Go与C语言的互操作 cgo

http://tonybai.com/2012/09/26/interoperability-between-go-and-c/

// foo.h

int count;
void foo();

//foo.c
#include "foo.h"

int count = ;
void foo() {
    printf("I am foo!\n");
}
 

//foo.go

package main

// #cgo LDFLAGS: -L ./ -lfoo
// #include <stdio.h>
// #include <stdlib.h>
// #include "foo.h"
import "C"
import "fmt“

func main() {
    fmt.Println(C.count)
    C.foo()
}

使用静态库

$> gcc -c foo.c

$> ar rv libfoo.a foo.o

[diego@localhost ~/GoWork/src/applycation/testCgo]# go build foo.go
[diego@localhost ~/GoWork/src/applycation/testCgo]# ./foo 

I am foo!

[diego@localhost ~/GoWork/src/applycation/testCgo]# gcc -fPIC -shared -o libfoo.so foo.c
[diego@localhost ~/GoWork/src/applycation/testCgo]# rm li
libfoo.a   libfoo.so*
[diego@localhost ~/GoWork/src/applycation/testCgo]# rm libfoo.a
[diego@localhost ~/GoWork/src/applycation/testCgo]# go build fo
foo*    foo.c   foo.go  foo.h   foo.o
[diego@localhost ~/GoWork/src/applycation/testCgo]# go build foo.
foo.c   foo.go  foo.h   foo.o
[diego@localhost ~/GoWork/src/applycation/testCgo]# go build foo.go
[diego@localhost ~/GoWork/src/applycation/testCgo]# ./foo 

I am foo!
[diego@localhost ~/GoWork/src/applycation/testCgo]#

http://tonybai.com/2012/09/26/interoperability-between-go-and-c/

与在Go中使用C源码相比，在C中使用Go函数的场合较少。在Go中，可以使用"export + 函数名"来导出Go函数为C所使用，看一个简单例子：

 

package main

 

/*

#include <stdio.h>

 

extern void GoExportedFunc();

 

void bar() {

        printf("I am bar!\n");

        GoExportedFunc();

}

*/

import "C"

 

import "fmt"

 

//export GoExportedFunc

func GoExportedFunc() {

        fmt.Println("I am a GoExportedFunc!")

}

 

func main() {

        C.bar()

}

 

不过当我们编译该Go文件时，我们得到了如下错误信息：

 

# command-line-arguments

/tmp/go-build163255970/command-line-arguments/_obj/bar.cgo2.o: In function `bar':

./bar.go:7: multiple definition of `bar'

/tmp/go-build163255970/command-line-arguments/_obj/_cgo_export.o:/home/tonybai/test/go/bar.go:7: first defined here

collect2: ld returned 1 exit status

 

代码似乎没有任何问题，但就是无法通过编译，总是提示“多重定义”。翻看Cgo的文档，找到了些端倪。原来

 

There is a limitation: if your program uses any //export directives, then the C code in the comment may only include declarations (extern int f();), not definitions (int f() { return 1; }).

 

似乎是// extern int f()与//export f不能放在一个Go源文件中。我们把bar.go拆分成bar1.go和bar2.go两个文件：

 

// bar1.go

 

package main

 

/*

#include <stdio.h>

 

extern void GoExportedFunc();

 

void bar() {

        printf("I am bar!\n");

        GoExportedFunc();

}

*/

import "C"

 

func main() {

        C.bar()

}

 

// bar2.go

 

package main

 

import "C"

import "fmt"

 

//export GoExportedFunc

func GoExportedFunc() {

        fmt.Println("I am a GoExportedFunc!")

}

 

编译执行：

 

$> go build -o bar bar1.go bar2.go

$> bar

I am bar!

I am a GoExportedFunc!

 

Go代码：

func TestCallback() {
    f1 := syscall.NewCallback(PlusOne)
    f2 := syscall.NewCallbackCDecl(PlusTwo)
    var m uint32 = 20
    var n uint32 = 80

    // Func1 __stdcall
    fmt.Println(C.Func1(C.uint(m), (*[0]byte)(unsafe.Pointer(f1)))) // 21

    // Func2 __cdecl
    fmt.Println(C.Func2(C.uint(n), (*[0]byte)(unsafe.Pointer(f2)))) // 82
}

func PlusOne(n uint32) uintptr {
    return uintptr(n + 1)
}

func PlusTwo(n uint32) uintptr {
    return uintptr(n + 2)
}

C.Func1的第二个参数类型为函数，所以要传入一个*[0]byte。   http://studygolang.com/articles/2629

http://blog.giorgis.io/cgo-examples