MySQL - 如何在 C 使用

要先安裝好 MySQL ，取得 libmysqlclient.so 之後

用 dlopen 將會用到的 func 都找出來

之後就可以直接使用了~

或在編譯時加 -lmysqlclient 直接使用 func

放在 lib.so 裡

    #include<dlfcn.h>
    #define MYSQL_SHARE_LIB_PATH "/usr/lib/libmysqlclient.so"

    static int func_open_f = 0;

    static void *handle = NULL;
    static int( * _mysql_connect)(MYSQL * mysql,char *charset);
    static int( * _mysql_query)(MYSQL * mysql,char *format, ...);
    static void( * _mysql_close)(MYSQL * sock);
    static my_bool( * _mysql_reconnect)(MYSQL * mysql);

    MYSQL_RES * (STDCALL * my_mysql_store_result) (MYSQL * mysql);
    my_ulonglong(STDCALL * my_mysql_num_rows) (MYSQL_RES * res);
    my_ulonglong(STDCALL * my_mysql_affected_rows) (MYSQL * mysql);
    MYSQL_ROW(STDCALL * my_mysql_fetch_row) (MYSQL_RES * result);
    void(STDCALL * my_mysql_free_result) (MYSQL_RES * result);
    void(STDCALL * my_mysql_data_seek) (MYSQL_RES * result, my_ulonglong offset);
    unsigned int(STDCALL * my_mysql_errno) (MYSQL * mysql);
    const char *(STDCALL * my_mysql_error) (MYSQL * mysql);
    int(STDCALL * my_mysql_ping) (MYSQL * mysql);
    MYSQL_RES * (STDCALL * my_mysql_use_result) (MYSQL * mysql);
    unsigned int(STDCALL * my_mysql_num_fields) (MYSQL_RES * result);
    MYSQL_FIELD * (STDCALL * my_mysql_fetch_fields) (MYSQL_RES * result);

    static void function_close (void) {
        if (handle) {
            dlclose(handle);
            handle = NULL;
        }
        func_open_f = 0;
    }

    static void function_open (void) {
        if (handle != NULL)
            function_close();

        if ((handle = dlopen(MYSQL_SHARE_LIB_PATH, RTLD_LAZY))) {
            if (!(_mysql_connect = dlsym(handle, "MySQL_CONNECT")))
                goto err_close;

            if (!(_mysql_reconnect = dlsym(handle, "mysql_reconnect")))
                goto err_close;

            if (!(_mysql_query = dlsym(handle, "MySQL_QUERY")))
                goto err_close;

            if (!(my_mysql_store_result = dlsym(handle, "mysql_store_result")))
                goto err_close;

            if (!(my_mysql_num_rows = dlsym(handle, "mysql_num_rows")))
                goto err_close;

            if (!(my_mysql_fetch_row = dlsym(handle, "mysql_fetch_row")))
                goto err_close;

            if (!(my_mysql_affected_rows = dlsym(handle, "mysql_affected_rows")))
                goto err_close;

            if (!(my_mysql_free_result = dlsym(handle, "mysql_free_result")))
                goto err_close;

            if (!(_mysql_close = dlsym(handle, "mysql_close")))
                goto err_close;

            if (!(my_mysql_data_seek = dlsym(handle, "mysql_data_seek")))
                goto err_close;

            if (!(my_mysql_errno = dlsym(handle, "mysql_errno")))
                goto err_close;

            if (!(my_mysql_error = dlsym(handle, "mysql_error")))
                goto err_close;

            if (!(my_mysql_ping = dlsym(handle, "mysql_ping")))
                goto err_close;

            if (!(my_mysql_use_result = dlsym(handle, "mysql_use_result")))
                goto err_close;

            if (!(my_mysql_num_fields = dlsym(handle, "mysql_num_fields")))
                goto err_close;

            if (!(my_mysql_fetch_fields = dlsym(handle, "mysql_fetch_fields")))
                goto err_close;

            func_open_f = 1;
            return;
        }
    err_close:
        function_close();
    }

    int my_mysql_connect (MYSQL * mysql,char *charset) {
        #define RETRY_TIMES 10
        int times = RETRY_TIMES, result = -1;

        if (!func_open_f)
            function_open();

        if (!func_open_f)
            return result;

        /* connect mysql */
        while (times-- > 0) {
            if ((result = _mysql_connect(mysql, charset)) >= 0)
                break;

            sleep(1);
        }

        return result;
    }

    int my_mysql_query (MYSQL * mysql,char *format, ...) {
        va_list arg;
        int times = 5, result = -1;
        char *query = NULL;


        if (!func_open_f)
            function_open();

        if (!func_open_f)
            return result;

        va_start(arg, format);
        vasprintf( & query, format, arg);
        va_end(arg);

        if (query) {
            while (times-- > 0) {
                if ((result = _mysql_query(mysql, "%s", query)) >= 0)
                    break;

                /* Duplicate entry */
                if (my_mysql_errno(mysql) == 1062)
                    break;

                while (_mysql_reconnect(mysql)) sleep(1);

                sleep(2);
            }

            if (times <= 0)
                syslog(LOG_ERR, "Can't run this query: %s", query);

            free(query);
        }

        return result;
    }

    void my_mysql_close(MYSQL * mysql) {
        _mysql_close(mysql);
    }

使用方法

    MYSQL mysql;
    MYSQL_RES *res = NULL;
    MYSQL_ROW row;
    if (my_mysql_connect(&mysql, NULL) < 0)
        return;
    if(my_mysql_query(&mysql, "SELECT * FROM `%s`.`%s`", "db_name", "tb_name") != 0)
        return;
    if ((res = my_mysql_store_result(&mysql))) {
        while ((row = my_mysql_fetch_row(res))) {
            printf("%s, %s", row[0], row[1]);
        }
        my_mysql_free_result(res);
    }
    my_mysql_close(&mysql);