使用 Go 語言構建 C 庫

阿新 • • 發佈：2021-01-07

使用 Go 語言構建 C 庫

1.How to
- 1.1.Build Go package as C shared library (or shared object)
- 1.2.Generate C header and export Go functions as C functions
2.Example

CGO is an official builtin feature of Go, it enables the creation of Go packages that reference to C libraries. But it isn’t just that, it is achievable in the opposite direction, too. It enables creation of C libraries from Go packages so that C code can reference to Go, which is mind-blowing.

CGO 不但可以使 Go 包訪問 C 庫，還可以通過 Go 包建立 C 庫，進而使 C/C++ 程式可呼叫 Go 語言程式。

1.How to

1.1.Build Go package as C shared library (or shared object)

Every Go main package can be built as a C shared library.

任何 Go main 包都可以建立 C 庫。

go build -buildmode=c-shared -o <c-lib>.so

Executing above command builds target Go main

package and all of its dependencies as a single C shared library, which can be distributed, installed and linked to every C application and applications in other programming languages that can reference C shared libraries (C++, Python, Javascript, etc).

以上命令可以建立共享庫，該共享庫可以被 C、C++、Python、Javascript 等語言訪問。

Note: Output C shared libraries should be named in standard form lib*.so.

1.2.Generate C header and export Go functions as C functions

Building a Go main package as C shared library doesn’t automatically neither generate C header nor expose any Go function as C symbol. Developers have to explicitly indicate which Go functions to be exposed.

To export a Go function as a C symbol:

The function must belong to main package.
The Go code file containing the function has to import “C”.
Add comment //export FuncName on top of the Go function.
The function signature must not include neither Go struct nor* Go interface nor Go array nor variadic argument.

上述命令不會生成 C 標頭檔案並匯出符號。若想匯出符號並自動生成標頭檔案需要滿足以下條件：

要匯出的函式必須屬於 main 包；
Go 原始碼檔案包含 import “C”；
在要匯出的函式使用 //export FuncName 註釋；
不能使用 Go struct、Go interface、Go arra、以及可變引數。

2.Example

package main

import "C"

import (
    "math/rand"
    "time"
)

//export cgoCurrentMillis
func cgoCurrentMillis() C.long {
    return C.long(time.Now().Unix())
}

//export cgoSeed
func cgoSeed(m C.long) {
    rand.Seed(int64(m))
}

//export cgoRandom
func cgoRandom(m C.int) C.int {
    return C.int(rand.Intn(int(m)))
}

func main() {}

Building above Go main package generates a C header file <output>.h along with a C shared object <output>.so.

構建以上示例將自動產生標頭檔案和共享庫。

// Other stuff.

extern long int cgoCurrentMillis();
extern void cgoSeed(long int p0);
extern int cgoRandom(int p0);

cgoCurrentMilli, cgoSeed and cgoRandom are exposed as C symbols in <output>.so, too.

Now, every C application can include the generated C header, link to the output C shared library and use exposed C symbols.

#include <stdio.h>

int main() {
    cgoSeed(cgoCurrentMillis());

    printf("Hello World from C!\n");
    printf("cgoRandom() -> %d\n", cgoRandom(256));
    return 0;
}

編譯方法如下：

gcc main.c -l<c-lib> -o <exe-file>

使用 Go 語言構建 C 庫