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October 28, 2012 Can't use a C++ class from a DLL | ||||
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I have a DLL with a C++ class and a factory function that creates it. The aim is to load the DLL, get an instance of the class and use it. The interface of the DLL is as follows: ----------------- class IBank { public: virtual const char* APIENTRY getLastError() = 0; virtual const char* APIENTRY getDetail(char* detail) = 0; virtual const bool APIENTRY deposit(unsigned long number, double amount) = 0; virtual const bool APIENTRY withdraw(unsigned long number, double amount) = 0; virtual const double APIENTRY getBalance(unsigned long number) = 0; virtual const bool APIENTRY transfer(unsigned long numberFrom, IBank* bankTo, unsigned long numberTo, double amount) = 0; virtual const bool APIENTRY transferAccept(IBank* bankFrom, unsigned long numberTo, double amount) = 0; }; ----------------- I've followed the instructions given at dlang.org to interface to C/C++ code but got no success. If I use extern(C++) at the place in D code where extern declaration is required I get an access violation when calling any method. On the other hand, if I use extern(Windows, C or Pascal) I can call a method successfully, except that I get wrong return value. The D interface is declared as follows: ----------------- extern (Windows) interface IBank { const char* getLastError(); const char* getDetail(char* detail); const bool deposit(uint number, double amount); const bool withdraw(uint number, double amount); const double getBalance(uint number); const bool transfer(uint numberFrom, IBank* bankTo, uint numberTo, double amount); const bool transferAccept(IBank* bankFrom, uint numberTo, double amount); } export extern (C) IBank Get(); ----------------- And the main program in D that uses the DLL: ----------------- module main; import std.stdio; import core.runtime; import core.sys.windows.windows; import std.string; import std.conv; import ibank; int main() { alias extern(C) IBank function() getBankInstance; FARPROC pDllFunctionVBank, pDllFunctionSberbank; // Load DLL file void* handleVBank = Runtime.loadLibrary("vbank.dll"); void* handleSberbank = Runtime.loadLibrary("sberbank.dll"); if ( (handleVBank is null) || (handleSberbank is null) ) { writeln("Couldn't find necessary DLL files"); return 1; } getBankInstance get1 = cast(getBankInstance) GetProcAddress(handleVBank, "Get".toStringz); getBankInstance get2 = cast(getBankInstance) GetProcAddress(handleSberbank, "Get".toStringz); if ( get1 is null || get2 is null ) { writeln("Couldn't load factory functions"); return 2; } getBankInstance get; IBank vbank = (*get1)(); IBank sberbank = get2(); uint sbnum = 100500; uint vbnum = 128500; writeln("You have an account in Sberbank (100500)"); auto balance = sberbank.getBalance(sbnum); writefln("getBalance(%d) = %s", sbnum, balance); bool res = sberbank.withdraw(sbnum, 500.0); writefln("withdraw(%d, %f) = %s", sbnum, 500.0, res); writeln("You got it!"); ... ----------------- The output I get is (in case I use extern (Windows, C or Pascal)): ----------------- You have an account in Sberbank (100500) getBalance(100500) = -nan got into GenericBank::getBalance() // this is an output from a method called inside the DLL account number = 100500 // inside the DLL balance is 1100 // inside the DLL withdraw(100500, 500.000000) = false You got it! ----------------- |
October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Artie | 28.10.2012 23:52, Artie пишет: > I have a DLL with a C++ class and a factory function that creates it. > The aim is to load the DLL, get an instance of the class and use it. > > The interface of the DLL is as follows: > ----------------- > class IBank > { > public: > virtual const char* APIENTRY getLastError() = 0; > virtual const char* APIENTRY getDetail(char* detail) = 0; > virtual const bool APIENTRY deposit(unsigned long number, > double amount) = 0; > virtual const bool APIENTRY withdraw(unsigned long number, > double amount) = 0; > virtual const double APIENTRY getBalance(unsigned long number) > = 0; > virtual const bool APIENTRY transfer(unsigned long numberFrom, > IBank* bankTo, unsigned long numberTo, double amount) = 0; > virtual const bool APIENTRY transferAccept(IBank* bankFrom, > unsigned long numberTo, double amount) = 0; > }; > ----------------- > > I've followed the instructions given at dlang.org to interface to C/C++ > code but got no success. If I use extern(C++) at the place in D code > where extern declaration is required I get an access violation when > calling any method. On the other hand, if I use extern(Windows, C or > Pascal) I can call a method successfully, except that I get wrong return > value. > > The D interface is declared as follows: > ----------------- > extern (Windows) interface IBank > { > const char* getLastError(); > const char* getDetail(char* detail); > const bool deposit(uint number, double amount); > const bool withdraw(uint number, double amount); > const double getBalance(uint number); > const bool transfer(uint numberFrom, IBank* bankTo, uint numberTo, > double amount); > const bool transferAccept(IBank* bankFrom, uint numberTo, double > amount); > } > > export extern (C) IBank Get(); > ----------------- > > > And the main program in D that uses the DLL: > ----------------- > module main; > > import std.stdio; > import core.runtime; > import core.sys.windows.windows; > import std.string; > import std.conv; > > import ibank; > > int main() > { > alias extern(C) IBank function() getBankInstance; > FARPROC pDllFunctionVBank, pDllFunctionSberbank; > > // Load DLL file > void* handleVBank = Runtime.loadLibrary("vbank.dll"); > void* handleSberbank = Runtime.loadLibrary("sberbank.dll"); > > if ( (handleVBank is null) || (handleSberbank is null) ) > { > writeln("Couldn't find necessary DLL files"); > return 1; > } > > getBankInstance get1 = cast(getBankInstance) > GetProcAddress(handleVBank, "Get".toStringz); > getBankInstance get2 = cast(getBankInstance) > GetProcAddress(handleSberbank, "Get".toStringz); > > if ( get1 is null || get2 is null ) > { > writeln("Couldn't load factory functions"); > return 2; > } > > getBankInstance get; > IBank vbank = (*get1)(); > IBank sberbank = get2(); > > > uint sbnum = 100500; > uint vbnum = 128500; > > writeln("You have an account in Sberbank (100500)"); > auto balance = sberbank.getBalance(sbnum); > writefln("getBalance(%d) = %s", sbnum, balance); > bool res = sberbank.withdraw(sbnum, 500.0); > writefln("withdraw(%d, %f) = %s", sbnum, 500.0, res); > writeln("You got it!"); > ... > ----------------- > > The output I get is (in case I use extern (Windows, C or Pascal)): > ----------------- > You have an account in Sberbank (100500) > getBalance(100500) = -nan > got into GenericBank::getBalance() // this is an output from a method > called inside the DLL > account number = 100500 // inside the DLL > balance is 1100 // inside the DLL > withdraw(100500, 500.000000) = false > You got it! > ----------------- First, to interact with C++ `interface` you need: --- extern(C++) interface Ixxx { ... } --- Your `IBank` C++ functions are declared as `APIENTRY` which is almost definitely defined as `__stdcall`. So the correct interface declaration is: --- extern(C++) interface IBank { extern(Windows) const char* getLastError(); ... } --- As all your functions are `APIENTRY`, write `extern(Windows):` before them. And use `c_ulong` as analogue of `unsigned long`. So full correct `IBank` interface declaration here: --- import core.stdc.config: c_ulong; extern(C++) interface IBank { extern(Windows): const char* getLastError(); const char* getDetail(char* detail); bool deposit(c_ulong number, double amount); bool withdraw(c_ulong number, double amount); double getBalance(c_ulong number); bool transfer(c_ulong numberFrom, IBank* bankTo, c_ulong numberTo, double amount); bool transferAccept(IBank* bankFrom, c_ulong numberTo, double amount); }; --- -- Денис В. Шеломовский Denis V. Shelomovskij |
October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Denis Shelomovskij | On Monday, 29 October 2012 at 12:11:11 UTC, Denis Shelomovskij wrote:
> const char* getLastError();
> const char* getDetail(char* detail);
These return values should be const(char)* and the method shouldn't be const.
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October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Jakob Ovrum | 29.10.2012 16:40, Jakob Ovrum пишет: > On Monday, 29 October 2012 at 12:11:11 UTC, Denis Shelomovskij wrote: >> const char* getLastError(); >> const char* getDetail(char* detail); > > These return values should be const(char)* and the method shouldn't be > const. > Sorry, my bad. -- Денис В. Шеломовский Denis V. Shelomovskij |
October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Denis Shelomovskij | >
> As all your functions are `APIENTRY`, write `extern(Windows):` before them. And use `c_ulong` as analogue of `unsigned long`. So full correct `IBank` interface declaration here:
> ---
> import core.stdc.config: c_ulong;
>
> extern(C++) interface IBank
> {
> extern(Windows):
> const char* getLastError();
> const char* getDetail(char* detail);
> bool deposit(c_ulong number, double amount);
> bool withdraw(c_ulong number, double amount);
> double getBalance(c_ulong number);
> bool transfer(c_ulong numberFrom, IBank* bankTo, c_ulong numberTo, double amount);
> bool transferAccept(IBank* bankFrom, c_ulong numberTo, double amount);
> };
> ---
Thank you very much, Denis. It was quite confusing to mix extern(C++) and extern(Windows). And I also thank Jakob for syntax specification.
BTW, it's said in the ABI reference that `unsigned long` must be substituted with `uint`. And it seems to work fine for the data I used in the example.
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October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Artie | "Artie" <apple2000@mail.ru> wrote in message news:uhdpnavdyokxigczlxto@forum.dlang.org... > > BTW, it's said in the ABI reference that `unsigned long` must be substituted with `uint`. And it seems to work fine for the data I used in the example. unsigned int and unsigned long are the same size in 32 bit C/C++, but are mangled differently when using C++ name mangling. unsigned long may not be 32 bits on all platforms, so to portably match the size used by the native C/C++ compiler you should use the c_ulong aliases. The problem with name mangling is avoided in this case as you're not using C++ name mangling, you're using stdcall name mangling, which only keeps track of argument sizes, not their types. |
October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Artie Attachments:
| It will be fine for Windows, because in Window long and unsigned long are always 4 byte. But other systems (for instance, all Linux distros) have long and unsigned long 8 bytes under 64-bit systems. c_ulong makes sure, that it's the correct size on all systems. On Mon, Oct 29, 2012 at 5:55 PM, Artie <apple2000@mail.ru> wrote: > >> As all your functions are `APIENTRY`, write `extern(Windows):` before them. And use `c_ulong` as analogue of `unsigned long`. So full correct `IBank` interface declaration here: >> --- >> import core.stdc.config: c_ulong; >> >> extern(C++) interface IBank >> { >> extern(Windows): >> const char* getLastError(); >> const char* getDetail(char* detail); >> bool deposit(c_ulong number, double amount); >> bool withdraw(c_ulong number, double amount); >> double getBalance(c_ulong number); >> bool transfer(c_ulong numberFrom, IBank* bankTo, c_ulong numberTo, >> double amount); >> bool transferAccept(IBank* bankFrom, c_ulong numberTo, double amount); >> }; >> --- >> > > Thank you very much, Denis. It was quite confusing to mix extern(C++) and > extern(Windows). And I also thank Jakob for syntax specification. > > BTW, it's said in the ABI reference that `unsigned long` must be substituted with `uint`. And it seems to work fine for the data I used in the example. > -- Bye, Gor Gyolchanyan. |
October 29, 2012 Re: Can't use a C++ class from a DLL | ||||
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Posted in reply to Daniel Murphy | On Monday, 29 October 2012 at 14:01:09 UTC, Daniel Murphy wrote:
> "Artie" <apple2000@mail.ru> wrote in message
> news:uhdpnavdyokxigczlxto@forum.dlang.org...
>>
>> BTW, it's said in the ABI reference that `unsigned long` must be substituted with `uint`. And it seems to work fine for the data I used in the example.
>
> unsigned int and unsigned long are the same size in 32 bit C/C++, but are
> mangled differently when using C++ name mangling. unsigned long may not be
> 32 bits on all platforms, so to portably match the size used by the native
> C/C++ compiler you should use the c_ulong aliases.
> The problem with name mangling is avoided in this case as you're not using
> C++ name mangling, you're using stdcall name mangling, which only keeps
> track of argument sizes, not their types.
That makes sense. I was unaware of such details. Thanks a lot.
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