Connecting to a Datasource
First thing you will need is a variable of type `SQLHENV`. This is a handle (pointer) to an internal ODBC structure which holds all informationen about the ODBC environment. Without a handle of that kind you won't be able do to very much. To get this handle you call `SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &V_OD_Env)`. `V_OD_Erg` is a variable of type `SQLHENV` which holds the allocated environment handle. If you have allocated the handle you need to define which version of ODBC to use. Therefore you should call `SQLSetEnvAttr(V_OD_Env, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0)`. The constant `SQL_ATTR_ODBC_VERSION` defines that the needed version of ODBC will be defined and `SQL_OV_ODBC3` says that the program will need ODBC 3.0. Next thing to do is to create a handle for the database connection which is of the type `SQLHDBC`. Once again you call `SQLAllocHandle` this time with `SQL_HANDLE_DBC` and the variable to the environment returned by the first call to `SQLAllocHandle`. Then you may choose to modify the connection attributes, mainly the timeout for any given action on the connection. You do this by calling `SQLSetConnectAttr` with the connection handle, attribute and value pointer and the string length (if available). Finally we are able to connect to the database via `SQLConnect`, which needs the name of the data source, the username and password as parameters. For each parameter you need to specify how long the string is or just gib `SQL_NTS` which says that it is a string which length has to be determined by `SQLConnect` That's it, we are connected to the database. Please note, that all functions mentioned on this page return either `SQL_SUCCESS`, `SQL_SUCCESS_WITH_INFO` if all went smoothly or `SQL_ERROR` or `SQL_INVALID_HANDLE` in case of an error. We will have a look on how to get diagnostic messages a little later. So let's have a look at the code:

    /* odbc.c

        testing unixODBC
    */
    #include <stdlib.h>
    #include <stdio.h>
    #include <odbc/sql.h>
    #include <odbc/sqlext.h>
    #include <odbc/sqltypes.h>

    SQLHENV			 V_OD_Env;     // Handle ODBC environment
    long			 V_OD_erg;     // result of functions
    SQLHDBC			 V_OD_hdbc;    // Handle connection

    char			 V_OD_stat[10]; // Status SQL
    SQLINTEGER		 V_OD_err,V_OD_rowanz,V_OD_id;
    SQLSMALLINT		 V_OD_mlen;
    char             V_OD_msg[200],V_OD_buffer[200];

    int main(int argc,char *argv[])
    {
    	// 1. allocate Environment handle and register version
    	V_OD_erg=SQLAllocHandle(SQL_HANDLE_ENV,SQL_NULL_HANDLE,&V_OD_Env);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error AllocHandle\n");
    		exit(0);
    	}
    	V_OD_erg=SQLSetEnvAttr(V_OD_Env, SQL_ATTR_ODBC_VERSION,
                                   (void*)SQL_OV_ODBC3, 0);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error SetEnv\n");
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
    	// 2. allocate connection handle, set timeout
    	V_OD_erg = SQLAllocHandle(SQL_HANDLE_DBC, V_OD_Env, &V_OD_hdbc);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error AllocHDB %d\n",V_OD_erg);
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
    	SQLSetConnectAttr(V_OD_hdbc, SQL_LOGIN_TIMEOUT, (SQLPOINTER *)5, 0);
    	// 3. Connect to the datasource "web"
    	V_OD_erg = SQLConnect(V_OD_hdbc, (SQLCHAR*) "web", SQL_NTS,
                                         (SQLCHAR*) "christa", SQL_NTS,
                                         (SQLCHAR*) "", SQL_NTS);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error SQLConnect %d\n",V_OD_erg);
    		SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1,
    		              V_OD_stat, &V_OD_err,V_OD_msg,100,&V_OD_mlen);
    		printf("%s (%d)\n",V_OD_msg,V_OD_err);
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
    	printf("Connected !\n");
    	/* continued on next page */