How to perform file and database operations in C++?

How to perform file and database operations in C?

In C programming, file and database operations are very common tasks. File operations are used to read and write data to disk files, while database operations are used to store and retrieve data with a database. This article describes how to perform file and database operations in C and provides corresponding code examples.

1. File operations

In C, file operations are implemented by using the fstream library. The library provides functions and data types for opening, reading, writing, and closing files.

1. Open a file

To open a file, you first need to include the header file and create a file stream object. The file can then be opened using the open() function.

#include <fstream>
using namespace std;

int main() {
    ofstream file("example.txt"); // 创建一个输出文件流对象
    
    if (file.is_open()) {
        // 文件成功打开，可以进行读写操作
        // ...
        
        file.close(); // 关闭文件
    }
    else {
        // 文件打开失败
        cout << "无法打开文件" << endl;
    }
    
    return 0;
}

2. Write to file

After opening the file, you can use the write operator (<<) to write data to the file.

#include <fstream>
using namespace std;

int main() {
    ofstream file("example.txt"); // 创建一个输出文件流对象
    
    if (file.is_open()) {
        file << "Hello, World!" << endl; // 写入数据到文件
        file.close(); // 关闭文件
    }
    else {
        cout << "无法打开文件" << endl;
    }
    
    return 0;
}

3. Reading files

To read data from a file, use the input file stream object and read the data using the input operator (>>) Get it into a variable.

#include <fstream>
using namespace std;

int main() {
    ifstream file("example.txt"); // 创建一个输入文件流对象
    string line;
    
    if (file.is_open()) {
        while (getline(file, line)) {
            cout << line << endl; // 输出文件的每一行数据
        }
        
        file.close(); // 关闭文件
    }
    else {
        cout << "无法打开文件" << endl;
    }
    
    return 0;
}

2. Database operation

Database operations require the use of database drivers and related API libraries. In C, you can use libraries such as ODBC and MySQL Connector/C to interact with the database. The following uses the MySQL Connector/C library as an example to introduce the basic steps of database operations.

1. Connecting to the database

To connect to the database, you need to include the corresponding header file and create a connection object. Then, use the connect() function of this connection object to connect to the database.

#include <mysql_driver.h>
#include <mysql_connection.h>
using namespace std;

int main() {
    sql::mysql::MySQL_Driver *driver; // 创建MySQL驱动程序对象
    sql::Connection *conn; // 创建连接对象
    
    driver = sql::mysql::get_mysql_driver_instance(); // 获取MySQL驱动程序实例
    conn = driver->connect("tcp://127.0.0.1:3306", "root", "password"); // 连接数据库
    
    if (conn) {
        // 数据库连接成功
        // ...
        
        conn->close(); // 关闭数据库连接
        delete conn; // 释放连接对象
    }
    else {
        cout << "数据库连接失败" << endl;
    }
    
    return 0;
}

2. Execute SQL query

After connecting to the database, you can use the createStatement() function of the connection object to create a statement object. Then, use the executeQuery() function of this statement object to execute the SQL query.

#include <mysql_driver.h>
#include <mysql_connection.h>
using namespace std;

int main() {
    // 连接数据库代码省略...
    
    if (conn) {
        sql::Statement *stmt; // 创建语句对象
        sql::ResultSet *res; // 创建结果集对象
        
        stmt = conn->createStatement(); // 创建语句对象
        res = stmt->executeQuery("SELECT * FROM students"); // 执行SQL查询
        
        while (res->next()) {
            cout << "ID: " << res->getInt("id") << ", Name: " << res->getString("name") << endl; // 输出查询结果
        }
        
        delete res; // 释放结果集对象
        delete stmt; // 释放语句对象
        
        conn->close(); // 关闭数据库连接
        delete conn; // 释放连接对象
    }
    else {
        cout << "数据库连接失败" << endl;
    }
    
    return 0;
}

The above are the basic steps and sample codes for file and database operations in C. Through these code examples, you can implement file and database-related functions in C programs. Hope this article is helpful to you!

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