Building a dynamic library with haskell and using it from C++ - c++

I want to build a dynamic library containing haskell functions. I work on linux and want to call this dynamic library from C++ code.
I used the example at http://wiki.python.org/moin/PythonVsHaskell and have the following files:
Test.hs:
{-# LANGUAGE ForeignFunctionInterface #-}
module Test where
import Foreign.C.Types
hsfun :: CInt -> IO CInt
hsfun x = do
putStrLn "Hello World"
return (42 + x)
foreign export ccall
hsfun :: CInt -> IO CInt
module_init.c:
#define CAT(a,b) XCAT(a,b)
#define XCAT(a,b) a ## b
#define STR(a) XSTR(a)
#define XSTR(a) #a
#include <HsFFI.h>
extern void CAT (__stginit_, MODULE) (void);
static void library_init (void) __attribute__ ((constructor));
static void
library_init (void)
{
/* This seems to be a no-op, but it makes the GHCRTS envvar work. */
static char *argv[] = { STR (MODULE) ".so", 0 }, **argv_ = argv;
static int argc = 1;
hs_init (&argc, &argv_);
hs_add_root (CAT (__stginit_, MODULE));
}
static void library_exit (void) __attribute__ ((destructor));
static void
library_exit (void)
{
hs_exit ();
}
Now I compile this files to a dynamic library:
$ ghc -dynamic -shared -fPIC -optc '-DMODULE=Test' Test.hs module_init.c -o libTest.so
[1 of 1] Compiling Test ( Test.hs, Test.o )
Linking libTest.so ...
This creates among other things the file Test_stub.h:
#include "HsFFI.h"
#ifdef __cplusplus
extern "C" {
#endif
extern HsInt32 hsfun(HsInt32 a1);
#ifdef __cplusplus
}
#endif
and Test_stub.c:
#define IN_STG_CODE 0
#include "Rts.h"
#include "Stg.h"
#ifdef __cplusplus
extern "C" {
#endif
extern StgClosure Test_zdfhsfunzua165_closure;
HsInt32 hsfun(HsInt32 a1)
{
Capability *cap;
HaskellObj ret;
HsInt32 cret;
cap = rts_lock();
cap=rts_evalIO(cap,rts_apply(cap,(HaskellObj)runIO_closure,rts_apply(cap,&Test_zdfhsfunzua165_closure,rts_mkInt32(cap,a1))) ,&ret);
rts_checkSchedStatus("hsfun",cap);
cret=rts_getInt32(ret);
rts_unlock(cap);
return cret;
}
static void stginit_export_Test_zdfhsfunzua165() __attribute__((constructor));
static void stginit_export_Test_zdfhsfunzua165()
{getStablePtr((StgPtr) &Test_zdfhsfunzua165_closure);}
#ifdef __cplusplus
}
#endif
Then I create a cpp file main.cpp:
#include "Test_stub.h"
#include <iostream>
using namespace std;
int main()
{
cout << hsfun(5);
}
and want to compile and link it. But when I call g++, it says:
$ g++ -I/usr/lib/ghc-7.0.3/include -L. -lTest main.cpp
/tmp/ccFP2AuB.o: In function `main':
main.cpp:(.text+0xa): undefined reference to `hsfun'
collect2: ld gab 1 als Ende-Status zurück
So I added the Test_stub.o file to the command line (although I think the hsfun function should already be defined in libTest.so which is added via the -lTest parameter. I don't think, I should link the Test_stub.o file into the executable because I want to use dynamic linking), but this also doesn't work:
$ g++ -I/usr/lib/ghc-7.0.3/include -L. -lTest main.cpp Test_stub.o
Test_stub.o: In function `hsfun':
Test_stub.c:(.text+0x9): undefined reference to `rts_lock'
Test_stub.c:(.text+0x16): undefined reference to `rts_mkInt32'
Test_stub.c:(.text+0x1d): undefined reference to `Test_zdfhsfunzua165_closure'
Test_stub.c:(.text+0x28): undefined reference to `rts_apply'
Test_stub.c:(.text+0x2f): undefined reference to `base_GHCziTopHandler_runIO_closure'
Test_stub.c:(.text+0x3a): undefined reference to `rts_apply'
Test_stub.c:(.text+0x4a): undefined reference to `rts_evalIO'
Test_stub.c:(.text+0x5c): undefined reference to `rts_checkSchedStatus'
Test_stub.c:(.text+0x66): undefined reference to `rts_getInt32'
Test_stub.c:(.text+0x70): undefined reference to `rts_unlock'
Test_stub.o: In function `stginit_export_Test_zdfhsfunzua165':
Test_stub.c:(.text.startup+0x3): undefined reference to `Test_zdfhsfunzua165_closure'
Test_stub.c:(.text.startup+0x8): undefined reference to `getStablePtr'
collect2: ld gab 1 als Ende-Status zurück
Do I have to link the Test_stub.o? If yes, why? And which arguments should I pass to the linker?

Probably easier than wrestling with g++ is letting ghc do the work,
ghc main.cpp -o hithere -L. -lTest -lstdc++
did the job for me after creating the shared lib the way you did. I have tested it with 7.2.2 and 7.0.2, both worked here.

Related

Cannot Call C++ Code from C without Error [duplicate]

This question already has answers here:
How to mix C++ and C correctly
(2 answers)
Closed 4 years ago.
I'm trying to write a C++ library that can be called from C. However, whenever I try to even write a bare minimum example, it crashes with undefined references. Here is my code:
mylibrary.h
#ifndef __MY_CPP_THING_H
#define __MY_CPP_THING_H
#ifdef __cplusplus
extern "C" {
#endif
void printSomething();
#ifdef __cplusplus
}
#endif
#endif
mylibrary.cpp
#include <iostream>
#include "mylibrary.h"
extern "C" {
void printSomething() {
std::cout << "PLEASE PRINT\n";
}
}
main.c
#include "mylibrary.h"
int main() {
printSomething();
return 0;
}
The compiling process goes something like this:
g++ -c mylibrary.cpp -o mylibrary.o (create "mylibrary.o")
ar rcs libmylibrary.a mylibrary.o (create static library "libmylibrary.a")
gcc main.c -L. -lmylibrary (link static library and compile C source file)
However, I receive this error dump:
mylibrary.o:mylibrary.cpp:(.text+0x17): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
mylibrary.o:mylibrary.cpp:(.text+0x32): undefined reference to `std::ios_base::Init::~Init()'
mylibrary.o:mylibrary.cpp:(.text+0x62): undefined reference to `std::ios_base::Init::Init()'
mylibrary.o:mylibrary.cpp:(.rdata$.refptr._ZSt4cout[.refptr._ZSt4cout]+0x0): undefined reference to `std::cout'
collect2.exe: error: ld returned 1 exit status
Any suggestions on how to resolve the error?
mylibrary.o still depends on C++ standard library and gcc doesn't know about it. Call gcc with -lstdc++ in the last step.
Creating a dynamic library instead of a static library should do the trick :
$ gcc -c main.c
$ g++ -fPIC -shared -o mylibrary.so mylibrary.cpp
$ gcc -o main main.o mylibrary.so
and then :
$ LD_LIBRARY_PATH=".:${LD_LIBRARY_PATH}" ./main
PLEASE PRINT
with :
$ objdump -p main | grep NEEDED
NEEDED mylibrary.so
NEEDED libc.so.6
$ objdump -p mylibrary.so | grep NEEDED
NEEDED libstdc++.so.6
NEEDED libc.so.6

undefined reference to function in gcc

I am trying to use a C static library but getting the following error while compiling/linking in gcc. The main file test.c needs to call a function from the static library libtest.a
Header file : testcplusplus.h
void print_cplusplus(int b);
testcplusplus.c :
#include <stdio.h>
#include "testcplusplus.h"
void print_cplusplus(int b) {
printf ("Value of b is %d \n",b);
}
Main C file : test.c
#include <stdio.h>
#include "testcplusplus.h"
int main() {
int a = 2 ;
print_cplusplus(a);
}
Commands Used :
g++ -c -o testcplusplus.o testcplusplus.c
ar rvs libtest.a testcplusplus.o
gcc -o test test.c -L. -ltest **// Error comes here**
Error:
In function `main':
test.c:(.text+0x15): undefined reference to `print_cplusplus'
collect2: ld returned 1 exit status
You only specify function parameter types when you declare/define the function, not when you call it. The function call should look like
print_cplusplus(a);
You also need to include testcplusplus.h from test.c so that the declaration is available when you call it. The return type of main needs to be int; and print_cplusplus should either have void return type, or should return a value.
Finally, you'll need to declare the function extern "C" for it to be callable from a C program - but only when compiling C++.
// testcplusplus.h
#ifdef __cplusplus
extern "C" {
#endif
void print_cplusplus(int b);
#ifdef __cplusplus
}
#endif
You don't rewrite a variables type when you use it, it's only used in declarations:
print_cplusplus(a);

g++ linking against static library [duplicate]

This question already has answers here:
"undefined reference" when linking against a static library
(4 answers)
Closed 8 years ago.
my main.cpp:
#include <iostream>
int foo(int arg);
using namespace std;
int main()
{
int x = foo(22);
cout << x;
return 0;
}
compile command line (Ubuntu 13.10):
g++-4.8 -L. -lfoo main.cpp -o main_app
libfoo.a contains int foo(int)
but I always get the same compiler error:
/tmp/cciAyTSP.o: In function `main':
main.cpp:(.text+0x19): undefined reference to `foo(int)'
collect2: error: ld returned 1 exit status
Of course it's impossible to be sure without a reproducible case, but a common error is that if the function foo is written in C then you need to put
extern "C" { int foo(int); }
in the .h file for the C++ program to let it know that the function was not written in C++.
To write a cross-language header file that will be good for both C and C++ the common approach is
#ifdef __cplusplus
extern "C" {
#endif
... C declarations ...
#ifdef __cplusplus
}
#endif
In addition to 6502's answer and Xephon's suggestion, also be aware that the order of the options matter. Instead of:
g++-4.8 -L. -lfoo main.cpp -o main_app
You should write:
g++-4.8 main.cpp -o main_app -L. -lfoo
That's because ld is a single pass linker. It won't revisit library libfoo to use a symbol from it for main_app.o.

Using a haskell function from C++: Undefined reference error

I want to call haskell functions out of C++ and did use the tutorial at http://www.haskell.org/ghc/docs/7.0.2/html/users_guide/ffi-ghc.html
So I have a haskell file Foo.hs:
module Foo where
foreign export ccall foo :: Int -> IO Int
foo :: Int -> IO Int
foo n = return (length (f n))
f :: Int -> [Int]
f 0 = []
f n = n:(f (n-1))
and called
ghc Foo.hs
which created a Foo_stub.h:
#include "HsFFI.h"
#ifdef __cplusplus
extern "C" {
#endif
extern HsInt foo(HsInt a1);
#ifdef __cplusplus
}
#endif
a Foo_stub.c:
#define IN_STG_CODE 0
#include "Rts.h"
#include "Stg.h"
#ifdef __cplusplus
extern "C" {
#endif
extern StgClosure Foo_zdffoozualy_closure;
HsInt foo(HsInt a1)
{
Capability *cap;
HaskellObj ret;
HsInt cret;
cap = rts_lock();
cap=rts_evalIO(cap,rts_apply(cap,(HaskellObj)runIO_closure,rts_apply(cap, Foo_zdffoozualy_closure,rts_mkInt(cap,a1))) ,&ret);
rts_checkSchedStatus("foo",cap);
cret=rts_getInt(ret);
rts_unlock(cap);
return cret;
}
static void stginit_export_Foo_zdffoozualy() __attribute__((constructor));
static void stginit_export_Foo_zdffoozualy()
{getStablePtr((StgPtr) &Foo_zdffoozualy_closure);}
#ifdef __cplusplus
}
#endif
It also created a Foo_stub.o file.
I now created a main.cpp file:
#include "Foo_stub.h"
int main()
{
foo(3);
}
and tried to compile it.
Using g++ failed:
$ g++ -I/usr/lib/ghc-7.0.3/include/ main.cpp Foo_stub.o
Foo_stub.o: In function `foo':
Foo_stub.c:(.text+0xa): undefined reference to `rts_lock'
Foo_stub.c:(.text+0x18): undefined reference to `rts_mkInt'
Foo_stub.c:(.text+0x20): undefined reference to `Foo_zdffoozualy_closure'
Foo_stub.c:(.text+0x28): undefined reference to `rts_apply'
Foo_stub.c:(.text+0x30): undefined reference to `base_GHCziTopHandler_runIO_closure'
Foo_stub.c:(.text+0x38): undefined reference to `rts_apply'
Foo_stub.c:(.text+0x48): undefined reference to `rts_evalIO'
Foo_stub.c:(.text+0x58): undefined reference to `rts_checkSchedStatus'
Foo_stub.c:(.text+0x62): undefined reference to `rts_getInt'
Foo_stub.c:(.text+0x6d): undefined reference to `rts_unlock'
Foo_stub.o: In function `stginit_export_Foo_zdffoozualy':
Foo_stub.c:(.text+0x80): undefined reference to `Foo_zdffoozualy_closure'
Foo_stub.c:(.text+0x85): undefined reference to `getStablePtr'
collect2: ld returned status 1
so I tried ghc --make. But this also failed:
$ ghc --make main.cpp Foo_stub.o
cc1plus: Warning: Option »-Wimplicit« is valid for C/ObjC, but not for C++ [activated by default]
Foo_stub.o: In function `foo':
Foo_stub.c:(.text+0x20): undefined reference to `Foo_zdffoozualy_closure'
Foo_stub.o: In function `stginit_export_Foo_zdffoozualy':
Foo_stub.c:(.text+0x80): undefined reference to `Foo_zdffoozualy_closure'
collect2: ld returned status 1
How can I compile it?
Try this:
$ ghc --make -no-hs-main main.cpp Foo.hs
I believe the problem is that GHC thinks the stub object file you're passing in is just another object to be linked normally, but you're not passing the Foo.o file itself, so the stub code has nothing to link to! Passing in the source file directly should solve it. (This is just conjecture based on the documentation and the error you're seeing, I haven't tested it.)
I think you could do separate compilation like this:
$ ghc --make Foo.hs
$ ghc --make -no-hs-main main.cpp Foo.o
but I'm not sure. You might also want to look into building your Haskell code into a shared library, and then linking it to your main program normally with g++.
-no-hs-main is required when your program's entry point isn't the Haskell value Main.main, as described in the documentation you linked.

C++ Undefined Reference (Even with Include)

I cannot get this simple piece of code to compile without including the TestClass.cpp file explicitly in my main.cpp file. What am I doing wrong? Thanks in advance!
Here is the code:
TestClass.h
#ifndef TESTCLASS_H_
#define TESTCLASS_H_
class TestClass
{
public:
static int foo();
};
#endif
TestClass.cpp
#include "TestClass.h"
int TestClass::foo() { return 42; }
main.cpp
#include <iostream>
#include "TestClass.h"
using namespace std;
int main()
{
cout << TestClass::foo() << endl;
return 0;
}
Here is the error:
g++ main.cpp -o main.app
/tmp/ccCjOhpy.o: In function `main':
main.cpp:(.text+0x18e): undefined reference to `TestClass::foo()'
collect2: ld returned 1 exit status
Include TestClass.cpp into the commandline, so the linker can find the function definition:
g++ main.cpp TestClass.cpp -o main.app
Alternatively, compile each to their own object file, then tell the compiler to link them together (it will forward them to the linker)
g++ -c main.cpp -o main.o
g++ -c TestClass.cpp -o TestClass.o
g++ main.o TestClass.o -o main.app
You're not compiling and linking against TestClass.cpp (where the implementation of foo() is). The compiler is thus complaining that your trying to use an undefined function.