BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Help with CBuilder typedef for Delphi DLL function          BorlandTalk.com Forum Index -> C++ Builder (ActiveX) View previous topic :: View next topic   Author Message Kevin Buckle Guest Posted: Wed Jun 23, 2004 3:26 am    Post subject: Help with CBuilder typedef for Delphi DLL function Hi all I have to use functions from a third-party DLL in a CBuilder application. I presume the DLL is written in Delphi - all I have is a list of the function declarations within the DLL. I can successfully use most of the functions but one is proving to be a real problem. The function in question is defined as: function GetNewValue(ID,Start,End:PChar; var Value:TBStr):Integer What should I use for the TBStr data-type? My typedef currently looks like this: typedef int (__stdcall *pDLL_GetNewValue) (char*,char*,char*,AnsiString*); I'm sure I shouldn't be using an AnsiString here (should I?) but it's the only way it works. I've had no success using WideString, BSTR or char* instead but I may be doing it incorrectly. Unfortunately, after several calls to this function I get an AV on the call. It is the only DLL call which causes a problem and it is the only one with a TBStr parameter. I'm using: ... pDLL_GetNewValue DLL_GetNewValue; ... result = DLL_GetNewValue(szID,szStart,szEnd,&asValue); for the function call. Is anyone able to offer any help? Many thanks Kevin Back to top Remy Lebeau (TeamB) Guest Posted: Wed Jun 23, 2004 7:57 am    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Kevin Buckle" <kevin.buckle (AT) nospam (DOT) co.nz> wrote Quote: What should I use for the TBStr data-type? BSTR, except in this case the original parameter is declared using 'var' so it would be BSTR* instead, ie: typedef int (__stdcall *pDL_GetNewValue)(char*, char*, char*, BSTR*); Quote: I've had no success using WideString, BSTR or char* instead but I may be doing it incorrectly. Please show the actual code you have tried using WideString or BSTR which did not work for you. Quote: Unfortunately, after several calls to this function I get an AV on the call. Again, please show your actual code. Also, is the original function actually declared using 'stdcall'? If not, then you need to use __fastcall instead of ___stdcall in your typedef. Quote: result = DLL_GetNewValue(szID,szStart,szEnd,&asValue); What is asValue declared as? Your naming convention suggests an AnsiString. Gambit Back to top Kevin Buckle Guest Posted: Thu Jun 24, 2004 1:44 am    Post subject: Re: Help with CBuilder typedef for Delphi DLL function Yes - I originally used the declaration you suggested using BSTR*. This didn't produce any AVs but I was unable to decipher the returned value. See the example below. Unfortunately I have no access to the DLL function code to check the actual function declarations. I tried __fastcall originally and that gave an AV every time any of the functions were called. All the other functions from the DLL work fine using __stdcall so I stuck with this. Yes again, asValue is declared as an AnsiString in the example I gave in the original post. This is an example of a test attempt using BSTR* and WideString: typedef int (__stdcall *pDLL_GetNewValue)(char*, char*, char*, BSTR*); .... EDLL_Result Result; // enumerated type for DLL integer return codes WideString wsValue; // time of maximum value in period (in form "hh:nn") bool Finished=false; while (!Finished) { // loop forever until AV Result = DLL_GetNewValue("temperature","12:45","15:00",&wsValue); // display wsValue - how? Sleep(300); } This all works fine (no AV's after thousands of repeated calls) except I have been unable to decipher the returned text in the wsValue parameter. Maybe this is my real problem? I tried AnsiString(wsValue) but I just get question marks in the string. Using AnsiString* in the typedef and passing in a &AnsiString I get "13:00" returned in the AnsiString (which is the correct result). I guess there must be something I have to do with the returned WideString before I can read it and display it? Passing a WideString into a function expecting a BSTR works fine: in the function I can convert the passed value back into a WideString and then straight into an AnsiString for display in a TLabel. It's reading the return value from a BSTR* parameter that's the problem. I'm going to do some work on this and will post a small sample of code with my findings. Thanks for your help, it's much appreciated. Kevin "Remy Lebeau (TeamB)" <gambit47.no.spam (AT) no (DOT) spam.yahoo.com> wrote Quote: "Kevin Buckle" <kevin.buckle (AT) nospam (DOT) co.nz> wrote in message news:40d8f8db$1 (AT) newsgroups (DOT) borland.com... What should I use for the TBStr data-type? BSTR, except in this case the original parameter is declared using 'var' so it would be BSTR* instead, ie: typedef int (__stdcall *pDL_GetNewValue)(char*, char*, char*, BSTR*); I've had no success using WideString, BSTR or char* instead but I may be doing it incorrectly. Please show the actual code you have tried using WideString or BSTR which did not work for you. Unfortunately, after several calls to this function I get an AV on the call. Again, please show your actual code. Also, is the original function actually declared using 'stdcall'? If not, then you need to use __fastcall instead of ___stdcall in your typedef. result = DLL_GetNewValue(szID,szStart,szEnd,&asValue); What is asValue declared as? Your naming convention suggests an AnsiString. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Thu Jun 24, 2004 2:11 am    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Kevin Buckle" <kevin.buckle (AT) nospam (DOT) co.nz> wrote Quote: Unfortunately I have no access to the DLL function code to check the actual function declarations. I suggest you find a way to getaccess, because that seems to be the root of the problem - you are obviously mangling something up somewhere. Where did you get the original Delphi declarations from? Quote: Yes again, asValue is declared as an AnsiString in the example I gave in the original post. You did not show the actual declaration for asValue in your original posting, hense my earlier comments. Quote: WideString wsValue; // time of maximum value in period (in form You are declaring the WideString outside of the while() loop. Quote: Result = DLL_GetNewValue("temperature","12:45","15:00",&wsValue); You are then retreiving a value from the function into the WideString, but you are not clearing the previous WideString value first. You are going to leak memory that way since the BSTR stored inside the WideString won't get freed properly. You should either move the WideString into the loop so that it goes out of scope each time and is freed automatically, or else call the WideString's Empty() method before than calling the DLL function. Quote: // display wsValue - how? WideString can be used pretty much anywhere that expects an AnsiString. Thus you can use it for ShowMessage(), MessageDlg(), component captions, etc. just like you would with AnsiString. AnsiString has a conversion constructor that accepts WideString and will convert the BSTR data into char* data accordingly. Quote: Using AnsiString* in the typedef and passing in a &AnsiString I get "13:00" returned in the AnsiString (which is the correct result). That suggests then that the function is actually returning a char* string even though it is declared to return a BSTR string instead. The two are not the same thing, so the function behavior is in contradiction to its declaration. Quote: It's reading the return value from a BSTR* parameter that's the problem. Please show a more complete code snippet that shows exactly what you are doing. Gambit Back to top Kevin Buckle Guest Posted: Thu Jun 24, 2004 3:33 am    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Remy Lebeau (TeamB)" <gambit47.no.spam (AT) no (DOT) spam.yahoo.com> wrote Quote: I suggest you find a way to getaccess, because that seems to be the root of the problem - you are obviously mangling something up somewhere. Where did you get the original Delphi declarations from? Working on that - original declarations listed in an htlm help file included in the application folder where the DLL sits. The DLL is shipped with a large, complex application that uses a proprietary database for data storage. The DLL is intended to provide third-party access to the data. Have contacted the application vendor for assistance. Quote: You are declaring the WideString outside of the while() loop. Yes - this was just a quick test I set up and I overlooked that. Doesn't affect the result though (apart from the obvious memory leak). Quote: WideString can be used pretty much anywhere that expects an AnsiString. Thus you can use it for ShowMessage(), MessageDlg(), component captions, etc. just like you would with AnsiString. AnsiString has a conversion constructor that accepts WideString and will convert the BSTR data into char* data accordingly. Unfortunately I'm already familiar with this which leads to your next comment ... Quote: That suggests then that the function is actually returning a char* string even though it is declared to return a BSTR string instead. The two are not the same thing, so the function behavior is in contradiction to its declaration. That's more or less what I had concluded - hence my original post. I should have been more clear at the outset. Quote: Please show a more complete code snippet that shows exactly what you are doing. For the moment I'm just trying to read the returned WideString parameter into a label. It's about as simple as I can make it. The following displays "???" in the label: typedef int (__stdcall *pDLL_GetNewValue) (char*,char*,char*,BSTR*); pDLL_GetNewValue DLL_GetNewValue; WideString wsValue; DLL_GetNewValue("temperature","12:45","15:00",&wsValue); lblReturnedText->Caption = AnsiString(wsValue); And this displays "13:00" in the label. typedef int (__stdcall *pDLL_GetNewValue) (char*,char*,char*,AnsiString*); pDLL_GetNewValue DLL_GetNewValue; AnsiString asValue; DLL_GetNewValue("temperature","12:45","15:00",&asValue); lblReturnedText->Caption = asValue; I assumed that I couldn't use BSTR* for the TBSTR parameter due to the results I had in the test code above or that I had a fundamental misunderstanding of BSTR and WideString. I may just have to wait for some info from the DLL author(s). Once again, thanks for your time and assistance. Kevin Back to top Remy Lebeau (TeamB) Guest Posted: Thu Jun 24, 2004 7:34 am    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Kevin Buckle" <kevin.buckle (AT) nospam (DOT) co.nz> wrote Quote: typedef int (__stdcall *pDLL_GetNewValue) (char*,char*,char*,BSTR*); pDLL_GetNewValue DLL_GetNewValue; WideString wsValue; DLL_GetNewValue("temperature","12:45","15:00",&wsValue); lblReturnedText->Caption = AnsiString(wsValue); There is nothing wrong with that code, assuming the DLL function actually returns a BSTR to begin with. Quote: AnsiString asValue; DLL_GetNewValue("temperature","12:45","15:00",&asValue); That is dangerous code. AnsiString has specific requiremenets for how its memory is handled internally. You can't just allocate a character array and then assign it to the AnsiString's internals directly. The only way that code could be safe is if the DLL function is returning an actual AnsiString, not a raw char* string. Quote: I assumed that I couldn't use BSTR* for the TBSTR parameter due to the results I had in the test code above var TBStr = BSTR* Gambit Back to top Kevin Buckle Guest Posted: Thu Jun 24, 2004 9:07 pm    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Remy Lebeau (TeamB)" <gambit47.no.spam (AT) no (DOT) spam.yahoo.com> wrote Quote: AnsiString asValue; DLL_GetNewValue("temperature","12:45","15:00",&asValue); That is dangerous code. AnsiString has specific requiremenets for how its memory is handled internally. You can't just allocate a character array and then assign it to the AnsiString's internals directly. The only way that code could be safe is if the DLL function is returning an actual AnsiString, not a raw char* string. Agreed! The AV's and memory leakage experienced using this version suggest that the DLL is *not* returning an AnsiString. Quote: var TBStr = BSTR* I found this definition of TBStr on the MSDN site - concerning .NET framework class library (the only place on the web I could find any reference to a TBStr). "TBStr (Supported by the .NET Compact Framework) - A length-prefixed, platform-dependent char string. ANSI on Windows 98, Unicode on Windows NT. - You rarely use this BSTR-like member." Is this a completely different data type with a coincidentally identical name? It seems to explain the behaviour I'm seeing. It's a char string (rather than a widestring) but it's length prefixed. I'm passing in a (pointer to) BSTR (wchar based) which the DLL treats as char based and returns a (pointer to) length-prefixed char string, which seems to keep the memory management happy but obviously it's not a "real" BSTR so the conversion back to an AnsiString in my app gives rubbish? Does that make any sense? I'm not really sure what I mean myself - I'll have to give it some more thought If so, maybe I can extract the correct string from the returned BSTR? The definition from the MSDN site suggests that I shouldn't be using a BSTR in place of the TBStr parameter. This seems odd anyway - why wouldn't the function just use BStr* rather than TBStr* (there is a BStr type in Delphi isn't there?). Back to top Remy Lebeau (TeamB) Guest Posted: Thu Jun 24, 2004 9:18 pm    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Kevin Buckle" <kevin.buckle (AT) nospam (DOT) co.nz> wrote Quote: Agreed! The AV's and memory leakage experienced using this version suggest that the DLL is *not* returning an AnsiString. If it is an ActiveX DLL, then it should be returning a BSTR. Your earlier observations suggest otherwise, though. Quote: I found this definition of TBStr on the MSDN site All of Microsoft's stuff applies to C++, not Pascal. In any case, TBStr is declared in the VCL's ole2 unit as the following: POleStr = PWideChar; TBStr = POleStr; Which translates to the following in ole2.hpp for C++: typedef wchar_t *TBStr; For most intents and purposes, that is correct (BSTR is slightly more complicated than just being a simple wchar_t* string, though). Quote: Is this a completely different data type with a coincidentally identical name? It seems to explain the behaviour I'm seeing. Is the DLL in question designed for use with .NET? Which OS are you actually running your code under at the time the string returns gibberish when treated as BSTR? Gambit Back to top Alan Bellingham Guest Posted: Thu Jun 24, 2004 11:18 pm    Post subject: Re: Help with CBuilder typedef for Delphi DLL function "Remy Lebeau (TeamB)" <gambit47.no.spam (AT) no (DOT) spam.yahoo.com> wrote: Quote: For most intents and purposes, that is correct (BSTR is slightly more complicated than just being a simple wchar_t* string, though). This may bear expanding. A BSTR is indeed a wchar_t* pointer. However, it doesn't point at the start of the memory that was allocated, but along a bit, at the start of the wide character data itself. Before that is a length count: --------------------------------------------------------- Quote: Len | ch | ch | ch | ch | ... --------------------------------------------------------- ^ ^ Quote: | `-- what the user sees as the start What the underlying code knows is the start So, when SysAllocString is called, memory is allocated from the OS. The pointer is then incremented before being returned. When SysFreeString is called, the reverse happens - the pointer is decremented before the memory is released to the OS. When SysStringLen is called by a client to discover the string length, it just looks at the place before the string data to find the answer. This means that BSTRs do not have to use null terminators to get things right - they may have embedded nulls if desired. The outcome of this is that passing a raw wchar_t* into a routine that wants a BSTR may work, or it may not. It will blow up in very bad ways if the routine does SysStringLen to find out how long the string actually is. Since this is a pretty sensible thing for the client to want to do, beware. Alan Bellingham -- Team Thai Kingdom <url:http://www.borland.com/newsgroups/> Borland newsgroup descriptions <url:http://www.borland.com/newsgroups/netiquette.html> netiquette Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         BorlandTalk.com Forum Index -> C++ Builder (ActiveX) All times are GMT Page 1 of 1   Jump to: Select a forum C++ Builder Newsgroups----------------C++ BuilderC++ Builder (ActiveX)C++ Builder (Announcements)C++ Builder (Command Line Tools)C++ Builder DatabasesC++ Builder Databases (ADO)C++ Builder Databases (Desktop)C++ Builder Databases (InterBase Express)C++ Builder Databases (Multi-Tier)C++ Builder Databases (SQL Servers)C++ Builder (Graphics)C++ Builder (IDE)C++ Builder (Internet)C++ Builder (Internet Socket)C++ Builder (Internet Web)C++ Builder (Jobs)C++ Builder (Language)C++ Builder (Language C++)C++ Builder (Compatibility with MFC)C++ Builder (Native API)C++ Builder (Non-Technical)C++ Builder (Students)C++ Builder (Third Party Tools)C++ Builder (Upgrade)C++ Builder (VCL)C++ Builder (VCL Components Usage)C++ Builder (VCL Components Development)C++ Builder (VCL Usage)C++ Builder (WinAPI)C++ Builder Installation Delphi Newsgroups----------------Delphi (General)Delphi ActiveX Controls UsageDelphi ActiveX Controls DevelopmentDelphi As400Delphi DatabasesDelphi Databases (ADO)Delphi Databases (dbExpress)Delphi Databases (Desktop)Delphi Databases (InterBase Express)Delphi Databases (Multi-Tier)Delphi Databases (SQL Servers)Delphi DeploymentDelphi GraphicsDelphi IDEDelphi InternationalizationDelphi InternetDelphi Internet Isapi-WebBrokerDelphi Internet WebSnapDelphi Internet WinsockDelphi JobsDelphi Language BASMDelphi Language ObjectPascalDelphi Model Driven Architecture (General)Delphi Model Driven Architecture (Third Party)Delphi MultimediaDelphi Native APIDelphi Non-TechnicalDelphi ObjectPascalDelphi OLE AutomationDelphi OO designDelphi OpenToolsAPIDelphi Reporting-ChartingDelphi RTLDelphi StudentsDelphi TeamSourceDelphi Thirdparty ToolsDelphi Thirdparty Tools (General)Delphi Thirdparty Tools (IntraWeb)Delphi Thirdparty Tools (RaveReports)Delphi UpgradeDelphi VCLDelphi VCL ComponentsDelphi VCL Components UsingDelphi VCL Components WritingDelphi WebServices SOAPDelphi WinAPIDelphi XMLDelphi Installationcomp.lang.pascal.delphi.components.misccomp.lang.pascal.delphi.components.usagecomp.lang.pascal.delphi.components.writingcomp.lang.pascal.delphi.databasescomp.lang.pascal.delphi.misccomp.sources.delphi JBuilder Newsgroups----------------JBuilderJBuilder AnnouncementsJBuilder Applet IssuesJBuilder As400JBuilder CompilerJBuilder CORBA/RMIJBuilder DatabasesJBuilder DB SwingJBuilder DebuggerJBuilder DeploymentJBuilder DocumentationJBuilder EnterpriseJBuilder HandheldJBuilder IDEJBuilder JavaJBuilder JavaAPIJBuilder Java LanguageJBuilder Java SwingJBuilder Java BeansJBuilder Java Beans UsageJBuilder Java Beans DevelopmentJBuilder JBCLJBuilder JDataStoreJBuilder JobsJBuilder LinuxJBuilder MacintoshJBuilder & MobileSetJBuilder MultiLingual AppsJBuilder Non-TechnicalJBuilder OpenToolsJBuilder Servlets (JSP)JBuilder StudentsJBuilder Team DevelopmentJBuilder Thirdparty ToolsJBuilder UpgradeJBuilder Installation InterBase Newsgroups----------------InterBaseInterBase Bug DiscussionInterBase GeneralInterBase IBConsoleInterBase OpenSourceInterBase ReplicationInterBase SQLInterBase ThirdpartyInterBase Installation Miscellaneous Borland Newsgroups----------------AppCenterAppServerEnteraVisiBroker  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.