Linking cgo with Visual Studio x64 release libraries on Windows

[adi.4...@gmail.com]

I'm trying to link a Go program with a C function from a dll compiled in Visual Studio (x64) on Windows.

The C++ code is this:

extern "C" {

__declspec(dllexport) int add(int a, int b) {

return a+b;

}

};

The Go code is:

package main

/*

__declspec(dllimport) int add(int,int);

#cgo LDFLAGS: cproj.lib

*/

import "C"

import "fmt"

func main() {

        a := C.int(3)

        b := C.int(4)

        c := C.add(a,b)

        d := uint32(c);

        fmt.Printf("a+b = %v\n", d)

}

I put the .lib and .dll files generated by Visual Studio, next to the .go file.

But when I build using the command

go build cgo_example.go

I get the following output:

# command-line-arguments

cproj.lib: error adding symbols: File format not recognized

collect2.exe: error: ld returned 1 exit status

I must be doing something wrong.

Any ideas what it is?

[andrewc...@gmail.com]

I could be wrong, but I thought cgo on windows required a mingw based c compiler.

[chai2010]

You need generate x.a for cgo link.

1. create cproj.def file:

```

LIBRARY cproj.dll

EXPORTS

add

```

2. generate libcproj.a

```

dlltool -dllname cproj.dll --def cproj.def --output-lib libcproj.a

```

3. cgo link libcproj.a

```

#cgo LDFLAGS: -L. -lcproj

```

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https://github.com/chai2010

[Doug Henderson]

HI,

I believe there are (at least) a couple of steps needed to allow you to use 3rd party supplied or self created windows libraries.

The loader does not like the format of a <x>.lib file.

"gendef" compiled for your version of mingw64 creates  <x>.def file from a <x>.lib

"dlltool" for your version of mingw64 creates a lib<x>.a file from a <x>.dll file and the <x>.def file

The loader likes the format of the <x>.a file. This means, I think, that the <x>.dll has been ripped apart to create the <x>.a file.

I found the documentation for cgo to be a bit like an onion. You have to keep peeling back layers until you get to the detailed answers.

Best of luck, and please report back on how you did it, or I may be asking the same question later!

Doug

On 20 April 2015 at 19:33, <andrewc...@gmail.com> wrote:

I could be wrong, but I thought cgo on windows required a mingw based c compiler.

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[Adi Levin]

It worked like a charm! I just followed chai2010's instructions, and there was no problem. Thank you!