C / C++ / MFC

FirstPrevNext

Memory leak when return char* from DLL Shivanand Gupta30-Mar-09 22:13 Shivanand Gupta 30-Mar-09 22:13  Hi , I have a problem of memory leak when we call a function from win 32 DLL in our MFC program. DLL is C type and return value of my DLL is Char* and it is locally defined in function of DLL. and size is 1024 byte. when functon call four times then MFC application hold 4 KB Extra memory. Re: Memory leak when return char* from DLL Rajesh R Subramanian30-Mar-09 22:16 Rajesh R Subramanian 30-Mar-09 22:16  Is the DLL allocating memory that the char* points to, on the heap? Probably then the calling application must free this memory up? Do you have any docs for that DLL? Or if you have the source code, you may verify this. It is a crappy thing, but it's life -^ Carlo Pallini Re: Memory leak when return char* from DLL Shivanand Gupta30-Mar-09 23:18 Shivanand Gupta 30-Mar-09 23:18  i m using New and Delete in calling application(MFC). but "delete []cData;" line have error runtime. if we use cData='\0' and after this "delete []cData;" then memory leak still continue. how can free memory in MFC application. Re: Memory leak when return char* from DLL Rajesh R Subramanian30-Mar-09 23:32 Rajesh R Subramanian 30-Mar-09 23:32  If the memory is allocated with new in the DLL, then clean it up with delete after you've used the data. Where is the difficulty? I don't see anything more to 'discuss' about here. It is a crappy thing, but it's life -^ Carlo Pallini Re: Memory leak when return char* from DLL Shivanand Gupta31-Mar-09 0:15 Shivanand Gupta 31-Mar-09 0:15  Actually i am using static linking a dll. so when we used delete then runtime error occor about heap Re: Memory leak when return char* from DLL Akt_4_U30-Mar-09 22:18 Akt_4_U 30-Mar-09 22:18  When returning char* as return value, you must allocate memory in heap(using malloc or new), from your DLL and deallocate this memory(free or delete) after usage from the calling applciation. prvn Re: Memory leak when return char* from DLL Shivanand Gupta30-Mar-09 23:16 Shivanand Gupta 30-Mar-09 23:16  i m using New and Delete in calling application(MFC). but "delete []cData;" line have error runtime. if we use cData='\0' and after this "delete []cData;" then memory leak still continue. Re: Memory leak when return char* from DLL Iain Clarke, Warrior Programmer30-Mar-09 23:44 Iain Clarke, Warrior Programmer 30-Mar-09 23:44  shivanandgupta wrote: if we use cData='\0' and after this "delete []cData;" then memory leak still continue. That should not be a surprise... Either you are just making a silly mistake (which we all do), or it's a bit more complex and you are allocating and freeing from different heaps. This could happen if you statically link to the C++ runtime. One simple choice would be to use IMalloc to allocate / free chunks of memory. Look at CoGetMalloc etc for documentation. I still think it's likely to be something dumb... Are you sure the memory is not already freed elsewhere? Iain. In the process of moving to Sweden for love (awwww). If you're in Scandinavia and want an MVP on the payroll (or happy with a remote worker), give me a job! Re: Memory leak when return char* from DLL Shivanand Gupta31-Mar-09 0:17 Shivanand Gupta 31-Mar-09 0:17  Thanks for Reply i am calling DLL statically Re: Memory leak when return char* from DLL Shivanand Gupta31-Mar-09 1:04 Shivanand Gupta 31-Mar-09 1:04  i don't have any idea to use Imalloc and cogetmalloc function to free memory. i m using statically DLL not a COM Re: Memory leak when return char* from DLL Niklas L1-Apr-09 1:46 Niklas L 1-Apr-09 1:46  shivanandgupta wrote: if we use cData='\0' and after this "delete []cData;" then memory leak still continue. Well, if you set cData to '\0' you are manipulating the pointer, not the data it contains. cData is set to null, and that is what you try to delete (and it always succeeds.) Doesn't the DLL supply an API for freeing this string? IMHO dll's should always be designed that way. home Re: Memory leak when return char* from DLL Shivanand Gupta1-Apr-09 20:41 Shivanand Gupta 1-Apr-09 20:41  if we use delete without using '\0' then problem occur about heap at run time. Re: Memory leak when return char* from DLL Niklas L2-Apr-09 3:18 Niklas L 2-Apr-09 3:18  Well, setting it to '\0' is the same as setting it to NULL. In either case, it makes the delete call a no-op, and that's why you don't get a crash, but you DO get a memory leak. home Re: Memory leak when return char* from DLL Dominik Reichl31-Mar-09 1:33 Dominik Reichl 31-Mar-09 1:33  If the DLL allocates the memory using new, it should also be the one to delete[] it. So, let the DLL export a new function to free memory. In your MFC program, you'd call the original method to allocate the char*, and afterwards you'd pass this pointer to the freeing function of the DLL, which would just delete[] it. Too many passwords to remember? Try KeePass Password Safe! Re: Memory leak when return char* from DLL Rolf Kristensen31-Mar-09 9:17 Rolf Kristensen 31-Mar-09 9:17  If the application is being build with the runtime libary (CRT) as a DLL (Recommended by Microsoft), then it should be possible to delete memory in the application that have been allocated by the DLL. Re: Memory leak when return char* from DLL Dominik Reichl31-Mar-09 10:00 Dominik Reichl 31-Mar-09 10:00  Correct. Based on the original question and replies, it was my impression that different heaps/CRTs are being used (see static linkage post), that's why I suggested this way. Of course, using only one CRT will solve the problem, too. Too many passwords to remember? Try KeePass Password Safe! Re: Memory leak when return char* from DLL Shivanand Gupta31-Mar-09 18:36 Shivanand Gupta 31-Mar-09 18:36  I m unable to use CRT can u give some kind of code Re: Memory leak when return char* from DLL Rolf Kristensen31-Mar-09 23:04 Rolf Kristensen 31-Mar-09 23:04  Just follow what Dominik Reichl said in the first comment about ensuring that memory allocated in the DLL is released by the DLL again. Return the char-pointer to the DLL and let the DLL release it again. Re: Memory leak when return char* from DLL Shivanand Gupta1-Apr-09 0:18 Shivanand Gupta 1-Apr-09 0:18  return data char* is locally defined in DLL. so how can release memory of that variable after returning char* variable Re: Memory leak when return char* from DLL Rolf Kristensen1-Apr-09 0:39 Rolf Kristensen 1-Apr-09 0:39  When returning the char* then you take a copy of the char*, but they both point to the same memory in the heap of the DLL. Just pass the copy of the char* from the application to the DLL again, and let the DLL release the memory in its heap. You might consider returning a CString instead of a char*, and ensure that when the CString moves from DLL boundary to the Application boundary that a copy is made of the CString. Re: Memory leak when return char* from DLL Shivanand Gupta1-Apr-09 20:38 Shivanand Gupta 1-Apr-09 20:38  I have try but it is not working. return char* is defined in dll's function as a local variable. it will work well when we defined static variable. but i don't want to create static variable in my DLL. Re: Memory leak when return char* from DLL Rolf Kristensen31-Mar-09 22:59 Rolf Kristensen 31-Mar-09 22:59  Thank you for confirming this. I'm in a situation myself where I'm considering to convert static-libraries into DLL's to improve linker times. The entire application is already using runtime library as DLL, so the conversion should be a matter of exporting all needed classes in the static libraries. win32 Database Paulraj G30-Mar-09 21:40 Paulraj G 30-Mar-09 21:40  Hi... i am creating a application in win32. i need to access the sql or MSAccess databse. but i don't know how to connect win32 application with sql or MSAccess database. please can any one help me? thanking you G.Paulraj Re: win32 Database Stuart Dootson30-Mar-09 22:05 Stuart Dootson 30-Mar-09 22:05  Are you using MFC? If so, then the MFC database connectivity classes[^] will be useful. If you're not using MFC, then the ATL database classes[^] may be useful. Other alternative technologies are ODBC[^], ADO[^] or DAO[^]. They'll all be painful (to some degree) to use with raw C++. Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p Re: win32 Database _AnsHUMAN_ 30-Mar-09 22:07 _AnsHUMAN_ 30-Mar-09 22:07  How about reading about these api's from MSDN SQLHandle,SQLAllocHandle, SQLSetEnvAttr, SQLAllocHandle, SQLConnect, SQLAllocHandle, SQLExecDirec. You need to google first, if you have "It's urgent please" mentioned in your question. _AnShUmAn_

Last Visit: 31-Dec-99 18:00     Last Update: 15-Jun-24 4:49 Refresh ᐊ Prev1...3275327632773278327932803281328232833284 Next ᐅ

General    News    Suggestion    Question    Bug    Answer    Joke    Praise    Rant    Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.