How to call c language method in uniapp

With the continuous development of mobile Internet applications, the development needs of application programs are becoming more and more diverse. Writing programs in C language can often achieve higher performance, so combining C language with mobile application platforms has become a trend. How to call C language methods in the process of developing mobile applications using the uniapp framework is a topic that developers often face. This article will introduce how to implement methods and techniques for calling C language methods under the uniapp framework.

1. The principle of calling C language methods by uniapp

The basic principle of calling C language methods under the uniapp framework is to compile the C language program into a library file, and then import the library file into In the uniapp project. In the uniapp project, the C language program is called through js code to implement the function. Currently, in the field of mobile applications, the more common C language libraries include libjpeg, libpng, libsqlite, etc. The following takes the libjpeg library as an example to introduce the compilation and import of C language library files.

2. Compilation of C language library files

1. Download the source code file to the local

Download the corresponding C language library source code file online and extract it to in a local folder.

2. Use CMake to generate Makefile files

CMake is a cross-platform build tool that can be used to generate Makefile files. On Mac and Linux platforms, you can directly enter the following command on the console to generate a Makefile:

$ cmake .

Note that there is a dot here, which means that the Makefile is generated in the current directory.

3. Use make to generate the library file

Enter the following command in the console to generate the libjpeg library file:

$ make

4. Import the file into the uniapp project

Copy the generated library file to the platforms/xx/lib/ directory under the root directory of the uniapp project. Among them, xx represents the development platform chosen by the developer (such as android, ios, etc.).

3. Using C language library files in uniapp

In the uniapp project, it is relatively simple to use js code to call C language library files. First, import the C language library that needs to be called in the .js file, and then call the corresponding function through the method name.

1. Use the ffi-napi library to import C language library files

In the uniapp project, we can use the ffi-napi library to import C language library files. ffi-napi is a Node.js library for calling native C code.

You can install ffi-napi in the project through the following instructions:

$ npm install ffi-napi

Then import the ffi-napi library in the .js file:

const ffi = require('ffi-napi')

After importing the library file, we need to create an object pointing to the library file in order to call the function in js. We need to use the ffi.Library() command to create an object to connect to the library file and encapsulate the methods contained in the library. The following is a simple example of using the ffi-napi library to call a C language library file:

const libjpeg = new ffi.Library('libjpeg', {
'jpeg_read_header': [ 'int', [ ' pointer', 'int' ] ]
})

In the above code, we instantiate an object pointing to the libjpeg library file and encapsulate the jpeg_read_header() method contained in it. This method accepts Takes a pointer and an integer as arguments and returns an integer.

2. Call the function in the C language library file

When calling the method in the C language library file, we need to pass the correct parameters and receive the return value according to the return type of the method. The following is an example of calling the jpeg_read_header() method in the above C language library file:

const jpeg_filename = '/path/to/jpegfile.jpg'
const cfilenameptr = Buffer.from(jpeg_filename '\0 ') // Construct pointer data
const header = Buffer.alloc(512) // Create an empty buffer area to receive the return value

const ret = libjpeg.jpeg_read_header(cfilenameptr, header.length)
if (ret === 0) {
console.log('Error: Unable to read file header information!')
} else {
console.log('Read successfully!')
}

In the above code, we use Buffer.from() to create a pointer data pointing to the jpeg file name. Then read the file header information by calling the jpeg_read_header() method, and store the return value in the cache header. Based on the return value, we can determine whether the program is executed successfully. If 0 is returned, the program execution failed.

Summary

Through the above content, we can know that under the uniapp framework, the process of calling C language library files is relatively simple. First, you need to compile the C language program into a library file, and then import the library file into the uniapp project. Finally, we can use the ffi-napi library to import the C language library file and call the functions in the library file in the .js file to implement the function of using the C language program in the uniapp project.

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