How to use golang cgo

Golang is a relatively young programming language, but due to its efficient and minimalist design philosophy, it has become the first choice for many developers. In addition, Golang also has a feature that supports function and library calls written in C language. This feature is implemented through the cgo package. This article will introduce the usage and precautions of Golang cgo.

Overview:

Cgo is a standard package of Golang that can connect Golang programs and C language libraries.
Cgo is actually the abbreviation of CGO, and its full name is "C language calling GO language". Using the cgo package makes it easy to develop using C language libraries.
Using Cgo can also increase the performance of the program, because programs written in C language are often faster than Golang.

Using Cgo in Golang can directly call C language functions in Golang code without first declaring the function as a function pointer and then converting it into a pointer of size uintptr through the unsafe package. At the same time, you can also directly let C language functions operate Golang's memory. At the same time, you can pass the structure in Golang to the C language library and use it in C language.

Usage:

1. The CGO_ENABLED environment variable must be set to 1:

   $ export CGO_ENABLED=1

2. Define Cgo code, define it in the code C language functions:

   package main
   import "C"
   //export MyFunction
   func MyFunction(name *C.char){
    // your code here
   }

3. Write C language library:

   #include <stdio.h>
   void myFunction(char* name){
    printf("Hello,%s", name);
   }

4. Export C language functions to Golang:

   package main
   /*
   #include <stdlib.h>
   void myFunction(char*name);
   #cgo LDFLAGS: -L. -lmylibrary
   */
   import "C"
   
   func main() {
    name:= C.CString("world")
    defer C.free(unsafe.pointer(name))
    C.myFunction(name)
   }

5. Compile the C language library and link:

   $ gcc -c -o mylibrary.o mylibrary.c
   $ gcc -shared -o libmylibrary.so mylibrary.o

6. Compile and execute the Golang program:

   $ go build -o main main.go
   $ ./main

Notes:

1. When using Cgo to call a C language function, you need to declare the function as an exported function starting with the "C" keyword.
2. All types used in exported functions, such as pointers, structures, etc., must be defined by the C language header file.
3. When passing a Golang structure to a C language function, type conversion is required.
4. In Cgo programs, direct operations on Golang data structures, such as the use of slices, should be minimized. Because Golang's memory management mechanism is different from that of C language, direct operation will cause problems.

Summary:

Cgo is a necessary means to use the C language library in Golang language. Mastering the usage and precautions of Cgo can help us develop using Golang more efficiently, conveniently and safely, and improve the performance and stability of the program.

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