golang與C互動:cgo

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

1. 在Go中引用C代碼很簡單, 在 import "C"前用注釋引入標準的C代碼, 然後使用C.xxx的偽包引用C代碼空間的標識符即可. 需要注意, import"C"是偽package,不能與其他package一塊定義為import (..."C"...)

2. 在Go中引用C代碼必須手工釋放C代碼對象. 釋放方法為C.free(unsafe.Pointer(xxx)), 這也要求C程式碼封裝含#include <stdlib.h>

3. 必須深入理解下述:

(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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通俗記憶:

(1)cgo能夠識別import "C" 語句的注釋.

(2)#cgo行用作cgo指令

(3)其他行用作C標頭檔

第(2)點很關鍵! 容易導致重複定義.

實踐問題:

程式碼片段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代碼, 使用go run xxx.go會報錯. 先go build-->再執行, 無錯誤. 

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上面解決辦法,是定義wrapper把C代碼封裝起來. 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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