How to develop a simple file compression function using MySQL and C++

How to use MySQL and C to develop a simple file compression function

Introduction:
In the context of the development of modern science and technology, file compression and decompression technology has becomes a very important feature. By compressing files, you can reduce the file size and save storage space and transmission bandwidth. This article will introduce how to use MySQL and C to develop a simple file compression function, help readers understand the basic principles of compression algorithms, and give specific code examples.

1. Basic Principles of Compression Algorithms
The basic idea of ​​most file compression algorithms is to reduce the file size by using recurring patterns or using fewer bits to represent data. Common compression algorithms include Huffman coding, LZW coding, etc. In this article, we will use the Huffman coding algorithm to compress files.

Huffman coding is a variable-length coding that assigns shorter codewords to characters with higher frequency and longer codewords to characters with lower frequency, thereby making the entire encoding The average code length is minimized. The algorithm is divided into two main steps: building a Huffman tree and generating Huffman codes.

2. Method of storing compressed data in MySQL
In order to facilitate the storage and retrieval of compressed data, we can use MySQL's BLOB (Binary Large Object) data type to store compressed files. The BLOB type allows the storage of binary data, and the maximum length can be specified. The following is an example of creating a data table that saves compressed data:

CREATE TABLE compressed_files (

id INT AUTO_INCREMENT PRIMARY KEY,
filename VARCHAR(255),
compressed_data BLOB,
original_size INT,
compressed_size INT

);

3. C implements file compression function
Because of Ha Huffman coding is a relatively complex algorithm. Here we will use the open source Huffman coding library to implement file compression.

First, we need to install a C library, such as zlib (https://www.zlib.net/). After the installation is complete, we can use the functions provided by the zlib library to compress and decompress files.

The following is a simple example code for compressing a file and storing the compressed data into a MySQL database:

include

include

include

include

void compressFile(const char filename, const char compressedFilename) {

std::ifstream inputFile(filename, std::ios::binary);
std::ofstream compressedFile(compressedFilename, std::ios::binary);

if (!inputFile || !compressedFile) {
    std::cerr << "Failed to open file." << std::endl;
    return;
}

z_stream stream;
stream.zalloc = Z_NULL;
stream.zfree = Z_NULL;
stream.opaque = Z_NULL;
stream.avail_in = 0;
stream.next_in = Z_NULL;

if (deflateInit(&stream, Z_DEFAULT_COMPRESSION) != Z_OK) {
    std::cerr << "Failed to initialize deflate." << std::endl;
    return;
}

const int bufferSize = 1024 * 1024;
unsigned char inBuffer[bufferSize];
unsigned char outBuffer[bufferSize];

while (!inputFile.eof()) {
    inputFile.read(reinterpret_cast<char*>(inBuffer), bufferSize);
    stream.avail_in = inputFile.gcount();
    stream.next_in = inBuffer;

    do {
        stream.avail_out = bufferSize;
        stream.next_out = outBuffer;

        if (deflate(&stream, Z_FINISH) == Z_STREAM_ERROR) {
            std::cerr << "Failed to deflate." << std::endl;
            return;
        }

        compressedFile.write(reinterpret_cast<const char*>(outBuffer),
                             bufferSize - stream.avail_out);
    } while (stream.avail_out == 0);
}

deflateEnd(&stream);
inputFile.close();
compressedFile.close();

}

void saveCompressedDataToMySQL(const char* compressedFilename,

                           const char* mysqlHost,
                           const char* mysqlUser,
                           const char* mysqlPassword,
                           const char* mysqlDatabase) {
MYSQL* mysql = mysql_init(NULL);

if (!mysql_real_connect(mysql, mysqlHost, mysqlUser, mysqlPassword, mysqlDatabase, 0, NULL, 0)) {
    std::cerr << "Failed to connect to MySQL database." << std::endl;
    return;
}

std::ifstream compressedFile(compressedFilename, std::ios::binary);

if (!compressedFile) {
    std::cerr << "Failed to open file." << std::endl;
    return;
}

compressedFile.seekg(0, std::ifstream::end);
int compressedSize = compressedFile.tellg();
compressedFile.seekg(0, std::ifstream::beg);

char* compressedData = new char[compressedSize];
compressedFile.read(compressedData, compressedSize);

std::string insertQuery = "INSERT INTO compressed_files (filename, compressed_data, original_size, compressed_size) VALUES (?, ?, ?, ?)";
MYSQL_STMT* stmt = mysql_stmt_init(mysql);

if (mysql_stmt_prepare(stmt, insertQuery.c_str(), insertQuery.size()) != 0) {
    std::cerr << "Failed to prepare insert statement." << std::endl;
    delete[] compressedData;
    return;
}

MYSQL_BIND params[4];
memset(params, 0, sizeof(params));

// filename
std::string filename = "example.txt";
params[0].buffer_type = MYSQL_TYPE_VAR_STRING;
params[0].buffer = (char*)filename.c_str();
params[0].length = filename.size();

// compressed_data
params[1].buffer_type = MYSQL_TYPE_BLOB;
params[1].buffer = compressedData;
params[1].buffer_length = compressedSize;

// original_size
params[2].buffer_type = MYSQL_TYPE_LONG;
params[2].buffer = &originalSize;
params[2].is_unsigned = true;

// compressed_size
params[3].buffer_type = MYSQL_TYPE_LONG;
params[3].buffer = &compressedSize;
params[3].is_unsigned = true;

if (mysql_stmt_bind_param(stmt, params) != 0) {
    std::cerr << "Failed to bind parameters." << std::endl;
    delete[] compressedData;
    return;
}

if (mysql_stmt_execute(stmt) != 0) {
    std::cerr << "Failed to execute insert statement." << std::endl;
    delete[] compressedData;
    return;
}

mysql_stmt_close(stmt);
mysql_close(mysql);
compressedFile.close();
delete[] compressedData;

}

int main() {

const char* filename = "example.txt";
const char* compressedFilename = "example_compressed.bin";
const char* mysqlHost = "localhost";
const char* mysqlUser = "root";
const char* mysqlPassword = "password";
const char* mysqlDatabase = "test";

compressFile(filename, compressedFilename);
saveCompressedDataToMySQL(compressedFilename, mysqlHost, mysqlUser, mysqlPassword, mysqlDatabase);

return 0;

}

4. Summary
This article introduces how to use MySQL and C to develop a simple file compression function. By using the Huffman coding algorithm and the zlib library, we can quickly achieve file compression Decompress and decompress the data, and store the compressed data in the MySQL database. I hope this article can help readers understand the basic principles and implementation methods of file compression.

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