golang：我可以在包之间共享C.int吗？

huangapple
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英文:

golang: can i share C.int between packages

问题

在主包中，我有：

  1. var foo C.int
  2. foo = 3
  3. t := fastergo.Ctuner_new()
  4. fastergo.Ctuner_register_parameter(t, &foo, 0, 100, 1)

在fastergo包中，我有：

  1. func Ctuner_register_parameter(tuner unsafe.Pointer, parameter *C.int, from C.int, to C.int, step C.int) C.int {
  2. 	...
  3. }

如果我尝试运行它，我会得到以下错误：

  1. demo.go:14[/tmp/go-build742221968/command-line-arguments/_obj/demo.cgo1.go:21]: cannot use &foo (type *_Ctype_int) as type *fastergo._Ctype_int in function argument

我不太确定Go在这里试图告诉我什么，但我有种感觉它想告诉我，所有的C.int并不相等？为什么会这样？我该如何解决这个问题或绕过它？

英文:

in the main package i have:

  1. var foo C.int
  2. foo = 3
  3. t := fastergo.Ctuner_new()
  4. fastergo.Ctuner_register_parameter(t, &foo, 0, 100, 1)

in the fastergo package i have:

  1. func Ctuner_register_parameter(tuner unsafe.Pointer, parameter *C.int, from C.int, to C.int, step C.int) C.int {
  2. 	...
  3. }

if i try to run it, i get:

  1. demo.go:14[/tmp/go-build742221968/command-line-arguments/_obj/demo.cgo1.go:21]: cannot use &foo (type *_Ctype_int) as type *fastergo._Ctype_int in function argument

i am not really sure what go is trying to tell me here, but somehow i think it wants to tell me, that all C.int are not equal? why is this the case? how can i solve this / work around?

答案1

得分: 5

由于_Ctype_int不以Unicode大写字母开头，该类型是包内部的。在C包装器包中使用Go类型，将它们转换为C类型。包装器包应该隐藏所有实现细节。

您没有提供足够的信息，以便我们创建可以编译和运行的示例代码。以下是我期望看到的大致概述：

  1. package main
  3. import "tuner"
  5. func main() {
  6.     var foo int
  7.     foo = 3
  8.     t := tuner.New()
  9.     t.RegisterParameter(&foo, 0, 100, 1)
  10. }

.

  1. package tuner
  3. import (
  4.     "unsafe"
  5. )
  7. /*
  8. #include "ctuner.h"
  9. */
  10. import "C"
  12. type Tuner struct {
  13.     ctuner uintptr
  14. }
  16. func New() *Tuner {
  17.     var t Tuner
  18.     t.ctuner = uintptr(unsafe.Pointer(C.ctuner_new()))
  19.     return &t
  20. }
  22. func (t *Tuner) RegisterParameter(parameter *int, from, to, step int) error {
  23.     var rv C.int
  24.     rv = C.ctuner_register_parameter(
  25.         (*C.ctuner)(unsafe.Pointer(t.ctuner)),
  26.         (*C.int)(unsafe.Pointer(parameter)),
  27.         C.int(from),
  28.         C.int(to),
  29.         C.int(step),
  30.     )
  31.     if rv != 0 {
  32.         // 处理错误
  33.     }
  34.     return nil
  35. }
英文:

Since _Ctype_int doesn't begin with a Unicode upper case letter, the type is local to the package. Use Go types, except in the C wrapper package where you convert them to C types. The wrapper package should hide all the implementation details.

You don't provide sufficient information for us to create sample code which compiles and runs. Here's a rough outline of what I expected to see:

  1. package main
  3. import "tuner"
  5. func main() {
  6. 	var foo int
  7. 	foo = 3
  8. 	t := tuner.New()
  9. 	t.RegisterParameter(&foo, 0, 100, 1)
  10. }

.

  1. package tuner
  3. import (
  4. 	"unsafe"
  5. )
  7. /*
  8. #include "ctuner.h"
  9. */
  10. import "C"
  12. type Tuner struct {
  13. 	ctuner uintptr
  14. }
  16. func New() *Tuner {
  17. 	var t Tuner
  18. 	t.ctuner = uintptr(unsafe.Pointer(C.ctuner_new()))
  19. 	return &t
  20. }
  22. func (t *Tuner) RegisterParameter(parameter *int, from, to, step int) error {
  23. 	var rv C.int
  24. 	rv = C.ctuner_register_parameter(
  25. 		(*C.ctuner)(unsafe.Pointer(t.ctuner)),
  26. 		(*C.int)(unsafe.Pointer(parameter)),
  27. 		C.int(from),
  28. 		C.int(to),
  29. 		C.int(step),
  30. 	)
  31. 	if rv != 0 {
  32. 		// handle error
  33. 	}
  34. 	return nil
  35. }

答案2

得分: 0

根据peterSO的解释，你不能在包之间传递C.int。但是，你可以通过转换指针类型在包之间传递指针。为此，你需要在目标包中定义一个命名类型，将该类型导入到调用包中，并通过unsafe.Pointer进行转换。对于单个int来说，这样做没有任何意义。

但是，如果你将转换复杂类型的代码保留在一个包中，这将非常有帮助；例如，一个字符串数组（或任何类型的嵌套数组）。

下面的示例是将Go函数导出为在C中调用，但是这也可以反过来使用，即如果你想调用返回嵌套数组的C函数。

  1. package convert
  3. import "C"
  5. type PP_char **C.char
  6. func From_c_to_go(arr_str PP_char, length int) []string {
  7.     // 对C类型进行一些操作
  8.     var slice []string
  9.     for _, s := range unsafe.Slice(arr_str, length) {
  10.         if s == nil {
  11.             break
  12.         }
  13.         x := C.GoString(s)
  14.         slice = append(slice, x)
  15.     }
  16.     return slice
  17. }
  1. package main
  3. import "C"
  4. import "convert"
  6. //export myFunc
  7. func myFunc(arr_str **C.char, length int){
  8.     retyped_arr_str := convert.PP_char(unsafe.Pointer(arr_str))
  9.     slice := convert.From_c_to_go(retyped_arr_str, length)
  10.     // 对slice进行一些操作
  11. }

你也可以决定将unsafe.Pointer的实例作为参数传递给目标包中的go函数，并在该函数中执行类型转换。

英文:

As explained by peterSO, you can't pass C.int between packages. However, you can pass pointers between packages by converting the pointer type. To do this, you would define a named type in the target package, import that type into the calling package and covert via unsafe.Pointer. There isn't any point in doing this with a single int.

However, it is helpful if you keep code to convert complex types in a package; for example an array of strings (or any sort of nested array).

The example below is for exporting a go function to be called in C, but this works in reverse, ie. if you want to call a C functions which a returns nested array.

  1. package convert
  3. import "C"
  5. type PP_char **C.char
  6. func From_c_to_go(arr_str PP_char, length int) []string {
  7.     // Some operation on the Ctype
  8. 	var slice []string
  9. 	for _, s := range unsafe.Slice(arr_str, length) {
  10. 		if s == nil {
  11. 			break
  12. 		}
  13. 		x := C.GoString(s)
  14. 		slice = append(slice, x)
  15. 	}
  16. 	return slice
  17. }
  1. package main
  3. import "C"
  4. import "convert"
  6. //export myFunc
  7. func myFunc(arr_str **C.char, length int){
  8.     retyped_arr_str := convert.PP_char(unsafe.Pointer(arr_str))
  9.     slice := convert.From_c_to_go(retyped_arr_str, length)
  10.     // Do something with slice
  11. }

You could instead decide to pass instance of unsafe.Pointer as an argument to the go function in the target package and perform the type conversion in that function.

huangapple
  • 本文由 发表于 2013年7月26日 19:17:56
  • 转载请务必保留本文链接：https://go.coder-hub.com/17879961.html
  • cgo
  • go
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