How to call c in golang

During the development process, we may need to use some libraries or plug-ins of C language, and Go language also provides some functions for using C language libraries so that we can call C language code in Go language. Let's learn together how to call C language code in Go language.

1. Using C language functions in Go language

In Go language, through the "C" package provided by the standard library, you can easily call C language functions and obtain their return values. When using the "C" package in the standard library, you need to add "C" after the import statement. The example is as follows:

package main

/*
#cgo CFLAGS: -I.
#cgo LDFLAGS: -L. -lxxx
#include "xxx.h"
*/
import "C"

func main() {
    // 调用C语言的函数
    result := C.xxx()
    // 处理返回值
    ...
}

Among them, CFLAGS and LDFLAGS are compilation and linking options, and -I is used to specify the header. File path, -L is used to specify the library file path, -l specifies the library name to be linked (there is no need to specify the lib prefix and .so/.a suffix).

Header files containing C language code also need to be included with the "#include" directive before the import statement in order to call functions in C language in Go language.

2. Calling C language functions

In Go language, we can use C language function signature to call C language functions. The following is a basic example that shows how to call a C function from Go code and have its return wrapped as a Go type:

package main

/*
#include <stdio.h>

void hello() {
    printf("Hello, C language!
");
}
*/
import "C"

func main() {
    C.hello()
}

In this code, we use the "C" package The C language function name "hello" imported in , this function is defined in our C language file. When we call "C.hello()", the hello() function in the C language code is called.

When the return value of this function is output, it will output "Hello, C language!".

3. Pointer to pointer

Pointer to pointer can also call C language functions in Go language. Here is an example of using a pointer to a pointer:

package main

import "fmt"

/*
#include <stdlib.h>

void sort(int **arr, int len) {
    qsort(*arr, len, sizeof(int), compare);
}

int compare(const void *a, const void *b) {
    return *(int *)a - *(int *)b;
}
*/
import "C"

func main() {
    // 定义指针数组
    var arr *[3]*C.int
    var a [3]C.int
    a[0], a[1], a[2] = 3, 2, 1
    arr = &a

    // 转换指针数组成二级指针
    var p **C.int = (**C.int)(unsafe.Pointer(&arr))

    // 调用C语言代码
    C.sort(p, 3)

    // 打印排序后的结果
    fmt.Println(a[0], a[1], a[2])
}

Here we are using a pointer to a pointer, in this way the contents of an array can be passed to a C language function.

4. Structure

The structure in C language can also be called in Go language. The following is an example of using a structure:

package main

import "fmt"

/*
#include <stdlib.h>

typedef struct field {
    int value;
} Field;

Field *newField(int value) {
    Field *field = (Field *)malloc(sizeof(Field));
    field->value = value;
    return field;
}
*/
import "C"

type Field struct {
    Value int
}

func main() {
    // 调用C语言代码
    f := C.newField(C.int(10))

    // 输出结构体中的值
    fmt.Println(Field{int(f.value)})
}

Here, we define a type "Field", which will be composed of a C language structure. We also define a function "newField" that will create the "Field" structure by calling the C code and set its value to 10 in the C code.

Then we define a "Field" type value that contains the value of the structure created from the C language code. Finally, we view the value in this structure by printing the value.

5. Summary

This article introduces how to use Go language to call C language libraries and functions. When calling a C language library or function, the functions and structures in the C language header file need to be included into the Go language code through the "#include" directive. In Go language code, we use import to import C language function signatures and use the "C" package to call these functions. We learned how to call C language functions using pointers to pointers and structures.

Although the C language and the Go language have many similarities, there are also some differences between them. When using Go language to call C language functions, you need to carefully handle type, pointer and memory allocation issues. Sometimes it is necessary to convert a structure, string or array to the corresponding type in C language in order to call C language functions correctly. Resources must be released after the call is completed to avoid memory leaks.

In general, C language function calls in Go language are very convenient and relatively safe. Issues such as type conversion, pointers, and memory allocation need to be carefully handled during use. If C language code can be used correctly, Go language developers can avoid reinventing the wheel and use existing C language libraries and codes to improve code reusability and efficiency.

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