in memory. When you do A.Assign(B); then all strings in A are cleared and afterwards all strings in B are copied to A. Further all relevant properties of B are also set to A. Note that in this case, A should already contain a TStringList, and if you add values to B after the assignment, those strings will not appear in B. Joost ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Basic question about TStringList
Hi, I seek help to clarify a very basic use of TStringList. Let A and B be TStringLists. What is the difference between: A:=B; and A.Assign(B); ? That's more a basic(?) question about Pascal. When you do A:=B; then A has become equal to B. That means for example that if you add an new string to B, this new string will also be in A. After all A and B are the same. Note that if A contained a TStringList that you can not acces it anymore through A, but it's still present in memory. When you do A.Assign(B); then all strings in A are cleared and afterwards all strings in B are copied to A. Further all relevant properties of B are also set to A. Note that in this case, A should already contain a TStringList, and if you add values to B after the assignment, those strings will not appear in B. In other words: When you declare A, B : TStringList; you actually allocated two pointer to TStringList since classes are inherently pointers. When you do A:=B you now have A pointing to the same memory space as B. It's a pity you can't do A^ := B^; Andreas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Basic question about TStringList
Hi, thanks for your very clear answer. In fact this is chilling me as I am thinking to the huge amount of memory leaks that I certainly have in my developements... This means that whenever the assignement operator := is used with TStringLists, the recieving list shall never be created! As a consequence I have another question. Suppose I have a function that returns a TStringList: Myfunction(): TStringList; I must have inside a line like: Result:=TStringList.Create; Let A be a TStringList, I have two ways to catch the result of my function: A:=Myfunction(); or A.Assign(Myfunction()); In the first case, if do A.Free, I release the memory allocated by the function. What's arriving in the second case? I can do A.Free, but does that action will also release the memory allocated by the function? By the way, do you have some tricks to detect this kind of error? Thanks again, Gilles Marcou ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Basic question about TStringList
On 27 Mar 2008, at 13:27, [EMAIL PROTECTED] wrote: Let A be a TStringList, I have two ways to catch the result of my function: A:=Myfunction(); or A.Assign(Myfunction()); In the first case, if do A.Free, I release the memory allocated by the function. What's arriving in the second case? I can do A.Free, but does that action will also release the memory allocated by the function? No. By the way, do you have some tricks to detect this kind of error? Compile with -ghl Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
