GO with C/CPP

directly using C

You can directly using C in the golang. Just include the headers and the C code at the top.

package main

// #include <stdio.h>
// #include <stdlib.h>
//
// static void myprint(char* s) {
//   printf("%s\n", s);
// }
import "C"
import "unsafe"

func main() {
	cs := C.CString("Hello from stdio")
	C.myprint(cs)
	C.free(unsafe.Pointer(cs))
}

using static library

you should generate the object file with

gcc -o foo.o foo.c compile to object file

ar rcs libfoo.a foo.o archive the object file

to include and load the static library

package main

//#cgo CFLAGS: -I./cheader
//#cgo LDFLAGS: -L${SRCDIR}/clib -lnumber
//
//#include "number.h"
import "C"
import "fmt"

func main() {
	fmt.Println(C.number_add_mod(10, 5, 12))
}

using dynamic library(recommend)

the cgo cannot use the cpp directly must be packaged in a c.

let's start with a cpp-lua example.

the luatest.cpp

#include <iostream>
#ifdef __cplusplus
extern "C" {
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
}
#else
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
#endif
const char *lua_script = R"(
version = '1.0.0'
function add(a, b)
    return a + b;
end
)";
void luaTest(){
    lua_State *L = luaL_newstate();
    if (L == nullptr) {
        //std::cerr << "create state failed!" << std::endl;
        exit(-1);
    }

    if (luaL_dostring(L, lua_script) != 0) {
        //std::cerr << "cannot run lua script!" << std::endl;
        exit(-1);
    }

    // get global variable
    lua_getglobal(L, "version");
    const char *version = lua_tostring(L, -1);
    printf("%s\n",version);
    //std::cout << "version: " << version << std::endl;
    lua_pop(L, 1);

    // call global function
    lua_getglobal(L, "add");
    int a = 100;
    int b = 200;
    lua_pushnumber(L, a);
    lua_pushnumber(L, b);
    if (lua_pcall(L, 2, 1, 0) != 0) {
        //std::cerr << "call func failed, got error: " << lua_tostring(L, -1) << std::endl;
        lua_pop(L, 1);
        exit(-1);
    }

    int sum = lua_tonumber(L, -1);
    lua_pop(L, 1);
    printf("%d\n",sum);

    //std::cout << a << " + " << b << " = " << sum << std::endl;
    lua_close(L);
}

the luatest.h

#ifndef CWITHLUA_LUATEST_H
#define CWITHLUA_LUATEST_H
void luaTest();
#endif //CWITHLUA_LUATEST_H

we must use a bridge or interface to package the cpp code

the bridge.h

#ifdef __cplusplus
extern "C" {
#endif
void LuaTest();
#ifdef __cplusplus
}
#endif

the bridge.c

#include "bridge.h"
#include "luatest.h"
#ifdef __cplusplus
extern "C"{
#endif
void LuaTest(){
    luaTest();
}
#ifdef __cplusplus
}
#endif

complie to dynamic lib

g++ luatest.cpp bridge.c -std=c++14 -L/Users/austinguish/Desktop/backend/CWithLua/lib -llua -I/Users/austinguish/Desktop/backend/CWithLua/include -fPIC -shared -o liblt.so

to compile the lib we need add -L -I flags to tell the compiler where the lua header and liblua are.

the directory must be absolute directory not the relative directory!!!

write go code to use the dynamic library

package main
//#cgo CFLAGS: -I${SRCDIR}/cheader
//#cgo LDFLAGS: -lstdc++ -L${SRCDIR}/clib -llt
//#include "bridge.h"
import "C"

func main() {
	C.LuaTest()
}

go build this go file.

go build gowithdlib.go

and run this prog

./gowithdlib

you 'll get this error:

dyld: Library not loaded: liblt.so

You should change the prog's dynamic lib dir.

On Mac:

check the prog

otool -L gowithdlib
install the correct dir to this prog

install_name_tool -change liblt.so /Users/austinguish/go/src/GoWIthC/clib/liblt.so gowithclib

then run

./gowithdlib
the result
```
➜  GoWIthC ./gowithclib
1.0.0
300
```

austinguish/GowithCPP

GO with C/CPP

directly using C

using static library

using dynamic library(recommend)