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CGO passing a function pointer to C

·1 min
Golang Code-Snippet

By default when passing a function as an argument, Cgo uses unsafe.Pointer. This will result in an IncompatibleAssign error.

In order to pass a function pointer as an argument to a C function, type conversion must be used. In the example below (*[0]byte) is used to convert C.print_hello to what C.invoke expects. (*[0]byte) is special, it means the same as void * in C.

package main

/*
#include <stdio.h>

static void invoke(void (*f)()) {
	f();
}

void print_hello() {
	printf("Hello, World!\n");
}
*/
import "C"

func main() {
	C.invoke((*[0]byte)(C.print_hello))
}

Other workarounds #

Use typedef and explicitly convert to the type:

package main

/*
#include <stdio.h>

typedef void (*PrintHelloFn)();

static void invoke(void (*f)()) {
	f();
}

void printHello() {
	printf("Hello, World from C!\n");
}
*/
import "C"

func main() {
	C.invoke(C.PrintHelloFn(C.printHello))
}

IBM - CGO callbacks Passing callbacks and pointers to CGO Passing pointers CGO wiki