// Simple C function call.

C.f0()

// Call with constant.

C.f1(5)

// Call with Go int - cast to C int.

var i int = 8

C.f1(C.int(i))

// Convert Go string to C string (char*) and back.

cs := C.CString("Go string")

csRet := C.f2(cs)

fmt.Printf("fmt: %s\n", C.GoString(csRet))

C.free(unsafe.Pointer(cs)) // free memory right now ...

defer C.free(unsafe.Pointer(csRet)) // ... or later

// Pass C struct to C function by value.

s1 := C.struct_s1{a: 5} // or cast with C.int: s1 := C.struct_s1{C.int(i)}

s1Ret := C.f31(s1)

fmt.Printf("f31: s1=%v, s1Ret=%v\n", s1, s1Ret)

// Pass C struct to C function by pointer.

s1 = C.struct_s1{a: 5}

s1Ret = *C.f32(&s1)

fmt.Printf("f32: s1=%v, s1Ret=%v\n", s1, s1Ret)

// Pass C struct with int pointer to C function.

// s2 := C.struct_s2{&C.int(i)} - compile error "cannot take the address of _Ctype_int(i)", create variable as below

ci := C.int(i)

s2 := C.struct_s2{p: &ci}

fmt.Printf("s2=%v, *s2.p=%d, i=%d\n", s2, *s2.p, i)

C.f4(s2)

fmt.Printf("f4: s2=%v, *s2.p=%d, i=%d\n", s2, *s2.p, i)

// Pass C function pointer to C function.

// C.f5(C.f1) - compile error "must call C.f1"

// fp := unsafe.Pointer(C.f1) - compile error "must call C.f1"

// It is not possible to pass C function pointer via Go.

// Pass C function pointer to C function with simple C wrapper (see top of this file).

C.call_f5_with_f1()

// Pass Go function pointer to C function.

f := func(i C.int) {

fmt.Println("Go f()")

}

fp := unsafe.Pointer(&f)

// C.f5((*[0]byte)(fp)) - Compiles but explodes. Do not do this!

// Pass global Go function pointer to C function.

f = F

fp = unsafe.Pointer(&f)

// C.f5((*[0]byte)(fp)) - Compiles but explodes. Do not do this!

// It is possible to call Go function from C. See main2.go for solution.

_ = fp