cgo : 未定义的体系结构符号 x86_64

Question

我想从 C 函数中调用 go func space，但是程序抛出构建错误。

example.go

package main

/*
#include "test.c"
*/
import "C"
import "fmt"

func Example() {
    fmt.Println("this is go")
    fmt.Println(C.GoString(C.myprint(C.CString("go!!"))))
}

// export receiveC              (remove the extra space between // and export)
func receiveC(msg *C.char) {
    fmt.Println(C.GoString(msg))
}

func main() {
    Example()
}

test.c

#include <stdio.h>

extern void receiveC(char *msg);

char* myprint(char *msg) {
    receiveC(msg);  // calling the exported go function
    return msg;     
    }

当我对run/build（go build或go run example.go或go build example.go）程序执行命令时，它抛出错误：

# github.com/subh007/goodl/cgo
Undefined symbols for architecture x86_64:
  "_receiveC", referenced from:
      _myprint in example.cgo2.o
      __cgo_6037ec60b2ba_Cfunc_myprint in example.cgo2.o
      _myprint in test.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

我正在按照cgo slides写程序。如有任何错误，请告诉我。

Edit1：我正在使用 OS-X 10.9 OS。

编辑2：我在// export之间多了一个space，//和export之间应该没有space。但是现在我在构建时遇到以下错误：

# github.com/subh007/goodl/cgo
duplicate symbol _myprint in:
    $WORK/github.com/subh007/goodl/cgo/_obj/_cgo_export.o
    $WORK/github.com/subh007/goodl/cgo/_obj/example.cgo2.o
duplicate symbol _receiver_go in:
    $WORK/github.com/subh007/goodl/cgo/_obj/_cgo_export.o
    $WORK/github.com/subh007/goodl/cgo/_obj/example.cgo2.o
duplicate symbol _myprint in:
    $WORK/github.com/subh007/goodl/cgo/_obj/_cgo_export.o
    $WORK/github.com/subh007/goodl/cgo/_obj/test.o
duplicate symbol _receiver_go in:
    $WORK/github.com/subh007/goodl/cgo/_obj/_cgo_export.o
    $WORK/github.com/subh007/goodl/cgo/_obj/test.o
ld: 4 duplicate symbols for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

生成了重复的符号，因为我已经将 test.c 直接包含到 go 文件中。所以符号被包含了两次。

我认为，这段代码的正确写法是（如有错误请评论）：

定义头文件(test.h):

 #ifndef TEST_H_
 #define TEST_H_

 char* myprint(char *msg);

 #endif

定义实现文件(test.c):

  #include <stdio.h>
  #include "test.h"

  extern void receiveC(char *msg);

  char* myprint(char *msg) {
      receiveC(msg);
      return msg;
   }

将 .h 文件包含到 go 文件 (example.go) :

  package main
  /*
  #include "test.h"
  */
  import "C"
  import "fmt"

  func Example() {
       fmt.Println("this is go")
       fmt.Println(C.GoString(C.myprint(C.CString("go!!"))))
   }

   // make sure that there should be no space between the `//` and `export`
   //export receiveC
   func receiveC(msg *C.char) {
         fmt.Println(C.GoString(msg))
   }

   func main() {
        Example()
   }

构建程序：
```
  go build
```
运行生成的可执行文件（生成的可执行文件带有 cgo 名称，需要一些调查才能找到原因）。
```
  $./cgo
```

cgo : 未定义的体系结构符号 x86_64

cgo : Undefined symbols for architecture x86_64

linker

go

cgo