Using Strings or host-language Variables

Go Up to Using simple CONNECT Statements

Instead of using a database handle, CONNECT can use a database name supplied at run time. The database name can be supplied as either a host-language variable or a hard-coded, quoted string.

The following C code demonstrates how a program accessing only a single database might implement CONNECT using a file name solicited from a user at run time:

. . .
char fname[125];
. . .
printf('Enter the desired database name, including node
and path):\n');
gets(fname);
. . .
EXEC SQL
CONNECT :fname;
. . .

Tip:
This technique is especially useful for programs that are designed to work with many identically structured databases, one at a time, such as CAD/CAM or architectural databases.

Multiple Database Implementation

To use a database specified by the user as a host-language variable in a CONNECT statement in multi-database programs, follow these steps:

Declare a database handle using the following SET DATABASE syntax:
```
EXEC SQL
SET DATABASE handle = COMPILETIME 'dbname';
```
Here, <handle> is a hard-coded database handle supplied by the programmer, <dbname> is a quoted, hard-coded database name used by gpre during preprocessing.
Prompt the user for a database to open.
Store the database name entered by the user in a host-language variable.

Use the handle to open the database, associating the host-language variable with the handle using the following CONNECT syntax:

EXEC SQL
CONNECT :variable AS handle;

The following C code illustrates these steps:

. . .
char fname[125];
. . .
EXEC SQL
SET DATABASE DB1 = 'employee.ib';
printf("Enter the desired database name, including node
and path):\n");
gets(fname);
EXEC SQL
CONNECT :fname AS DB1;
. . .

In this example, SET DATABASE provides a hard-coded database file name for preprocessing with gpre. When a user runs the program, the database specified in the variable, fname, is used instead.

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Using a Hard-coded Database Names