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README-examples.md

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The libtabula Examples

libtabula ships with a large number of examples to show off all the many features of the library.

Building the Examples

If you're installing libtabula from the source tarball, the example programs get built when you build the library. If you change any example code, just say 'make' to rebuild the examples. The examples are built against the headers and library in the lib subdirectory, not against the ones you may have installed elsewhere on the system.

If these example files were installed on your system as part of the -devel RPM, copy all the files to a directory you can write to, then say 'make' in that directory. This uses a simplified Makefile, which builds the examples against the headers and libraries installed in the system directories.

Getting Started with the Examples

libtabula is built as a shared library on most systems, and a DLL on Windows. Since it isn't built in the same directory as the examples, this means that your system won't be able to find the library without help until you install it. Since you generally want to run the examples before installing the library, to test that the library actually works, we need a workaround.

That workaround is the exrun script. There are two versions, a Bourne shell script called just exrun for POSIX systems, and exrun.bat for Windows.

Before running the other examples, you must first create the sample database. On POSIX systems, you do that like so:

$ ./exrun resetdb [-s server_addr] [-u user] [-p password]

On Windows, that would instead be:

C:\libtabula> exrun.bat resetdb [-s server] [-u user] [-p pass]

You don't have to give any of these options. If you don't pass -s, it assumes the database server is running on the same machine, and so tries to contact the server over some form of local IPC. If you don't pass -u, it uses your own user name when logging into to the database server. If you don't pass -p, it assumes the database user has an empty password, which hopefully is not true.

The -s option accepts many different forms of address. The main one is some sort of TCP/IP address, with an optional port number or service name. On Unixy systems, you can give a Unix domain socket name. On Windows, you can give just a period to use named pipes, if the server supports it. All of these are legal:

  • .
  • localhost
  • 172.20.0.252:12345
  • /var/run/mysqld.sock
  • my.server.name.com:mysql

If you give -s but don't give a port number or service name with it, it assumes the default, port 3306.

Running the Other Command Line Examples

The following examples use the database set up by resetdb, and have the same command line format as resetdb:

  • simple1: Shows the item names for all records in the sample stock table. Try this one if you do nothing else.

  • simple2: Similar to simple1, but it displays all columns from the sample stock table, not just the item name.

  • simple3: Same as simple2, except that it retrieves the data with a use query instead of a store query. See the user manual for the difference between these methods.

  • ssqls1-5: These demonstrate the SSQLS features. Read the SSQLS sections in the user manual for details about these examples.

  • multiquery: libtabula allows you to issue multiple queries at once, and get the results as separate sets. This shows that, and also how to use stored procedures, which return their results in the same way as a multiquery.

  • tquery1-3: Shows how to use the template query facility.

  • transaction: Shows how to use the Transaction class to create transaction sets which automatically roll back if not explicitly committed.

  • deadlock: Shows how to handle errors that happen when the database server detects a deadlock in a transaction set. Also demonstrates the need for BadQuery::errnum()

  • store_if: Demonstrates the Query::store_if() method, which allows you to store the results of a query in an STL container conditionally. Think of it as a way to express rules for selecting records in C++, to be used when SQL's WHERE clause isn't powerful enough.

  • for_each: Demonstrates the Query::for_each() method, which allows you to execute a query and call a functor on each returned row. This example uses this to gather statistics on the sample table's contents.

  • cpoolp, cpoolw: Respectively, the POSIX and Windows threads variants of the ConnectionPool class demonstration.

  • load_jpeg: Inserts a JPEG file into the sample database, for use by the cgi_jpeg example. (See below.) Unlike the other examples, this one takes anything given on the command line that isn't a switch to be a JPEG file name. We've included examples/logo.jpg as a sample, if you want to use that.

  • fieldinf: Shows how to get information about the fields in a result set. (Types, etc.)

  • dbinfo: Dumps a bunch of information about the database server and some of the data it's managing.

If you run the load_jpeg example, you should consider also playing with the other half of the demonstration, cgi_jpeg. To run it, you'll need to install libtabula and cgi_jpeg on a machine with a web server and a database server. Copy the cgi_jpeg program to the server's CGI directory. For example, on a stock Red Hat type box, that would be /var/www/cgi-bin. At that point, a request like http://my.server.com/cgi-bin/cgi_jpeg?id=1 should show the JPEG you loaded. The ID value to use will be that reported by load_jpeg.

Dedicated Windows Examples

If you're a Visual C++ user, there are two GUI examples, too:

  • examples\vstudio\mfc.vcproj: MFC-based replacement for the simple2 example.

  • examples\vstudio\wforms.vcproj: The same thing, only written in C++/CLI and using Windows Forms. Please follow the instructions in the Visual C++ README before trying to build and run this example. The libtabula library build settings must be modified and the library rebuilt first.

Although these examples show use of libtabula in a GUI rather than command line program, that's not the main point of these examples. What we're really showing here is how to deal with Unicode. Most DBMSes supported by libtabula natively use the UTF-8 encoding for Unicode, which works naturally with on non-Windows systems. Windows, on the other hand, uses a different Unicode character encoding, UTF-16. These examples show how to do the necessary conversions. (See the Unicode chapter in the user manual for more on this topic.)

We need two different examples because Unicode conversions and string handling are so wildly different under .NET than with the native Win32 API. .NET makes these tasks much easier.

These examples build and run as-is under Visual C++ 2005. To make them work with VC++ 2008, you will have to change several paths in both project's settings to reference the vc2008 subdirectory instead of vc2005:

  • Configuration Properties > Debugging > Working Directory

  • Configuration Properties > Linker > General > Additional Library Directories

If you want to backport these examples to VC++ 2003, it's probably not hard. The main difficulty is that VS 2003 supports Managed C++, which isn't the same thing as C++/CLI.

Special exrun Capabilities

The Bourne shell version of the exrun script has a few features not avaiable in the Windows batch file version, exrun.bat. These features let you run the examples under various debugging tools.

You can get simple gdb debugging if you run an example like this:

$ ./exrun gdb simple1 foo bar qux

The script also supports valgrind, in memory leak testing mode:

$ ./exrun valgrind simple1 foo bar qux