golang与C交互:cgo

1. 在Go中引用C代码很简单, 在 import "C"前用注释引入标准的C代码, 然后使用C.xxx的伪包引用C代码空间的标识符即可. 需要注意, import"C"是伪package,不能与其他package一块定义为import (..."C"...)

2. 在Go中引用C代码必须手工释放C代码对象. 释放方法为C.free(unsafe.Pointer(xxx)), 这也要求C代码包含#include <stdlib.h>

3. 必须深入理解下述:

(1) Cgo recognizes this comment above import "C" statement. 

(2) Any lines starting with #cgo followed by a space character are removed; these become directives for cgo. 

(3) The remaining lines are used as a header when compiling the C parts of the package. 

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通俗记忆:

(1)cgo能够识别import "C" 语句的注释.

(2)#cgo行用作cgo指令

(3)其他行用作C头文件

第(2)点很关键! 容易导致重复定义.

实践问题:

代码段1:

-------------------------------

package main

/*

#include <stdlib.h>

#include "prints.h"

*/

import "C"

import (

"fmt"

"unsafe"

)

func main() {

msg := "this is a test for"

cmsg := C.CString(msg)

defer C.free(unsafe.Pointer(cmsg))

C.prints(cmsg)

fmt.Println("done...")

}

//在main包中引入C代码, 使用go run xxx.go会报错. 先go build-->再执行, 无错误. 

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上面解决办法,是定义wrapper把C代码封装起来. 例如:

package myc

/*

#include <stdlib.h>

#include "prints.h"

*/

import "C"

import "unsafe"

func Cprints(msg string) {

cmsg := C.CString(msg)

defer C.free(unsafe.Pointer(cmsg))

C.prints(cmsg)

}

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