CentOS C++数据库连接方法 - 问答

在CentOS系统上使用C++连接数据库，通常需要使用相应的数据库客户端库。以下是一些常见数据库的C++连接方法：

1. MySQL

安装MySQL客户端库

sudo yum install mysql-devel

示例代码

#include <mysql/mysql.h>
#include <iostream>

int main() {
    MYSQL *conn;
    MYSQL_RES *res;
    MYSQL_ROW row;

    conn = mysql_init(NULL);

    if (!mysql_real_connect(conn, "localhost", "user", "password", "database", 0, NULL, 0)) {
        fprintf(stderr, "%s\n", mysql_error(conn));
        exit(1);
    }

    if (mysql_query(conn, "show tables")) {
        fprintf(stderr, "%s\n", mysql_error(conn));
        exit(1);
    }

    res = mysql_use_result(conn);

    while ((row = mysql_fetch_row(res)) != NULL) {
        printf("%s \n", row[0]);
    }

    mysql_free_result(res);
    mysql_close(conn);

    return 0;
}

2. PostgreSQL

安装PostgreSQL客户端库

sudo yum install postgresql-devel

示例代码

#include <libpq-fe.h>
#include <iostream>

int main() {
    PGconn *conn = PQconnectdb("host=localhost dbname=database user=user password=password");

    if (PQstatus(conn) != CONNECTION_OK) {
        std::cerr << "Connection to database failed: " << PQerrorMessage(conn) << std::endl;
        PQfinish(conn);
        return 1;
    }

    PGresult *res = PQexec(conn, "SELECT * FROM table_name");

    if (PQresultStatus(res) != PGRES_TUPLES_OK) {
        std::cerr << "SELECT failed: " << PQerrorMessage(conn) << std::endl;
        PQclear(res);
        PQfinish(conn);
        return 1;
    }

    int rows = PQntuples(res);
    for (int i = 0; i < rows; i++) {
        std::cout << PQgetvalue(res, i, 0) << std::endl;
    }

    PQclear(res);
    PQfinish(conn);

    return 0;
}

3. SQLite

安装SQLite

sudo yum install sqlite-devel

示例代码

#include <sqlite3.h>
#include <iostream>

int main() {
    sqlite3 *db;
    char *err_msg = 0;
    int rc;

    rc = sqlite3_open("test.db", &db);

    if (rc != SQLITE_OK) {
        std::cerr << "Cannot open database: " << sqlite3_errmsg(db) << std::endl;
        sqlite3_close(db);
        return 1;
    }

    const char *sql = "CREATE TABLE IF NOT EXISTS COMPANY("
                      "ID INT PRIMARY KEY     NOT NULL,"
                      "NAME           TEXT    NOT NULL,"
                      "AGE            INT     NOT NULL,"
                      "ADDRESS        CHAR(50),"
                      "SALARY         REAL );";

    rc = sqlite3_exec(db, sql, 0, 0, &err_msg);

    if (rc != SQLITE_OK) {
        std::cerr << "SQL error: " << err_msg << std::endl;
        sqlite3_free(err_msg);
        sqlite3_close(db);
        return 1;
    }

    sqlite3_close(db);

    return 0;
}

编译和运行

对于上述示例代码，你可以使用以下命令进行编译：

g++ -o myapp myapp.cpp -lmysqlclient  # 对于MySQL
g++ -o myapp myapp.cpp -lpq         # 对于PostgreSQL
g++ -o myapp myapp.cpp -lsqlite3    # 对于SQLite

然后运行生成的可执行文件：

./myapp

请根据你的实际需求和数据库类型选择合适的库和示例代码。

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