HP aC++/HP C A.06.28 Programmer's Guide Integrity servers (769150-001, March 2014)

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 iterators in multiple threads as iterators
are used to modify a non-const container. Use thread-safe wrappers, such as those provided by
Tools.h++ Library to access a container from multiple threads.
Standard C++ Library Reference
The Standard C++ Library Reference provides an alphabetical listing of all of the classes, algorithms,
and function objects in the prior Rogue Wave implementation of the Standard C++ Library.
Incompatibilities Between the Library and the Standard
The ANSI/ISO C++ International Standard is different from Standard C++ Library. For example,
the times function object in the functional header file. In the standard, times is renamed to
multiplies.
To use multiplies in your code and to be compatible with the ANSI/ISO C++ International
Standard, use a conditional compilation flag on the aCC command line.
Example:
178 Tools and Libraries