英文:
How do I pass a **void pointer to C function? I am getting a cgo argument has Go pointer to Go pointer
问题
package main
//
// void test(void** data) {
// // 在这里执行一些操作...
// }
import "C"
import "unsafe"
func main() {
var data *C.void
cData := unsafe.Pointer(&data)
C.test(cData)
}
上面是我尝试做的一个示例，但是我收到一个运行时错误，错误信息是"cgo argument has Go pointer to Go pointer"。我该如何解决这个问题？有什么想法吗？
英文:
package main
//
// void test(data **void) {
// Do something here...
// }
import "C"
import "unsafe"
func main() {
var data *C.void
cData := unsafe.Pointer(&data)
C.test(cData)
}
Above is an example of what I am trying to do but I am receiving a run time error stating cgo argument has Go pointer to Go pointer. How do I resolve this issue? any ideas?
答案1
得分: 0
void* 在 Go 中的等价类型是 unsafe.Pointer，没有必要声明一个 *C.void 类型的值。你的示例中的错误不是关于一个指向 Go 指针的 Go 指针（这是一个运行时错误），你会得到一个 (variable of type unsafe.Pointer) as *unsafe.Pointer 的错误，这是无法编译的。使用错误中显示的类型：
func main() {
var data unsafe.Pointer
C.test(&data)
}
英文:
The Go equivalent of void* is an unsafe.Pointer, there's no reason to declare a value of *C.void. The error from your example is not about a Go pointer to a Go pointer (which is a runtime error), you will get an error of (variable of type unsafe.Pointer) as *unsafe.Pointer, which cannot compile. Use the type shown in the error:
func main() {
var data unsafe.Pointer
C.test(&data)
}
答案2
得分: -1
当你声明var data *C.void时，你是在说data是Go指针类型。Go中的所有指针都受垃圾回收的管理。
当将&data传递给unsafe.Pointer时，会创建另一个Go指针。这就是所谓的“Go指针到Go指针”。它的过程是&data -> data -> (void)。
在这种情况下，垃圾回收器无法确定何时释放data是合适的，因为&data指针被传递给了C，C仍然可以通过它访问data。
请参阅这篇文章了解有关将指针传递给C的更多信息。
除非关闭一些cgo检查（我不建议这样做），否则不可能实现这一点。
英文:
When you declare var data *C.void, you are saying that data are Go pointer type. All pointers in Go are subject of garbage collection.
When passing &data to unsafe.Pointer another Go pointer is created. Thats what the "Go pointer to Go pointer" means. It goes &data -> data -> (void).
In this case, garbage collector cannot decide when would be the right time to deallocate data, because &data pointer was passed to C, which can still reach data through it.
See this article about passing pointers to C.
It's not possible, unless you turn-off some of the cgo checks, which I would not recommend.
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