2. Using Libann in your Programs

There are no special features that you need to know about when using Libann, that don't also apply to other C++ libraries. However, the effects of ignoring them might be more severe than with simpler programs. This chapter is largely a memorandum for persons not thoroughly familiar with C++ programming. If you're an expert with C++, then you can skip this chapter, or just give it a cursory glance.

2.1 Namespaces		Avoiding identifier clashes.
2.2 Public Header Files		Declarations you need to know about.
2.3 Exceptions		Exceptional situations.
2.4 Randomness
2.5 Compiling and Linking with Libann		How to produce an executable.

2.1 Namespaces

• Prepend every typename and classname with ann::; or
• Put the statement using namespace ann; at the start of every file.

If you don't do one of these, then your compiler won't recognise any identifiers from the library. This is a feature designed to prevent clashes with symbols from other libraries or from other parts of your own program.

2.2 Public Header Files

#include <ann/mlp.h>

As well as a header file for each network type, there is a common file, `ann/ann.h' which contains declarations for classes which you'll almost definitely need if you're going to do anything useful with Libann. More about this header file later.

2.3 Exceptions

This is not to say that all exceptions are errors. Exceptions should be thought of as exactly what their name suggests, viz: things which happen only in exceptional circumstances. For example you might know that most of your vectors are the appropriate size for a network, but that there are the occasional few which are not. In that case, you could catch the exception and deal with the few cases as they arise.

The potential to throw exceptions however, means that you must protect your main function with a try-catch block:

#include <stdexcept> #include <iostream> int main(int argc, char **argv) { try { // Program will go here return 0; } catch (const std::exception &e) { std::cerr << "Unexpected exception " << e.what() << std::endl; } catch (...) { std::cerr << "Unhandled exception\n"; } return 1; }

There is nothing new here. Any C++ program should have this (or something similar) in its main. You might not think you need to be worried about exceptions, but you do (use of the new operator has the potential to throw an exception). If you don't catch exceptions like this, then your program may unexpectedly terminate and you'll have no idea why.

2.4 Randomness

Therefore, before using Libann, your program should make a call to srand() to initialise the random generator seed. Whilst developing and debugging, it's useful to use the same seed each time. Simply calling srand(0) is the easiest way to do this. When your program is complete however, you should ensure that the generator is truly random. One way to do this, is to initialise the seed from the real time clock:

#include <stdlib.h> #include <time.h> int main() { srand(time(0)); . . . return 0; }

2.5 Compiling and Linking with Libann

g++ -I /usr/local/libann/include -lann -L /usr/local/libann prog.cc