error on calling go function from c

Question

New to go here. Tried to call go function from C but suffered some compiling issues

Here is the go script

package main
// #cgo CFLAGS: -Wno-error=implicit-function-declaration
// #include <stdlib.h> 
// #include "wrapper.c"
import "C"
//import "unsafe"
import "fmt"
//import "time"

//export dummy
func dummy() int {
    fmt.Println("hi you");
    return 0
}

func main() {
    C.testc()
}

Here is the wrapper

#include <sys/types.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

extern int dummy();

void testc(){
    dummy();
}

When running it, got error

xyz@xyz-HP:~/learn/go$ go run reader.go 
# command-line-arguments
In file included from $WORK/command-line-arguments/_obj/_cgo_export.c:2:0:
reader.go:30:14: error: conflicting types for ‘dummy’
In file included from reader.go:3:0,
                 from $WORK/command-line-arguments/_obj/_cgo_export.c:2:
./wrapper.c:6:12: note: previous declaration of ‘dummy’ was here
/tmp/go-build528677551/command-line-arguments/_obj/_cgo_export.c:8:7: error: conflicting types for ‘dummy’
In file included from reader.go:3:0,
                 from $WORK/command-line-arguments/_obj/_cgo_export.c:2:
./wrapper.c:6:12: note: previous declaration of ‘dummy’ was here

Not_a_Golfer · Accepted Answer · 2015-04-13 13:25:10Z

1

You don't need to declare dummy in your C file. Here's how I split your code to make it work. I put the C function exporting in an .h file, and the body itself in a .c file, and included only the h file in the go code.

dummy.h:

void testc();

dummy.c:

#include <sys/types.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>


void testc(){
    dummy();
}

main.go:

package main

// #cgo CFLAGS: -Wno-error=implicit-function-declaration
// #include <stdlib.h>
// #include "dummy.h"
import "C"

import "fmt"

//export dummy
func dummy() int {
    fmt.Println("hi you")
    return 0
}

func main() {
    C.testc()
}

answered Apr 13, 2015 at 13:25

Not_a_Golfer

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4 Comments

packetie Over a year ago

Thanks for the quick reply. When I ran it, got error ./main.go:33: undefined reference to `testc'

Not_a_Golfer Over a year ago

@codingFun how did you run it? I ran it with go build -o dummy && ./dummy

Not_a_Golfer Over a year ago

go build invokes cgo behind the scenes, generating wrapper files etc etc. you can run cgo directly on the code to see what it does.

packetie Over a year ago

Thanks @Not_a_Golfer, I ran it as "go run main.go" and got the error with loader/ld. Ran it your way (using go build..), it works great. Thanks again. I have accepted your answer and upvoted it!

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