cgo：架构 x86_64 的未定义符号

Question

我想从 C 函数空间调用 go func，但程序抛出构建错误。

示例.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;     
    }

当我执行命令来运行/构建（go build或go run example.go或go build example.go）程序时，它会抛出错误：

# 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 幻灯片编写程序。如果这里有任何错误，请告诉我。

Edit1：我使用的是 OS-X 10.9 操作系统。

Edit2：我在 之间有一个额外的空格，和// export之间不应该有空格。但现在我在构建时遇到以下错误：//export

# 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

生成重复的符号是因为我已将其test.c直接包含到 go 文件中。因此这些符号被包含两次。

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. 将文件包含到文件 (example.go).h中：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()
      }
   

4. 构建程序：

     go build
   

5. 运行生成的可执行文件（生成的可执行文件具有该cgo名称，需要进行一些调查才能找到原因）。

     $./cgo