此文章主要向大家讲述的是MySQL数据库中的MySQL_real_connect 连接参数的基本设置，我们在前一篇文章讲述关于进行MySQL(和PHP搭配之最佳组合)源程序代码的编译链接，但是没有讲述运行情况，在按照上一篇文章代码下进行编译运行后。
发现无法链接数据库文件，显然是在MySQL(和PHP搭配之最佳组合)_real_connect（）函数中出现了问题。在MySQL(和PHP搭配之最佳组合)的英文手册中找到关于MySQL(和PHP搭配之最佳组合)_real_connect()的如下描述：
函数原型描述 MySQL数据库*MySQL(和PHP搭配之最佳组合)_real_connect(MySQL(和PHP搭配之最佳组合) *MySQL(和PHP搭配之最佳组合), const char *host, const char
*user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag) Description MySQL(和PHP搭配之最佳组合)_real_connect() attempts to establish a connection to a MySQL(和PHP搭配之最佳组合) database engine running on host. MySQL(和PHP搭配之最佳组合)_real_connect() must complete successfully before you can execute any other API functions that require a valid MySQL(和PHP搭配之最佳组合) connection handle structure. The parameters are specified as follows: * The first parameter should be the address of an existing MySQL(和PHP搭配之最佳组合) structure. Before calling MySQL(和PHP搭配之最佳组合)_real_connect() you must call MySQL(和PHP搭配之最佳组合)_init() to initialize the MySQL(和PHP搭配之最佳组合) structure. You can change a lot of connect options with the MySQL(和PHP搭配之最佳组合)_options() call. See Section 17.2.3.47, “MySQL(和PHP搭配之最佳组合)_options()”. * The value of host may be either a hostname or an IP address. If host is NULL or the string "localhost", a connection to the local host is assumed. If the OS supports sockets (Unix) or named pipes (Windows), they are used instead of TCP/IP to connect to the server. * The user parameter contains the user's MySQL(和PHP搭配之最佳组合) login ID. If user is NULL or the empty string "", the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current username must be specified explicitly. See Section 18.1.9.2, “Configuring a MyODBC DSN on Windows”. * The passwd parameter contains the password for user. If passwd is NULL, only entries in the user table for the user that have a blank (empty) password field are checked for a match. This allows the database administrator to set up the MySQL(和PHP搭配之最佳组合) privilege system in such a way that users get different privileges depending on whether they have specified a password. Note: Do not attempt to encrypt the password before calling MySQL(和PHP搭配之最佳组合)_real_connect(); password encryption is handled automatically by the client API. * db is the database name. If db is not NULL, the connection sets the default database to this value. * If port is not 0, the value is used as the port number for the TCP/IP connection. Note that the host parameter determines the type of the connection. * If unix_socket is not NULL, the string specifies the socket or named pipe that should be used. Note that the host parameter determines the type of the connection. * The value of client_flag is usually 0, but can be set to a combination of the following flags to enable certain features:
上面描述了五个参数的主要取值，MySQL数据库 *为MySQL(和PHP搭配之最佳组合)_init函数返回的指针，host为null或 // localhost时链接的是本地的计算机，当MySQL(和PHP搭配之最佳组合)默认安装在unix（或类unix）系统中，root账户是没// 有密码的，因此用户名使用root，密码为null，当db为空的时候，函数链接到默认数据库，在进行 // MySQL(和PHP搭配之最佳组合)安装时会存在默认的test数据库，因此此处可以使用test数据库名称，port端口为0，使用 // unix连接方式，unix_socket为null时，表明不使用socket或管道机制，最后一个参数经常设置为0
Flag Name Flag Description CLIENT_COMPRESS Use compression protocol. CLIENT_FOUND_ROWS Return the number of found (matched) rows, not the number of changed rows. CLIENT_IGNORE_SPACE Allow spaces after function names. Makes all functions names reserved words. CLIENT_INTERACTIVE Allow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. The client's session wait_timeout variable is set to the value of the session interactive_timeout variable. CLIENT_LOCAL_FILES Enable LOAD DATA LOCAL handling. CLIENT_MULTI_STATEMENTS Tell the server that the client may send multiple statements in a single string (separated by ‘;Â’). If this flag is not set, multiple-statement execution is disabled. Added in MySQL(和PHP搭配之最佳组合) 4.1. CLIENT_MULTI_RESULTS Tell the server that the client can handle multiple result sets from multiple-statement executions or stored procedures. This is automatically set if CLIENT_MULTI_STATEMENTS is set. Added in MySQL(和PHP搭配之最佳组合) 4.1. CLIENT_NO_SCHEMA Don't allow the db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs. CLIENT_ODBC The client is an ODBC client. This changes MySQL(和PHP搭配之最佳组合)d to be more ODBC-friendly. CLIENT_SSL Use SSL (encrypted protocol). This option should not be set by application programs; it is set internally in the client library. Instead, use MySQL(和PHP搭配之最佳组合)_ssl_set() before calling MySQL(和PHP搭配之最佳组合)_real_connect(). For some parameters, it is possible to have the value taken from an option file rather than from an explicit value in the MySQL(和PHP搭配之最佳组合)_real_connect() call. To do this, call MySQL(和PHP搭配之最佳组合)_options() with the MySQL(和PHP搭配之最佳组合)_READ_DEFAULT_FILE or MySQL(和PHP搭配之最佳组合)_READ_DEFAULT_GROUP option before calling MySQL(和PHP搭配之最佳组合)_real_connect(). Then, in the MySQL(和PHP搭配之最佳组合)_real_connect() call, specify the “no-value” value for each parameter to be read from an option file: * For host, specify a value of NULL or the empty string (""). * For user, specify a value of NULL or the empty string. * For passwd, specify a value of NULL. (For the password, a value of the empty string in the MySQL(和PHP搭配之最佳组合)_real_connect() call cannot be overridden in an option file, because the empty string indicates explicitly that the MySQL(和PHP搭配之最佳组合) account must have an empty password.) * For db, specify a value of NULL or the empty string. * For port, specify a value of 0. * For unix_socket, specify a value of NULL. If no value is found in an option file for a parameter, its default value is used as indicated in the descriptions given earlier in this section. Return Values A MySQL(和PHP搭配之最佳组合)* connection handle if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first parameter.
返回值：当连接成功时，返回MySQL数据库连接句柄，失败，返回NULL。当成功时，返回值与第一个参数值是// 相同的。
Errors * CR_CONN_HOST_ERROR Failed to connect to the MySQL(和PHP搭配之最佳组合) server. * CR_CONNECTION_ERROR Failed to connect to the local MySQL(和PHP搭配之最佳组合) server. * CR_IPSOCK_ERROR Failed to create an IP socket. * CR_OUT_OF_MEMORY Out of memory. * CR_SOCKET_CREATE_ERROR Failed to create a Unix socket. * CR_UNKNOWN_HOST Failed to find the IP address for the hostname. * CR_VERSION_ERROR A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the --old-protocol option. * CR_NAMEDPIPEOPEN_ERROR Failed to create a named pipe on Windows. * CR_NAMEDPIPEWAIT_ERROR Failed to wait for a named pipe on Windows. * CR_NAMEDPIPESETSTATE_ERROR Failed to get a pipe handler on Windows. * CR_SERVER_LOST If connect_timeout > 0 and it took longer than connect_timeout seconds to connect to the server or if the server died while executing the init-command.
因此MySQL(和PHP搭配之最佳组合)_real_connect()函数调用为：
MySQL(和PHP搭配之最佳组合)_real_connect(MySQL数据库,"localhost","root",NULL,"test",0,NULL,0);
判断是否出错，出错调用MySQL(和PHP搭配之最佳组合)_error()函数显示出错信息，或使用MySQL(和PHP搭配之最佳组合)_errno()函数获取出错代号。