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mysql database server

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How do I write a C program to connect MySQL database server?

MySQL database does support C program API just like PHP or perl.

The C API code is distributed with MySQL. It is included in the mysqlclient library and allows C programs to access a database.

Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients. You can find these in the clients directory in the MySQL source distribution.

Requirements

Make sure you have development environment installed such as gcc, mysql development package etc. Following is the list summarize the list of packages to compile program:

  • mysql: MySQL client programs and shared library
  • mysqlclient: Backlevel MySQL shared libraries (old libs)
  • mysql-devel: Files for development of MySQL applications (a must have)
  • mysql-server: Mysql server itself
  • gcc, make and other development libs: GNU C compiler

Sample C Program

Following instructions should work on any Linux distro or UNIX computer. Here is the small program that connects to mysql server and list tables from mysql database.(download link):

/* Simple C program that connects to MySQL Database server*/
#include <mysql.h>
#include <stdio.h>
main() {
   MYSQL *conn;
   MYSQL_RES *res;
   MYSQL_ROW row;
   char *server = "localhost";
   char *user = "root";
   char *password = "PASSWORD"; /* set me first */
   char *database = "mysql";
   conn = mysql_init(NULL);
   /* Connect to database */
   if (!mysql_real_connect(conn, server,
         user, password, database, 0, NULL, 0)) {
      fprintf(stderr, "%s\n", mysql_error(conn));
      exit(1);
   }
   /* send SQL query */
   if (mysql_query(conn, "show tables")) {
      fprintf(stderr, "%s\n", mysql_error(conn));
      exit(1);
   }
   res = mysql_use_result(conn);
   /* output table name */
   printf("MySQL Tables in mysql database:\n");
   while ((row = mysql_fetch_row(res)) != NULL)
      printf("%s \n", row[0]);
   /* close connection */
   mysql_free_result(res);
   mysql_close(conn);
}

How do I compile and link program against MySQL libs?

MySQL comes with a special script called mysql_config. It provides you with useful information for compiling your MySQL client and connecting it to MySQL database server. You need to use following two options.
Pass --libs option - Libraries and options required to link with the MySQL client library.

$ mysql_config --libs
Output:

-L/usr/lib64/mysql -lmysqlclient -lz -lcrypt -lnsl -lm -L/usr/lib64 -lssl -lcrypto

Pass --cflags option - Compiler flags to find include files and critical compiler flags and defines used when compiling the libmysqlclient library.
$ mysql_config --cflags
Output:

-I/usr/include/mysql -g -pipe -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -fno-strict-aliasing

You need to pass above option to GNU C compiler i.e. gcc. So to compile above program, enter:
$ gcc -o output-file $(mysql_config --cflags) mysql-c-api.c $(mysql_config --libs)
Now execute program:
$ ./output-file
Output:

MySQL Tables in mysql database:
columns_priv
db
func
help_category
help_keyword
help_relation
help_topic
host
tables_priv
time_zone
time_zone_leap_second
time_zone_name
time_zone_transition
time_zone_transition_type
user 

References:

  • MySQL C API - A must read - official MySQL C API documentation

By default remote access to the MySQL database server is disabled for security reasons. However, some time you need to provide remote access to database server from home or a web server. This post will explain how to setup a user account and access a mysql server remotely on a Linux or Unix-like systems.
[click to continue…]

MySQL is popular for web applications and acts as the database component of the LAMP, MAMP, and WAMP platforms. Its popularity as a web application is closely tied to the popularity of PHP, which is often combined with MySQL.

MySQL is open source database server and by default it listen on TCP port 3306.

Task: Open port 3306

In most cases following simple rule opens TCP port 3306:
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 3306 -j ACCEPT

Following iptable
rules allows incoming client request (open port 3306) for server IP address 202.54.1.20. Add rules to your iptables shell script:

iptables -A INPUT -p tcp -s 0/0 --sport 1024:65535 -d 202.54.1.20 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT-p tcp -s 202.54.1.20 --sport 3306 -d 0/0 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT

However in real life you do not wish give access to everyone. For example in web hosting company, you need to gives access to MySQL database server from web server only. Following example allows MySQL database server access (202.54.1.20) from Apache web server (202.54.1.50) only:

iptables -A INPUT -p tcp -s 202.54.1.50 --sport 1024:65535 -d 202.54.1.20 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s 202.54.1.20 --sport 3306 -d 202.54.1.50 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT

Please note if you follow above setup, then you need tell all your hosting customer to use 202.54.1.50 as MySQL host in PHP/Perl code. A better approach is to create following entry in /etc/hosts file or use fully qualified domain name (create dns entry) mysql.hostingservicecompany.com which points to 202.54.1.50 ip:
202.54.1.50 mysql

In shot MySQL database connection code from PHP hosted on our separate webserver would look like as follows:

// ** MySQL settings ** //
define('DB_NAME', 'YOUR-DATABASE-NAME');     // The name of the database
define('DB_USER', 'YOUR-USER-NAME');     // Your MySQL username
define('DB_PASSWORD', 'YOUR-PASSWORD''); // ...and password
define('DB_HOST', 'mysql'); 
// ** rest of PHP code ** //

Task: Allow outgoing MySQL request on TCP port 3306

Even you can allow outgoing MySql client request (made via mysql command line client or perl/php script), from firewall host 202.54.1.20:

iptables -A OUTPUT -p tcp -s 202.54.1.20 --sport 1024:65535 -d 0/0 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s 0/0 --sport 3306 -d 202.54.1.20 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT