How to compile and call a CXX-static library in Golang

touch some files first

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# create a directory for this project
mkdir -p ./hi/lib; cd ./hi
touch ./main.go ./lib/hi.h ./lib/hi.cpp

Create a header file: hi.h

In comparison with c-static-lib, the header file here has some extra contents

extern “C” { … }

mainly to be compatible with C++ compilers.

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#ifndef HI_H
#define HI_H

#ifdef __cplusplus
extern "C" {
#endif

void print_hi();

#ifdef __cplusplus
}
#endif

#endif // HI_H

Create a source file: hi.cpp

Different from c-static-lib, the c++ source file must include the header file.

#include “hi.h”

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#include <iostream>
#include "hi.h"

void print_hi() {
    std::cout << "hi, from C++\n";
}

Create a main file: main.go

Compared to c-static-lib, the LDFLAGS here has an extra -l stdc++ to link the C++ standard library.

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package main

/*
#cgo CFLAGS: -I ${SRCDIR}/lib
#cgo LDFLAGS: -L ${SRCDIR}/lib -l hi -l stdc++
#include "hi.h"
*/
import "C"

func main() {
    C.print_hi()
}

Compile the source file into a static library

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g++ -c ./lib/hi.cpp -o ./lib/hi.o
ar rcs ./lib/libhi.a ./lib/hi.o

Run

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# go run directly
go run main.go

# or build and run
go build -o bin/hi main.go && ./bin/hi

Summary

The key points are different from call c-static-lib:

• use extern "C" { ... } in header file to be compatible with C++ compilers
• source file must include the header file
• add -l stdc++ to LDFLAGS
• use g++ to compile the source file into a static library

If you are not sure the static lib is c or c++, your golang code can always use the c++ way to call it, which is more compatible.

Always add -l stdc++ to LDFLAGS

FYI

Source Code