Building executable for code with cgo produces link errors

[Nicholas Yue]

Hi,

  I am using Go 1.15 on Ubuntu 18.04

  I am learning about cgo via the following tutorial

        https://golang.org/cmd/cgo/

  I have the following two files which I am able to run via

  go run cgo_main.go

  Knowing that it runs, I'd like to build it into an executable but I get the following errors

```

$ go build .

# example.com/user/cgohello

/tmp/go-build161353644/b001/_x003.o: In function `printf':

/usr/include/x86_64-linux-gnu/bits/stdio2.h:104: multiple definition of `Hello'

/tmp/go-build161353644/b001/_x002.o:/usr/include/x86_64-linux-gnu/bits/stdio2.h:104: first defined here

collect2: error: ld returned 1 exit status

```

```

// cgo_main.go

package main

/*

#include "hello.c"

*/

import "C"

import (

"errors"

"log"

)

func main() {

//Call to void function without params

err := Hello()

if err != nil {

log.Fatal(err)

}

}

//Hello is a C binding to the Hello World "C" program. As a Go user you could

//use now the Hello function transparently without knowing that it is calling

//a C function

func Hello() error {

_, err := C.Hello() //We ignore first result as it is a void function

if err != nil {

return errors.New("error calling Hello function: " + err.Error())

}

return nil

}

```

```

//hello.c

#include <stdio.h>

void Hello(){

printf("Hello world [cgo]\n");

}

```

Cheers

[Ian Lance Taylor]

On Thu, Jan 21, 2021 at 10:21 PM Nicholas Yue <yue.ni...@gmail.com> wrote:
>
> /*
> #include "hello.c"
> */
> import "C"

Doing a #include of "hello.c" is unusual. That is most likely your
problem. The comment before the import "C" is handled as C code. C
code rarely does a #include of a .c file. Normally one does a
#include of a .h file.

Ian