Cons:
Nonmember and static member functions may make more sense as
members of a new class, especially if they access external resources or have
significant dependencies.
Decision:
Sometimes it is useful, or even necessary, to define a function not bound to a
class instance. Such a function can be either a static member or a nonmember
function. Nonmember functions should not depend on external variables, and
should nearly always exist in a namespace. Rather than creating classes only to
group static member functions which do not share static data, use namespaces
instead.
Functions defined in the same compilation unit as production classes may
introduce unnecessary coupling and link-time dependencies when directly called
from other compilation units; static member functions are particularly susceptible
to this. Consider extracting a new class, or placing the functions in a namespace
possibly in a separate library.
If you must define a nonmember function and it is only needed in its
.cc
file, use
an unnamed namespace
or
static
linkage (eg
static int Foo() {...}
) to
limit its scope.
Local Variables
▽
Place a function's variables in the narrowest scope possible, and initialize
variables in the declaration.
LINK
C++ allows you to declare variables anywhere in a function. We encourage you
to declare them in as local a scope as possible, and as close to the first use as
possible. This makes it easier for the reader to find the declaration and see what
type the variable is and what it was initialized to. In particular, initialization
should be used instead of declaration and assignment, e.g.
int i;
i = f(); // Bad -- initialization separate from declaration.
int j = g(); // Good -- declaration has initialization.
Note that gcc implements
for (int i = 0; i < 10; ++i)
correctly (the
scope of
i
is only the scope of the
for
loop), so you can then reuse
i
in
another
for
loop in the same scope. It also correctly scopes declarations in
if
and
while
statements, e.g.
while (const char* p = strchr(str, '/')) str = p + 1;
There is one caveat: if the variable is an object, its constructor is invoked every
time it enters scope and is created, and its destructor is invoked every time it
goes out of scope.
// Inefficient implementation:
for (int i = 0; i < 1000000; ++i) {
Foo f; // My ctor and dtor get called 1000000 times each.
f.DoSomething(i);
}
It may be more efficient to declare such a variable used in a loop outside that
loop:
Foo f; // My ctor and dtor get called once each.
11/05/2010 Google C++ Style Guide
…googlecode.com/svn/…/cppguide.xml 9/50
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