Golang Cgo: panic: 运行时错误：cgo 参数具有指向 Go 指针的 Go 指针

huangapple
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英文:

Golang Cgo: panic: runtime error: cgo argument has Go pointer to Go pointer

问题

我正在使用一个C库，与下面的代码不同，我无法控制它。我需要向一个C函数传递一个包含指针的数组的指针。

  1. package main
  3. /*
  4. #include <stdio.h>
  6. typedef int* pInt;
  8. void foo(pInt p[]) {
  9.   printf("foo()\n");
  10. }
  11. */
  12. import "C"
  13. import "unsafe"
  15. func main() {
  16.     var i C.int
  17.     var p1 C.pInt = (*C.int)(unsafe.Pointer(&i))
  18.     var p2 C.pInt = (*C.int)(unsafe.Pointer(&i))
  19.     var ps []C.pInt = []C.pInt{p1, p2}
  20.     C.foo(unsafe.Pointer(&ps[0]))
  21. }

这段代码会导致错误panic: runtime error: cgo argument has Go pointer to Go pointer。我想知道如何重写这段代码的Go部分，以满足Cgo的指针规则。我希望能够在不编写C辅助代码的情况下完成这个任务。

英文:

I am working with a C library that, unlike below, I do not control. I need to pass to a C function a pointer to an array that also contains pointers.

  1. package main
  3. /*
  4. #include &lt;stdio.h&gt;
  6. typedef int* pInt;
  8. void foo(pInt p[]) {
  9.   printf(&quot;foo()\n&quot;);
  10. }
  11. */
  12. import &quot;C&quot;
  13. import &quot;unsafe&quot;
  15. func main() {
  16. 	var i C.int
  17. 	var p1 C.pInt = (*C.int)(unsafe.Pointer(&amp;i))
  18. 	var p2 C.pInt = (*C.int)(unsafe.Pointer(&amp;i))
  19. 	var ps []C.pInt = []C.pInt{p1, p2}
  20. 	C.foo(unsafe.Pointer(&amp;ps[0]))
  21. }

This code results in the error panic: runtime error: cgo argument has Go pointer to Go pointer. I am wondering how I can rewrite the Go portion of this code so that it satisfies Cgo's pointer rules. My hope is that I can do this without having to write C helper code.

答案1

得分: 6

坏消息是，你必须用C语言来定义你的辅助函数。
好消息是，只需要两行代码。

  1. package main
  3. /*
  4. #include <stdlib.h> // for malloc/free
  5. #include <stdio.h>
  7. typedef int* pInt;
  9. void foo(pInt p[]) { // you probably wanna pass a len to the function.
  10.     *p[0] = 100;
  11.     printf("foo()\n");
  12. }
  14. pInt * allocArray(size_t ln) { return (pInt*) malloc(ln * sizeof(pInt)); }
  15. void freeArr(pInt * p) { free(p); }
  17. */
  18. import "C"
  19. import "unsafe"
  21. func main() {
  22.     var (
  23.         i, sz  = 0, 2
  24.         arr    = C.allocArray(C.size_t(sz))
  25.         ps     = (*[100000]C.pInt)(unsafe.Pointer(arr))[:sz:sz]
  26.         p1, p2 = (C.pInt)(unsafe.Pointer(&i)), (C.pInt)(unsafe.Pointer(&i))
  27.     )
  28.     ps[0], ps[1] = p1, p2
  29.     C.foo(arr)
  30.     C.freeArr(arr)
  31.     println("i", i)
  32. }

希望对你有所帮助！

英文:

Bad news, you have to define your helpers in C.
Good news, well it's only 2 lines.

  1. package main
  3. /*
  4. #include &lt;stdlib.h&gt; // for malloc/free
  5. #include &lt;stdio.h&gt;
  7. typedef int* pInt;
  9. void foo(pInt p[]) { // you probably wanna pass a len to the function.
  10. 	*p[0] = 100;
  11. 	printf(&quot;foo()\n&quot;);
  12. }
  14. pInt * allocArray(size_t ln) { return (pInt*) malloc(ln * sizeof(pInt)); }
  15. void freeArr(pInt * p) { free(p); }
  17. */
  18. import &quot;C&quot;
  19. import &quot;unsafe&quot;
  21. func main() {
  22. 	var (
  23. 		i, sz  = 0, 2
  24. 		arr    = C.allocArray(C.size_t(sz))
  25. 		ps     = (*[100000]C.pInt)(unsafe.Pointer(arr))[:sz:sz]
  26. 		p1, p2 = (C.pInt)(unsafe.Pointer(&amp;i)), (C.pInt)(unsafe.Pointer(&amp;i))
  27. 	)
  28. 	ps[0], ps[1] = p1, p2
  29. 	C.foo(arr)
  30. 	C.freeArr(arr)
  31. 	println(&quot;i&quot;, i)
  32. }

答案2

得分: 5

修改OneOfOne的解决方案，不使用C辅助函数，尽管在go文件的注释中看到编写C辅助函数是多么容易。

  1. package main
  3. /*
  4. #include <stdio.h>
  6. typedef int* pInt;
  8. void foo(pInt p[]) { // you probably wanna pass a len to the function.
  9.     *p[0] = 100;
  10.     printf("foo()\n");
  11. }
  13. */
  14. import "C"
  15. import "unsafe"
  17. func main() {
  18.     var (
  19.         i, sz  = 0, 2
  20.         arr    = (*C.pInt)(C.malloc(C.size_t(sz)))
  21.         ps     = (*[100000]C.pInt)(unsafe.Pointer(arr))[:sz:sz]
  22.         p1, p2 = (C.pInt)(unsafe.Pointer(&i)), (C.pInt)(unsafe.Pointer(&i))
  23.     )
  24.     ps[0], ps[1] = p1, p2
  25.     C.foo(arr)
  26.     C.free(unsafe.Pointer(arr))
  27.     println("i", i)
  28. }
英文:

Modifying OneOfOne's solution without the C helper functions, although it is nice to see how easy C helper functions are to write in the comments of the go file.

  1. package main
  3. /*
  4. #include &lt;stdio.h&gt;
  6. typedef int* pInt;
  8. void foo(pInt p[]) { // you probably wanna pass a len to the function.
  9.     *p[0] = 100;
  10.     printf(&quot;foo()\n&quot;);
  11. }
  13. */
  14. import &quot;C&quot;
  15. import &quot;unsafe&quot;
  17. func main() {
  18. 	var (
  19. 		i, sz  = 0, 2
  20. 		arr    = (*C.pInt)(C.malloc(C.size_t(sz)))
  21. 		ps     = (*[100000]C.pInt)(unsafe.Pointer(arr))[:sz:sz]
  22. 		p1, p2 = (C.pInt)(unsafe.Pointer(&amp;i)), (C.pInt)(unsafe.Pointer(&amp;i))
  23. 	)
  24. 	ps[0], ps[1] = p1, p2
  25. 	C.foo(arr)
  26. 	C.free(unsafe.Pointer(arr))
  27. 	println(&quot;i&quot;, i)
  28. }

huangapple
  • 本文由 发表于 2016年3月11日 02:35:00
  • 转载请务必保留本文链接：https://go.coder-hub.com/35924545.html
  • cgo
  • go
  • pointers
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