HP aC++/HP C A.06.20 Programmer's Guide

Smaller Source Code
There are approximately 50 different algorithms and about a dozen major data
structures. This separation reduces the source code size, and decreases the risk of similar
activities with dissimilar interfaces. In the absense of this separation, each algorithm
must be implemented in each data structure. This requires additional member functions
apart from those in the present scheme.
Flexibility
The algorithms that are separated from data structures can be used with conventional
C++ pointers and arrays. Algorithms encapsulated within a class hierarchy do not have
this ability because C++ arrays are not objects.
Efficiency
The STL in particular, and the Standard C++ Library in general, provide a low-level
approach to develop C++ applications. This low-level approach is useful when specific
programs require an emphasis on efficient coding and execution speed.
Iterators: Mismatches and Invalidations
The Standard C++ Library data structures use pointer-like objects called iterators to
describe the contents of a container. Given the architecture of the library architecture,
it is impossible to verify whether the iterator elements are matched or derived from
the same container. Using a beginning iterator from one container with an ending
iterator from another produces unexpected results. It is very important to know that
iterators are invalidated as a result of a subsequent insertion or deletion from the
underlying container class. The use of an invalid iterator produces unexpected results.
Familiarity with the Standard C++ Library reduces the number of errors related to
iterators.
Templates: Errors and Code Bloat
The flexibility and power of templatized algorithms is, with most compilers, results in
a loss of precision in diagnostics. Errors in the parameter lists of generic algorithms is
sometimes displayed only as obscure compiler errors for internal functions. These
errors are defined many levels deep in template expansions. Familiarity with algorithms
and their requirements is necessary to use the standard library. Heavy reliance on
templates causes programs to grow larger than expected. You can minimize this problem
by recognizing the cost of instantiating a particular template class, and by making
appropriate design decisions. As compilers become more fluent in templates, the
problem of size is reduced.
Multithreading Problems
When you use the Standard C++ Library in a multithreaded environment, the iterators
cannot safely pass between threads. This is because iterators are independent of the
containers they operate on. It is impossible to protect a container when it spawns
Creating and Using Libraries 231