go - CGO : Undefined symbols for architecture x86_64

Question

我想从 C 函数空间调用 go func，但程序抛出构建错误。

例子.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()
}

测试.c

#include <stdio.h>

extern void receiveC(char *msg);

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

当我执行运行/构建命令(go build 或 go run example.go 或 go build example.go)时程序，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)

我正在关注 cgo slides编写程序。如有任何错误，请告诉我。

Edit1:我使用的是 OS-X 10.9 操作系统。

编辑2: 我在//export之间多了一个空格，//和export之间应该没有空格。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

生成重复符号是因为我将 test.c 直接包含到 go 文件中。所以这些符号被包含了两次。

我认为，编写这段代码的正确方法是(如果我错了请评论):

1. 定义头文件(test.h):

    #ifndef TEST_H_
    #define TEST_H_
   
    char* myprint(char *msg);
   
    #endif
   

2. 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;
      }
   

3. 将 .h 文件包含到 go 文件 (example.go) 中:

     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()
      }
   

4. 构建程序:

     go build
   

5. 运行生成的可执行文件(以cgo 名称生成的可执行文件，需要一些调查才能找到原因)。

     $./cgo