C++ and Go 1.2

[Dorival Pedroso]

Hi, I've heard Go 1.2 (CGO) supports C++ now... Is there any example/doc on how to link a C++ library the way? Cheers. Dorival

[Ian Lance Taylor]

The cgo program doesn't really support C++. It will work for straight
functions in C++, but not for methods.

You can use SWIG to interface with C++ code.

Ian

[Stephen Gutekanst]

I too am interested in what sort of things CGO can do when interacting with C++.

(For those curious, revision is here: https://code.google.com/p/go/source/detail?r=24596e5bca7d)

What level of interaction can be done with C++ classes and OO model?

Stephen

[Stephen Gutekanst]

It seems me and Ian mailed at nearly the same time.

Ian's response answers my questions fully.

Stephen

[Dorival Pedroso]

thanks a lot for the reply.

the wrapping code i'm creating involves only straight functions in C++

nonetheless, i'm struggling with linkage problems (small code attached)

cheers.

d

[Sebastien Binet]

Dorival,

connectmpi.h needs to read:

#ifndef CONNECTMPI_H
#define CONNECTMPI_H

#ifdef __cplusplus
extern "C" {
#endif

void startmpi(int debug);
void stopmpi(int debug);

#ifdef __cplusplus
} /* extern "C" */
#endif

#endif // CONNECTMPI_H


-s

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[Dorival Pedroso]

here it goes a very small example using boost...

if i learn how to link this i'll probably be able to fix the mpi example as well

i'm compiling and running with:

g++ `go env GOGCCFLAGS` -shared -o libexcpp.so cpplib.cpp

go build main.go

the problem with the other mpi test is:

    mpic++ `go env GOGCCFLAGS` -shared -o libconnectmpi.so connectmpi.cpp

    go build main.go

/usr/bin/ld: $WORK/mpi/_obj/connectmpi.cpp.o: undefined reference to symbol '_ZN3MPI8Datatype4FreeEv'

/usr/lib/libmpi_cxx.so.1: error adding symbols: DSO missing from command line

collect2: error: ld returned 1 exit status

many thanks in advance!

cheers

[Sebastien Binet]

Dorival,

On Mon, Aug 26, 2013 at 8:39 AM, Dorival Pedroso <dorival...@gmail.com> wrote:

thanks a lot; but after changed as suggested i still have the same problems

i'm compiling with:

mpic++ `go env GOGCCFLAGS` -shared -o libconnectmpi.so connectmpi.cpp

and building with:

go build main.go

the errors are:

/usr/bin/ld: $WORK/mpi/_obj/connectmpi.cpp.o: undefined reference to symbol '_ZN3MPI8Datatype4FreeEv'

/usr/lib/libmpi_cxx.so.1: error adding symbols: DSO missing from command line

collect2: error: ld returned 1 exit status

I'll try another example that doesn't involve MPI to see how it goes

the following worked for me:

$ cat mpi.go

 package mpi

/*

#cgo CFLAGS: -O3 -I. -I/usr/include/mpi

#cgo LDFLAGS: -L/usr/lib/openmpi -lmpi -lmpi_cxx -lstdc++

#include "connectmpi.h"

*/

import "C"

// Start initialises MPI

func Start(debug bool) {

if debug {

C.startmpi(1)

} else {

C.startmpi(0)

}

}

// Stop finalises MPI

func Stop(debug bool) {

if debug {

C.stopmpi(1)

} else {

C.stopmpi(0)

}

}

$ cat 

$ go get .

$ go run main.go

startmpi: hi from 0. debug = 1

stopmpi: goodbye from 0. debug = 1

that's the whole point of the CL mentionned earlier in this thread: don't require a Makefile for compiling cxx files which expose a C-API and have those file blend seamlessly into the "go get" machinery.

-s

cheers.

d

--

Dr Dorival Pedroso MSc PhD Brisbane Australia +61 0420411142 http://www.cpmech.com Lecturer School of Civil Engineering The University of Queensland

[Dorival Pedroso]

thanks a lot Sebastien.

the method fixed my problem as well and the idea is quite interesting: avoiding an intermediary .so file...

just another quick question: is it possible to include something like:

`mpic++ -showme:link`

into the .go file?

ps: i'll post the fix with the boost test soon as well

cheers

d

[Sebastien Binet]

On Mon, Aug 26, 2013 at 10:01 AM, Dorival Pedroso <dorival...@gmail.com> wrote:

thanks a lot Sebastien.

the method fixed my problem as well and the idea is quite interesting: avoiding an intermediary .so file...

just another quick question: is it possible to include something like:

`mpic++ -showme:link`

into the .go file?

nope.

although, if you can somehow translate this information into a pkg-config file, then you're golden.

(as go-get can be instructed to use pkg-config files to automatically configure the build)

-s

[Gerard]

I bet the answer is yes, but is this documented somewhere?

[mobiled...@gmail.com]

This thread can be useful:

gccgo + c++ library as a Golang package
https://groups.google.com/forum/#!searchin/golang-nuts/service/golang-nuts/0PtkEbR-Y7k/yjshat2uJ7IJ

On Sunday, August 25, 2013 9:37:35 PM UTC-7, Dorival Pedroso wrote:

[Dorival Pedroso]

Thanks for the help, everyone!

For reference, I'm posting an example using boost:

files structure:

$GOPATH/src

     /excpp

          cpplib.cpp

          cpplib.h

          golib.go

     /use_excpp

          main.go

cpplib.cpp

#include <string>

#include <iostream>

#include <boost/algorithm/searching/boyer_moore.hpp>

extern "C" {

void runalgo() {

    namespace ba = boost::algorithm;

    std::string haystack("ABACAB is it everywhere!");

    std::string needle1 ("ACAB");

    std::string needle2 ("not ABA");

    if (ba::boyer_moore_search(haystack.begin(), haystack.end(), needle1.begin(), needle1.end()) != haystack.end ()) {

        std::cout << "Found '" << needle1 << "'  in '" << haystack << "' (boyer-moore 1)" << std::endl;

    } else {

        std::cout << "Did NOT find '" << needle1 << "'  in '" << haystack << "' (boyer-moore 1)" << std::endl;

    }

}

} // extern "C"

cpplib.h

#ifndef CPPLIB_H 

  #define CPPLIB_H 

  #ifdef __cplusplus 

  extern "C" { 

  #endif 

  void runalgo();

  #ifdef __cplusplus 

  }

  #endif 

#endif

golib.go

package excpp

/*

#cgo LDFLAGS: -lstdc++

#include "cpplib.h"

*/

import "C"

// GoRunAlgo

func GoRunAlgo() {

    C.runalgo()

}

main.go

package main

import (

    "excpp"

)

func main() {

    excpp.GoRunAlgo()

}

to run only (and not install):

  go build main.go

with:

  go install 

from the excpp directory,  we get a static library named excpp.a in $GOPATH/pkg/...

nm excpp.a

nm: __.GOSYMDEF: File format not recognized

nm: __.PKGDEF: File format not recognized

nm: _go_.6: File format not recognized

nm: _cgo_import.6: File format not recognized

nm: _cgo_defun.6: File format not recognized

_all.o:

                 U __assert_fail

0000000000000000 T _cgo_cb939bbdcaaf_Cfunc_runalgo

                 U __cxa_atexit

                 U __dso_handle

0000000000000000 V DW.ref.__gxx_personality_v0

                 U _GLOBAL_OFFSET_TABLE_

0000000000000000 t _GLOBAL__sub_I_cpplib.cpp

                 U __gxx_personality_v0

0000000000000000 r .LC0

0000000000000000 r .LC1

0000000000000074 r .LC10

0000000000000018 r .LC2

0000000000000022 r .LC3

000000000000002c r .LC4

0000000000000045 r .LC5

000000000000004a r .LC6

0000000000000052 r .LC7

000000000000005a r .LC8

0000000000000062 r .LC9

                 U memset

                 w __pthread_key_create

0000000000000010 T runalgo

                 U _Unwind_Resume

                 U _ZdlPv

0000000000000000 W _ZN5boost9algorithm18boyer_moore_searchIN9__gnu_cxx17__normal_iteratorIPcSsEES5_EET0_S6_S6_T_S7_

                 U _ZNKSt5ctypeIcE13_M_widen_initEv

                 U _ZNSo3putEc

                 U _ZNSo5flushEv

                 U _ZNSs12_M_leak_hardEv

                 U _ZNSs4_Rep10_M_destroyERKSaIcE

                 U _ZNSs4_Rep10_M_disposeERKSaIcE

                 U _ZNSs4_Rep20_S_empty_rep_storageE

                 U _ZNSsC1EPKcRKSaIcE

                 U _ZNSt8ios_base4InitC1Ev

                 U _ZNSt8ios_base4InitD1Ev

                 U _ZNSt9basic_iosIcSt11char_traitsIcEE5clearESt12_Ios_Iostate

                 U _Znwm

                 U _ZSt16__ostream_insertIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_PKS3_l

                 U _ZSt16__throw_bad_castv

                 U _ZSt17__throw_bad_allocv

                 U _ZSt4cout

0000000000000000 b _ZStL8__ioinit

0000000000000000 t _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc.part.2

0000000000000000 r _ZZN5boost9algorithm11boyer_mooreIN9__gnu_cxx17__normal_iteratorIPcSsEENS0_6detail9BM_traitsIS5_EEE17compute_bm_prefixINS3_IS4_St6vectorIcSaIcEEEESB_IlSaIlEEEEvT_SH_RT0_E19__PRETTY_FUNCTION__

00000000000001c0 r _ZZN5boost9algorithm11boyer_mooreIN9__gnu_cxx17__normal_iteratorIPcSsEENS0_6detail9BM_traitsIS5_EEE17compute_bm_prefixIS5_St6vectorIlSaIlEEEEvT_SE_RT0_E19__PRETTY_FUNCTION__

So, apparently all boost functions are (statically) in excpp.a?

Cheers,

Dorival

[Bonly H]

I want to know about support of c++ in go 1.2  version too..

在 2013年8月27日星期二UTC+8上午9时55分52秒，Dorival Pedroso写道：

[Andrew Gerrand]

On 2 December 2013 00:57, Bonly H <h.b...@gmail.com> wrote:

I want to know about support of c++ in go 1.2  version too..

http://golang.org/doc/go1.2#cgo_and_cpp