将一个切片从C语言传递给Go语言时，是否会进行内存复制？

huangapple
go评论164阅读模式
英文:

Does passing a slice to golang from c do a memory copy?

问题

我需要将一个大块的float32（或byte）数据从C传递给一个Go库。

以下是代码：

  1. package main
  3. import (
  4.     "C"
  5.     "fmt"
  6. )
  8. //export PrintInt
  9. func PrintInt(x []float32) {
  10.     fmt.Println(x)
  11. }
  13. func main() {}

使用go build -buildmode=c-archive foo.go编译后，我得到了foo.h，以下是其中的一部分内容：

  1. typedef GoInt64 GoInt;
  2. typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;
  4. #endif
  6. /* End of boilerplate cgo prologue.  */
  8. #ifdef __cplusplus
  9. extern "C" {
  10. #endif
  13. extern void PrintInt(GoSlice p0);
  15. #ifdef __cplusplus
  16. }
  17. #endif

你可以看到，在foo.h中，类型GoSlice持有一个指向数据的指针（void *data）。那么，在foo.h中的PrintInt实现是否对该数据进行了隐式复制？

英文:

I need to pass a big chunk for float32 (or byte) from C to a go library.

Here is the code:

  1. package main
  3. import (
  4.         "C"
  5.         "fmt"
  6. )
  8. //export PrintInt                                                                                                     
  9. func PrintInt(x []float32) {
  10.         fmt.Println(x)
  11. }
  13. func main() {}

After compile it with go build -buildmode=c-archive foo.go

I got foo.h, here of a part of it:

  1. typedef GoInt64 GoInt;
  2. typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;
  4. #endif
  6. /* End of boilerplate cgo prologue.  */
  8. #ifdef __cplusplus
  9. extern "C" {
  10. #endif
  13. extern void PrintInt(GoSlice p0);
  15. #ifdef __cplusplus
  16. }
  17. #endif

You can see that type GoSlice in foo.h holds a pointer to the data (void *data). So does the implementation of PrintInt in foo.h do an implicit copy of that data?

答案1

得分: 3

我尝试在Go端修改数据，然后在C端进行反映。所以它们共享同一块内存。

foo.go:

  1. package main
  3. import (
  4. 	"C"
  5. 	"fmt"
  6. )
  8. //export PrintInt
  9. func PrintInt(x []float32) {
  10. 	fmt.Println(x)
  11. 	for i := range x {
  12. 		x[i] = -float32(i)
  13. 	}
  14. }
  16. func main() {}

foo.c:

  1. #include <stdio.h>
  3. #include "foo.h"
  5. int main() {
  6.   float bar[32];
  7.   for(int i = 0; i < 32; i++) {
  8.     bar[i] = i;
  9.   }
  11.   GoSlice s;
  12.   s.data = (void*)bar;
  13.   s.len = 32;
  14.   s.cap = 32;
  15.   PrintInt(s);
  17.   for(int i = 0; i < 32; i++) {
  18.     printf("%f ", bar[i]);
  19.   }
  21.   return 0;
  22. }

使用以下命令编译和运行：

  1. go build -buildmode=c-archive foo.go
  2. cc foo.c foo.a -o 123 && ./123

我得到的输出是：

[0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
26 27 28 29 30 31]
-0.000000 -1.000000 -2.000000 -3.000000 -4.000000 -5.000000 -6.000000 -7.000000 -8.000000 -9.000000 -10.000000 -11.000000 -12.000000 -13.000000 -14.000000 -15.000000 -16.000000 -17.000000 -18.000000 -19.000000 -20.000000 -21.000000 -22.000000 -23.000000 -24.000000 -25.000000 -26.000000 -27.000000 -28.000000 -29.000000 -30.000000 -31.000000

英文:

I tried to modify the data from go side, it is reflected in C. So they share same memory.

foo.go:

  1. package main
  3. import (
  4. 	&quot;C&quot;
  5. 	&quot;fmt&quot;
  6. )
  8. //export PrintInt
  9. func PrintInt(x []float32) {
  10. 	fmt.Println(x)
  11. 	for i := range x {
  12. 		x[i] = -float32(i)
  13. 	}
  14. }
  16. func main() {}

foo.c:

  1. #include &lt;stdio.h&gt;
  3. #include &quot;foo.h&quot;
  5. int main() {
  6.   float bar[32];
  7.   for(int i = 0; i &lt; 32; i++) {
  8.     bar[i] = i;
  9.   }
  11.   GoSlice s;
  12.   s.data = (void*)bar;
  13.   s.len = 32;
  14.   s.cap = 32;
  15.   PrintInt(s);
  17.   for(int i = 0; i &lt; 32; i++) {
  18.     printf(&quot;%f &quot;, bar[i]);
  19.   }
  21.   return 0;
  22. }

With command:

  1. go build -buildmode=c-archive foo.go
  2. cc foo.c foo.a -o 123 &amp;&amp; ./123

I got output:

> [0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
> 26 27 28 29 30 31]
> -0.000000 -1.000000 -2.000000 -3.000000 -4.000000 -5.000000 -6.000000 -7.000000 -8.000000 -9.000000 -10.000000 -11.000000 -12.000000 -13.000000 -14.000000 -15.000000 -16.000000 -17.000000 -18.000000 -19.000000 -20.000000 -21.000000 -22.000000 -23.000000 -24.000000 -25.000000 -26.000000 -27.000000 -28.000000 -29.000000 -30.000000 -31.000000

huangapple
  • 本文由 发表于 2017年4月27日 08:15:41
  • 转载请务必保留本文链接：https://go.coder-hub.com/43646589.html
  • cgo
  • go
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