2.4 Exceptions

Detects
try
{ //code that may raise an exception and/or set some condition
if (condition)
throw exceptionName;
//Freq. A string
}

Handles
Catch (exceptionType variable)
{ //code handles
}
//code to continue processing
//executed unless catch block stops processing with halt; or return
Example
…
try
{ infile >> value;
if (value < 0 )
throw string (“Negative value”);
y = sqrt (value);
}
catch (string message )
{ //code handles
cout << message << “found in file. Abort.”;
return –1
}
//code to continue if exception not thrown
cout << “sqrt of “ << value << “is “ << y << endl;
Types to throw and catch
– for messages
 ints – to use in a case to handle different
reasons exception thrown
 strings
Specifying Functions
Up to now Purpose/Receives/Returns
 Text Book uses Pre- and Post-conditions
 Pre-condition: describes what must be true
about the state for the function to work
correctly
 Post-condition: describes what will be true
about the state if the pre-conditions are met

Specifying Functions cont.
– discusses appropriate
values for receives parameters and
member data of object if it is a member
function we are specifying
 Post-condition – describes what the
return variables values will be and what
changes will be made to the object
 Precondition
Error Conditions
Describe what preconditions will be checked
by the function (might use try/catch)
Primary vs Enhanced Operations

Primary -Member
functions
–
–
Constructor
Transformers



–
Observers


–
Change 1 piece of ADT
Add 1 piece to ADT
Delete 1 piece of ADT
Accessors – look at 1
piece of ADT
Predicates – return a bool
value regarding state of
ADT
Destructor

Enhanced - Non-member
functions
– manipulate many pieces of
ADT (iterators)
– manipulate several pieces of
ADT
– Manipulate several
instances of same type of
ADT
– Call primary operations to
get work done
#ifndef
#ifndef FILE_H
 #define FILE_H


#endif