CSCE 121 Chapter 5

« previous | Monday, September 6, 2010 | next »

Philosophy of Program Correctiveness

A program should:

1. produce desired results for all legal inputs
2. give reasonable error messages for all illegal inputs
3. not worry about malfunctioning hardware or other software
4. be allowed to terminate upon finding an error

Exceptions

void error(string msg) {
  throw runtime_error(msg);
}
...
int main()
try {
  ... // if something calls error() function, then catch will run.
} catch (runtime_error& e) {
  cerr << "runtime_error: " << e.what() << endl;
  return 1;
}

• & after exception type declaration means "pass the exception by reference"
• cerr is just like cout, except it's used for error messages.

To catch ALL exceptions, use the following code:

try {
  ...
} catch (exception& e) {
  cerr << "error: " << e.what() << endl;
}

• exception is the generic exception class

Wednesday, September 8, 2010

Code Structure

• Comments/documentation
• meaningful names
• Indentation
• Small functions
• Use libraries where available

Debugging

• test as often as necessary
• don't "quick-fix"

Logically structuring functions can eliminate bugs in the future:

Pre-conditions

Think: What does a function require of its arguments?

Check them at beginning of function before using them

Post-conditions

sanity-check for return values (e.g. check for negative area)

Testing

Try to break your own application. Be as stupid as possible to simulate every type of error imaginable.