Is there a Haskell equivalent of POSIX' dlopen or Windows' LoadLibrary? All the FFI stuff only seems to work with libraries specified at link time.
A quick hoogling brings up System.Posix.DynamicLinker. You can also try the plugins package for more high-level stuff.
For Windows, there is System.Win32.DLL. The result of getProcAddress can be converted to a function pointer using castPtrToFunPtr.
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I've got the following situation:
Library X is a wrapper over some code in C.
Library A depends on library X.
Library B uses Template Haskell and depends on library A.
GHC bug #9010 makes it impossible to install library B using GHC 7.6. When TH is processed, GHCi fires up and tries to load library X, which fails with a message like
Loading package charsetdetect-ae-1.0 ... linking ... ghc:
~/.cabal/lib/x86_64-linux-ghc-7.6.3/charsetdetect-ae-1.0/
libHScharsetdetect-ae-1.0.a: unknown symbol `_ZTV15nsCharSetProber'
(the actual name of the “unknown symbol” differs from machine to machine).
Are there any workarounds for this problem (apart from “don't use Template Haskell”, of course)? Maybe library X has to be compiled differently, or there's some way to stop it from loading (as it shouldn't be called during code generation anyway)?
This is really one of the main reasons that 7.8 switched to dynamic GHCi by default. Rather than try to support every feature of every object file format, it builds dynamic libraries and lets the system dynamic loader handle them.
Try building with the g++ option -fno-weak. From the g++ man page:
-fno-weak
Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++.
There is another issue with __dso_handle. I found that you can at least get the library to load and apparently work by linking in a file which defines that symbol. I don't know whether this hack will cause anything to go wrong.
So in X.cabal add
if impl(ghc < 7.8)
cc-option: -fno-weak
c-sources: cbits/dso_handle.c
where cbits/dso_handle.c contains
void *__dso_handle;
In Linux, I am getting error "undefined reference to 'pathfind' while linking objects in Makefile. libgen, libposix4 libraries are linked to create executable. These libraries are not present in Linux. This pathfind() function declaration is present in libgen.h in Unix but nowhere in Linux. And am not getting where it is defined in Unix too. I assume that its a library function of libgen or libposix4. Is there any equivalent function in Linux or I need to write my own function to acheive the functionality of pathfind()?? also equivalent libraries for libgen and libposix4?
I have pdflib_py.so library i want to call from haskell. I do not have a header file. And as you can see the lib's name is not in the standard libbla form.
How do i access it from haskell ?
I followed c2hs tutorial. But it requires a header file (which i do not have) and ghc requires a library name to be in libbla format. I could of course rename pdflib_py.so to libpdfpy.so, in fact i tried it (it did not work), but that's silly to assume that you cannot access a library from haskell because of its name. I'm surely missing something here.
You can download the pdflib library from here http://www.pdflib.com/download/pdflib-family/pdflib-8/
They have bundles for c++, java, php, python etc.
Why don't i use c++ library but a python one ? Well, c++ library libbpdf.a requires to be compiled with g++. And haskell does not work with g++, I would have to write a C wrapper first. Luckily someone already did it for me. That's what a pdflib_py.so is - a c wrapper over libpdf library.
So, how do i use a library with non standard name and no header file from haskell ?
I dont think your approach is correct. You should compile pdflib with g++ into a shared library and then link against it. The C++ library they provide already uses "extern C" wrapper so the symbols exported will be excatly as you would expect them to be.
To sum up, I propose the following solution:
Download C++ bundle
Compile with g++ to make shared .so library
Use header .h file from bundle to make Haskell bindings
Link Haskell code against .so library
I have a game which uses std::wstring as its basic string type in thousand of places as well as doing operations with wchar_t and its functions: wcsicmp() wcslen() vsprintf(), etc.
The problem is wstring is not supported in R5c (latest ndk at the time of this writting).
I can't change the code to use std::string because of internationalization and I would be breaking the game engine which is used by many games ...
Which options do I have?
1 - Replace string and wstring with my own string classes
This would give me better platform independency, but it is ridiculous to reimplement the wheel.
I've already started with a COW implementation of strings. I need it to be COW because I use them as keys in hash_maps.
This is of course lots of work and error prone ... but it seems it is something I can do.
2 - Try to fix the NDK recompiling the STLPort with my own implementations of the wide char string functions of the C standart library (wcslen, mbstowcs ... )
This would be the preferable way ... but I have no idea how to do it :(
How do I replace a function (lets say wcslen) in the libstdc++.a or libstlport_static.a? (not sure where they are :()
And as well I'm not sure which functions I need to reimplement, I know wcslen is not working so I guess they should be all ...
3 - Do you have any other idea?
I can't wait for an official fix for this and I will have to go with option #1 if I can't realize how to do #2.
I've read somewhere that if you target 2.3 you can use wstrings, but I ought to target Android 2.1.
PS: Forgot to say I need to use STL of course, but no RTTI and I can live without exceptions.
Thanks in advance!
Try out CrystaX's NDK. It has had stl support long before the official google one. The current version (r5), which is based off the of the official ndk r5, is still beta 3, but it does have wchar_t support.
http://www.crystax.net/android/ndk-r5.php
I'm suffering from the same problem as you, but my only other thought is to load the strings via the JNI (as jstring* in native land), then convert them to UTF characters as necessary. Take a look at the available JNI string functions here:
http://download.oracle.com/javase/1.5.0/docs/guide/jni/spec/functions.html#string_operations
Qt provides an excellent copy-on-write, international-friendly string implementation, QString, that is LGPLed.
You could, in theory extract it from the Qt source and use it in your own project. You will find the QString implementation in src/corelib/tools/qstring.h and .cpp in a Qt source download. You would also need the QChar, QByteArray, QAtomic, and QNamespace includes/classes (all under the corelib folder,) and you should define QT_NO_STL_WCHAR when compiling. (For this I would compile by hand or using my own script/Makefile.) Not simple, but once you get it up and running your life will be a lot simpler. It's better than reinventing the wheel, because it comes with loads of convenience functions and features.
Rather than stripping out just QString, you could also just use the QtCore module as a whole. See the android-lighthouse project for a Qt port to Android. (Also, it might be better to get your sources from there than from the above "vanilla" link, regardless of what you do.)
I'm trying to test out a library that provides a VC++ example; however, I use gcc/g++ for all of my projects.
Well, the way the VC++ example accesses the library is it uses the #import directive, passing the location of the library DLL, then it does a using namespace LIBRARYNAME, and then it's able to create some undefined type (I'd assume it's defined in the DLL) and create a new instance of it with __uuidof. From then on, to call one of the library functions the example just does a createdObj->foo() and that's that.
Well... g++'s #import is different from VC++'s import (see here), so this example won't work for me.
Is there any way this can be converted to compile under g++, or am I SOL until the library developer provides me with a static library I can try out?
If you are using cygwin, then this page: http://www.cygwin.com/cygwin-ug-net/dll.html will provide you with all the help you need.
If you are using mingw, you can accomplish the same thing, but you probably won't have grep and sed, so you'll have to use some other method of doing the filtering to get your .def file.
If you were using #import in VC++ it means the DLL isn't a regular DLL, it's a COM DLL.
Since gcc doesn't have COM support, you'll just have to wait for the library author to write a non-COM version.
Maybe it could have helped you to use the OLEViewer and "View type information" to extract the basics of the IDL. Or maybe you could just use the VC++ generated .tlh and .tli files and import them into your G++ project.
I guess this answer is way too late, but right now I'm encountering similar issues myself so I just got into this thread. Hope you found the solution on time.
Regards.