MySQL 嵌入式伺服器 開發入門：從編譯到執行完整範例

MySQL Embedded Server (libmysqld) 允許將 MySQL 伺服器庫直接鏈結進應用程式，無需獨立 mysqld 進程，適合桌面應用、測試工具、邊緣裝置等場景。官方文檔年久失修，本文提供基於 MySQL 5.5/5.6 可直接編譯執行的最小化 C++ 範例。

一、編譯安裝 Embedded Library

# 來源碼目錄下
cmake . -DCMAKE_INSTALL_PREFIX=/home/mysql -DWITH_EMBEDDED_SERVER=1
make clean && make -j8
make install

安裝後 /home/mysql/lib/libmysqld.a 即為靜態庫，動態庫為 libmysqld.so。

二、專案結構

$ ls
GNUmakefile  main.cc  my.cnf

GNUmakefile

# 假設 MySQL 安裝在 /home/mysql
topdir := /home/mysql/mysql-5.5.35
inc    := $(topdir)/include
lib    := $(topdir)/libmysqld

CXX      := g++
CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT
CXXFLAGS := -g -Wall
LDFLAGS  :=
LDLIBS   := -L$(lib) -lmysqld -lm -lcrypt -ldl -lz -lrt -pthread

sources := $(wildcard *.cc)
objects := $(patsubst %.cc,%.o,$(sources))
targets := $(basename $(sources))

all: $(targets)

clean:
    rm -f $(targets) $(objects) *.core

my.cnf（嵌入式專用配置）

[libmysqld_client]
[libmysqld_server]
basedir=/home/mysql/
datadir=/home/mysql/data
tmpdir=/home/mysql/tmp
log-error=/home/mysql/alert.log
lc_messages_dir=/home/mysql/share

innodb_data_home_dir=/home/mysql/data
innodb_log_group_home_dir=/home/mysql/data

main.cc 核心程式碼

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

using namespace std;

const char *server_options[] = {
    "mysql_test", "--defaults-file=my.cnf", NULL
};
int num_elements = (sizeof(server_options) / sizeof(char *)) - 1;

const char *server_groups[] = {
    "libmysqld_server", "libmysqld_client", NULL
};

bool is_server_started = false;
MYSQL *MySQL = NULL;
const char *db = NULL;

void start_server() {
    cout << "enter start_server()" << endl;
    if (mysql_library_init(num_elements, (char**)server_options, (char**)server_groups)) {
        is_server_started = false;
        cout << "ERROR: start server failed." << endl;
    } else {
        is_server_started = true;
        cout << "INFO: start server OK." << endl;
    }
}

void stop_server() {
    cout << "enter stop_server()" << endl;
    mysql_server_end();
}

bool connect_server() {
    cout << "enter connect_server()" << endl;
    bool rc = true;
    MySQL = mysql_init(NULL);
    if (!MySQL) return rc;
    if (mysql_real_connect(MySQL, NULL, NULL, NULL, db, 0, NULL, 0))
        rc = false;
    MySQL->reconnect = 1;
    return rc;
}

void output_rows(MYSQL_RES *res) {
    MYSQL_ROW row;
    unsigned long n = 0;
    while ((row = mysql_fetch_row(res)) != 0) {
        mysql_field_seek(res, 0);
        for (unsigned int i = 0; i < mysql_num_fields(res); i++)
            cout << "row[" << n++ << "]: " << row[i] << endl;
    }
}

bool get_dbs() {
    MYSQL_RES *res;
    if (!is_server_started) return true;
    if (!(res = mysql_list_dbs(MySQL, "%"))) return true;
    output_rows(res);
    mysql_free_result(res);
    return false;
}

int main(int argc, char *argv[]) {
    start_server();
    if (is_server_started) {
        cout << "server started." << endl;
        if (!connect_server()) {
            get_dbs();
        }
        stop_server();
    }
    return 0;
}

三、初始化資料目錄並執行

cd /home/mysql
scripts/mysql_install_db --defaults-file=/home/mysql/my.cnf

# 編譯並執行
make
./main

四、關鍵點總結

• mysql_library_init() 傳入 server_options 與 server_groups，對應 my.cnf 區段名
• 連線時 host=NULL, user=NULL, passwd=NULL 表示使用本地嵌入式協議
• mysql_server_end() 必須配對呼叫，否則資料檔可能損壞
• 執行緒安全：連結 -pthread，定義 _THREAD_SAFE、_REENTRANT
• 若需切換為 Client/Server 模式，將 -lmysqld 改為 -lmysqlclient，程式碼無需修改

五、現狀提醒

MySQL 8.0 起官方不再維護 Embedded Server，MariaDB 同樣已棄用。新專案建議考慮：