CGO error : cannot use f ( type func(_Ctype_int, **_Ctype_char) _Ctype_int) as *[0]byte value in argument

[ulis lee]

Hi, all

It's been a month since I started Golang.
But I was in a difficult situation. I need your help.

C code

int reopen (const char *fn, time_t check_interval_sec, int (*callback_func) (int num_entry, char **entry), int retry);

Go code

func _Open(fileName string, intervalSec int, f func(C.int, **C.char) C.int) int {

   cFileName := C.CString(fileName)

   defer C.free(unsafe.Pointer(cFileName))

    ret := C.reopen(cFileName, C.long(intervalSec), f, 1)

    return int(ret)

}

error message 
cannot use f (variable of type func(_Ctype_int, **_Ctype_char) _Ctype_int) as *[0]byte value in argument to (_Cfunc_reopen)

[Tzu-Yu Lee]

Hi,

You cannot pass f, which is a Go function, in a CGo call directly because of the pointer passing rules. You need to create some wrappers, and I have found this article (https://eli.thegreenplace.net/2019/passing-callbacks-and-pointers-to-cgo) very helpful.

That being said, I have a feeling that if you provide some more details about what you are trying to achieve, people here might be able to help you get a simpler solution in Go.

Tzu-Yu

ulis lee 在 2023年11月22日 星期三上午11:28:20 [UTC+8] 的信中寫道：

[Kurtis Rader]

I think the error is trying to tell you the C reopen function takes a pointer to a function and you are passing it a Go func. Try googling "cgo pass function pointer". That should yield documents like https://eli.thegreenplace.net/2019/passing-callbacks-and-pointers-to-cgo/ which should point you in the right direction. I have to say, trying to do something like this after using Go for just one month is very ambitious. I think you are going to run into lots of problems due to your lack of experience with Go (not Golang).

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Kurtis Rader

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