C++ for Scientists - Technische Universität Dresden

2.8. STRUCTURING SOFTWARE PROJECTS 47
#include
#include
int main () {
std::ofstream myfile(”example.txt”);
myfile ≪ ”Writing this to a file. ” ≪ std::endl;
return 0;
}
2.8 Structuring Software Projects
2.8.1 Namespaces
In the last section we mentioned that equal names in different scopes hides the variables (or
functions, types, . . . ) of the outer scopes while defining the same name in one scope is an error.
Common function names like min, max or abs already exists and if you write a function with
the same name (and same argument types) the compiler will tell you that the name already
exists. But this does not only concern common names; you must be sure that every name you
use is not already used in some other library. This really can be a hustle because you might
add more libraries later and there is new potential for conflicts. Then you have to rename some
of your functions and inform everybody who uses your software. Or one of your software users
is including a library that you do not know and has a name conflict. This can grow to a serious
problem and it happens in C all the time.
One possibility to deal with this is using different names like max , my abs, or library name abs.
This in fact what is done in C. Main libraries have short function names, user-libraries longer
names, and OS-related internals typically start with . This decreases the probability of conflicts
but does not eliminate it entirely.
Remark: Particularly annoying are macros. This is an old technique of code reuse by expanding
macro names to their text definition, potentially with arguments. This gives a lot of possibilities
to empower your program but much more for ruin it. Macros are resistent against namespaces
because they are reckless text substitution without any notion of types, scopes or any other
language feature. Unfortunately, some libraries define macros with common names like major.
We uncompromisingly undefine such macros, e.g. #undef major, without merci for people that
might want use those macros. Visual Studio defines — till today!!! — min and max as macros
and we advise you to disable this by compiling with /DNO MIN MAX. Almost all macros can be
replaced by other techniques (constants, templates, inline functions). But if you really do not
find another way of implementing it use LONG AND UGLY NAMES IN CAPITALS like the library
collection Boost does.
2.8.2 Header and implementation
It is usual to split class (Chapter 3) and function definition and implementation into different
files. Classes and functions are typically defined in a header file (.hpp), and implemented in a
cpp file, which is then compiled and added to a library. For example, the header file foo.hpp
could be:
foo.hpp: