golang uses so method

Golang (also known as Go) is a programming language developed by Google, mainly for network applications and distributed systems. It has the advantages of efficient memory management and excellent concurrency performance, so it is favored by more and more developers. In Golang, we can use so files to implement library functions in languages ​​such as C, thereby improving our Golang programming and improving code reusability and flexibility. This article will discuss how to use the so method in Golang based on actual cases.

1. What is an so file?

so file, the full name is Shared Object File (Shared Object File), also known as Dynamic Linking Library (Dynamic Linking Library), is a reusable Locate the target file, which can be shared and called by different programs. In the Linux system, the dynamic link library is an important component. Various system libraries and applications can be provided in the form of so files, thereby facilitating the development and maintenance of applications. In C language, we can use the gcc command to compile the .c file into a .so file, and then link it to our application for use. In Golang, we can also use the cgo method to link the .so file to our program for calling.

2. Examples of using so files in Golang

Below we take the md5 calculation of Golang through so files as an example. The specific steps are as follows:

1. Write C Language code, generate .so file

We first write an md5.c file to calculate the md5 value:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/md5.h>

char* md5(char* str){
    MD5_CTX md5;
    MD5_Init(&md5);
    MD5_Update(&md5, str, strlen(str));
    unsigned char md[16];
    MD5_Final(md, &md5);

    char* result = (char*)malloc(sizeof(char) * 33);
    memset(result, '', sizeof(result));
    int i = 0;
    for(i = 0; i < 16; i++){
        sprintf(result + i * 2, "%02x", md[i]);
    }

    return result;
}

In this C language code, we use OpenSSL MD5 algorithm in the library to calculate md5 value. It should be noted that since Golang needs to use the cgo method to call C language, we need to add "// #include ", where "C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\include" is the header of the OpenSSL library in our MinGW compiler file path.

Next, we use the gcc command to compile md5.c into a .so file:

gcc -shared -o libmd5.so md5.c -fPIC -I /usr/local/opt/openssl/include -L /usr/local/opt/openssl/lib -lcrypto

In the above command,

• -shared specifies to generate a shared object file;
• -o specifies the output dynamic link library file name;
• md5.c is our source code file;
• -fPIC specifies that the generated code snippet position is irrelevant, and Can be shared among multiple applications;
• -I /usr/local/opt/openssl/include and -L /usr/local/opt/openssl/lib specify the path to the OpenSSL library file;
• -lcrypto specifies the link encryption library file.

2. Write Golang code

Next, we write a main.go file to call the md5 function in the .so file. The specific code is as follows:

package main

/*
#cgo LDFLAGS: -L./ -lmd5
#include <stdlib.h>

//引入C语言中的md5函数
char* md5(char* str);

//封装C语言函数，以便在Go中使用
char* c_md5(char* str){
    return md5(str);
}
*/
import "C"
import (
    "fmt"
    "unsafe"
)

func main() {
    str := "hello world"
    cstr := C.CString(str)
    defer C.free(unsafe.Pointer(cstr))

    md5 := C.GoString(C.c_md5(cstr))
    fmt.Println(md5)
}

In this Golang code, we use the cgo method to link the md5 function in C language with the Golang code, and call the md5 function of C language through Go language to calculate the md5 value of the string. It should be noted that first we used the comment "// #cgo LDFLAGS: -L./ -lmd5" to specify the path and name of the .so file, so that the Go language can correctly link the .so file during compilation;

Secondly, we declare the C language in the Go language through the two comments "//Introducing the md5 function in the C language" and "//Encapsulating the C language function for use in Go" md5 function, and encapsulates the C language function c_md5, so that we can easily call C language functions in Go language;

Finally, we convert the characters into C strings through the C.CString() function , and use C.GoString() at the end to convert the C string back to the string type in the Go language. It should also be noted that we need to manually call the C.free() function to release memory after using the C.CString() function to convert the string into C language characters to avoid memory leaks.

3. Summary

Through this simple case, we learned how to use the so method in Golang to improve our programming efficiency by linking C language library files. It should be noted that when using so files, we must pay attention to the paths of each file and the compiler and library versions. Especially on Mac OS systems, we may encounter version and support problems, so that in actual applications, Encountered some difficulties and problems. However, we believe that with the joint efforts of all developers, these problems will be solved step by step, and Golang's development efficiency will become higher and higher.

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