Comprehensive summary: Golang calls C/C++, example tutorial

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Foreword:

There are many tutorials on Golang calling C/C++ on the Internet. As far as I have seen so far, my personal opinion is rather messy and there are many pitfalls. I hope that this article can be made clearer to a certain extent.

Golang is abbreviated as go below, as always, no nonsense, we will start now.

The implementation methods of calling c/c++ functions in go are:

Use directly 嵌套in the go file, the most simple and intuitive
The import 动态库 .so 或 dllform is the safest but very uncomfortable and slower
Directly quote the form of c/c++ files, with clear levels, easy to modify at any time to see the results

The third 直接引用 c/c++ 文件的形式is the main point I want to introduce.

Environmental support required

Linux has gcc and g++
Windows needs to install mingw , otherwise there will be such errors when compiling:cannot find -lmingwex
Mac reference Linux

1, directly nested in the go file

package main
/*
// C 标志io头文件，你也可以使用里面提供的函数
#include <stdio.h> 

void pri(){
	printf("hey");
}

int add(int a,int b){
	return a+b;
}
*/
import "C"  // 切勿换行再写这个

import "fmt"

func main() {
	fmt.Println(C.add(2, 1))
}
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The above code, directly copy and run it will output the result: 3

in conclusion:

Whenever you want to reference related to the c / c ++ content, the file is written to the head go 注释inside
Nested c/c++ code must conform to its syntax, not the same as go
import "C" This sentence should be followed immediately, after the comment, do not wrap, otherwise an error will be reported
The format of calling c/c++ in go code is:, C.xxx()for example C.add(2, 1)

2. Import the dynamic library .so or .dll

Suppose the project directory is as follows

|-project
|  |-lib
|  |  |-libvideo.dll
|  |  |-libvideo.so
|  |-include
|  |  |-video.h
|  |-src
|  |  |-main.go
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The header file.h is as follows

//video.h
#ifndef VIDEO_H
#define VIDEO_H
void exeFFmpegCmd(char* cmd); // 声明
#endif
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The source file.c is as follows

#include <stdio.h>
#include "video.h"

void exeFFmpegCmd(char* cmd){ // 实现
    // ....
    printf("finish");
}
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Use gcc or g++ to generate .so library, or generate dll under win

E.g: gcc video.c -fPIC -shared -o libvideo.so

Finally main.go

Put the dynamic library in a directory you like, or in the current project, just like the examples listed above. Requote

package main

/*
#cgo CFLAGS: -Iinclude
#cgo LDFLAGS: -Llib -llibvideo
#include "video.h"
*/
import "C"

import "fmt"

func main() {
   cmd := C.CString("ffmpeg -i ./xxx/*.png ./xxx/yyy.mp4")
   C.exeFFmpegCmd(&cmd)
}
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First answer why this is the safest and most uncomfortable? The reasons are as follows:

The dynamic library is very difficult to crack. If your go code is leaked, the core dynamic library will not be easily compromised.
The dynamic library will be loaded when it is used, affecting the speed
Operation difficulty is much more troublesome than method one

in conclusion

CFLAGS: -I路径 This sentence indicates the path of the header file, -Iinclude indicates the include folder of the current project root directory
LDFLAGS: -L路径 -l名字 Specify the path of the dynamic library, -Llib -llibvideo, specify under the lib and its name video
If the dynamic library does not exist, 找不到定义之类an error message will be exploded

3. The form of directly referencing c/c++ files `（重点）`

Suppose the project directory is as follows

|-util
|  |-util.h
|  |-util.c
|  |-util.go
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util.h

int sum(int a,int b);
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util.c

#include "util.h"
int sum(int a,int b){
    return (a+b);
}
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util.go

package util

/*
#include "util.c"
*/
import "C"

import "fmt"

func GoSum(a,b int) {
    s := C.sum(C.int(a),C.int(b))
    fmt.Println(s)
}
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Call main.go like this

package main

func main(){
    util.GoSum(4,5)
}
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This is the third way 简洁明了.

Finally, add, need to go to call general c / c ++, mainly using some well-known open source libraries, such as ffmpeg, , opencvand other such source code is based on c / c ++ language, in addition to a very important point, they Is the running speed!

Author: Lin Guanhong _ fingertips under the specter
link: https: //juejin.im/post/6844903553132134414