undefined reference to c function when calling from go code

Question

Im trying to call a simple c function from within go with cgo

The files are as follows:

goFile.go:

package main

//#include "cFile.h"
import "C"

func main() {
    C.printInC()
}

cFile.h:

void printInC();

cFile.c:

#include "cFile.h"
#include <stdio.h>

void printInC(){
    printf("Test");
}

running go build goFile.go throws the following exception:

C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: $WORK\b001\_x002.o: in function `_cgo_f9774dcf54b4_Cfunc_printInC':
/tmp/go-build/cgo-gcc-prolog:49: undefined reference to `printInC'
collect2.exe: error: ld returned 1 exit status

I'm not really sure why this isn't working, I've looked at multiple tutorials for cgo that implement calling c functions exactly the same way without a problem.

I am not familiar with Go but the important information would be how you tell Go which files to use. How do you tell Go to include the C code? Where did you tell Go to include cFile.c? — Gerhardh
– Gerhardh, Commented Apr 23, 2020 at 11:55
@Gerhardh: Through comments above import "C". The compiler flags and linking information may also be mentioned if required. — Azeem
– Azeem, Commented Apr 23, 2020 at 11:57
There is only a comment for the header. No implementation included there. — Gerhardh
– Gerhardh, Commented Apr 23, 2020 at 12:00
@Gerhardh: The implementation is in .c file which is automatically referenced. It's just like C and C++ where the header file is included. But, you may also write your C or C++ code e.g. functions in the comments and reference those later in Go code. Here's an example. — Azeem
– Azeem, Commented Apr 23, 2020 at 12:10
In C you must include the C file to get the implementation. A header only provides declarations without implementation. If you only include the header, you will get the same "undefined reference" error. According to your answer it seems to work now if you just include everything from the folder. — Gerhardh
– Gerhardh, Commented Apr 23, 2020 at 12:13

Painkiller · Accepted Answer · 2020-04-23 11:58:14Z

3

I've found the problem.

When running go build goFile.go the go tool apparently only builds goFile.go, when i run go build on the entire directory everything works fine..

answered Apr 23, 2020 at 11:58

Painkiller

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1 Comment

Azeem Over a year ago

go build <filename.go> may work if all the required code is included in that file. See this example.

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