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21.9.3.52. mysql_real_connect()

MYSQL *mysql_real_connect(MYSQL *mysql, 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_real_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_real_connect() must complete successfully before you can execute any other API functions that require a valid MYSQL connection handle structure.

The parameters are specified as follows:

  • The first parameter should be the address of an existing MYSQL structure. Before calling mysql_real_connect() you must call mysql_init() to initialize the MYSQL structure. You can change a lot of connect options with the mysql_options() call. See Section 21.9.3.49, “mysql_options()”.

  • The value of host may be either a host name or an IP address. If host is NULL or the string "localhost", a connection to the local host is assumed: For Windows, the client connects using a shared-memory connection, if the server has shared-memory connections enabled. Otherwise, TCP/IP is used. For Unix, the client connects using a Unix socket file. For local connections, you can also influence the type of connection to use with the MYSQL_OPT_PROTOCOL or MYSQL_OPT_NAMED_PIPE options to mysql_options(). The type of connection must be supported by the server. For a host value of "." on Windows, the client connects using a named pipe, if the server has named-pipe connections enabled. If named-pipe connections are not enabled, an error occurs.

  • The user parameter contains the user's MySQL 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 user name must be specified explicitly. See the MyODBC section of Chapter 21, Connectors and APIs.

  • 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 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_real_connect(); password encryption is handled automatically by the client API.

  • The user and passwd parameters use whatever character set has been configured for the MYSQL object. By default, this is latin1, but can be changed by calling mysql_options(mysql, MYSQL_SET_CHARSET_NAME, "charset_name") prior to connecting.

  • 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.

    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_SIGPIPE Prevents the client library from installing a SIGPIPE signal handler. This can be used to avoid conflicts with a handler that the application has already installed.
    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_RESULTS Tell the server that the client can handle multiple result sets from multiple-statement executions or stored procedures. This flag is automatically enabled if CLIENT_MULTI_STATEMENTS is enabled. See the note following this table for more information about this flag.
    CLIENT_MULTI_STATEMENTS Tell the server that the client may send multiple statements in a single string (separated by “;”). If this flag is not set, multiple-statement execution is disabled. See the note following this table for more information about this flag.
    CLIENT_NO_SCHEMA Do not 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 Unused.
    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_ssl_set() before calling mysql_real_connect().
    CLIENT_REMEMBER_OPTIONS Remember options specified by calls to mysql_options(). Without this option, if mysql_real_connect() fails, you must repeat the mysql_options() calls before trying to connect again. With this option, the mysql_options() calls need not be repeated.

If your program uses CALL statements to execute stored procedures, the CLIENT_MULTI_RESULTS flag must be enabled. This is because each CALL returns a result to indicate the call status, in addition to any result sets that might be returned by statements executed within the procedure. Because CALL can return multiple results, you should process them using a loop that calls mysql_next_result() to determine whether there are more results.

CLIENT_MULTI_RESULTS can be enabled when you call mysql_real_connect(), either explicitly by passing the CLIENT_MULTI_RESULTS flag itself, or implicitly by passing CLIENT_MULTI_STATEMENTS (which also enables CLIENT_MULTI_RESULTS). As of MySQL 5.5.3, CLIENT_MULTI_RESULTS is enabled by default.

If you enable CLIENT_MULTI_STATEMENTS or CLIENT_MULTI_RESULTS, you should process the result for every call to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 21.9.12, “C API Support for Multiple Statement Execution”.

For some parameters, it is possible to have the value taken from an option file rather than from an explicit value in the mysql_real_connect() call. To do this, call mysql_options() with the MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP option before calling mysql_real_connect(). Then, in the mysql_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_real_connect() call cannot be overridden in an option file, because the empty string indicates explicitly that the MySQL 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* 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.

Errors

Example 

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

By using mysql_options() the MySQL library reads the [client] and [your_prog_name] sections in the my.cnf file which ensures that your program works, even if someone has set up MySQL in some nonstandard way.

Note that upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1 in versions of the API older than 5.0.3, or 0 in newer versions. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up. You can use the MYSQL_OPT_RECONNECT option to mysql_options() to control reconnection behavior.


User Comments

Posted by Andrew Donkin on March 4 2005 2:23am[Delete] [Edit]

If you have configured your DNS to return a list of MySQL servers, and you want your client to work through that list until it finds one that works, you can put real_connect inside a getaddrinfo() loop. I wish the client library did it by itself:

struct addrinfo *addr, *addrlist;
struct addrinfo hints = {0, PF_UNSPEC, SOCK_STREAM,
0, 0, 0, 0, 0};

int gai_result = getaddrinfo(host, 0, &hints, &addrlist);
if (gai_result) bomb(Unknown host);

for (addr = addrlist; addr; addr = addr->ai_next) {
#define IPNAMELEN 20
char ipnamebuff[IPNAMELEN];
const char *ipname = inet_ntop(((struct sockaddr_in *) addr->ai_addr) ->sin_family,
(void *)&((struct sockaddr_in *) addr->ai_addr) ->sin_addr,
ipnamebuff, IPNAMELEN-1);

mysql_real_connect(mysql, ipname, user, pass, database, ...);
}

Posted by Brian Aker on May 15 2008 8:07pm[Delete] [Edit]

Andrew,

I believe this has been done, or will be done in 6.0.

Cheers,
-Brian

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