Member initialization list question

Hi,

Where is the proper place to use a member initialization list, the
header or cpp file?

Does it make any difference?

Also, is there any difference between using a member initialization list
and initializaing member variables in the constructor?

i.e.

MyClass(void) : a(1), b(2) {};

vs

MyClass::MyClass(void)
{
a = 1;
b = 2;
}

Thanks B

re: Member initialization list question

Bryan <spam@nospam.comwrote in news:06aph.43401$wc5.41974
@newssvr25.news.prodigy.net:
Wherever you're defining your constructor.
Yes, probably. But that's only because member bodies which are defined
directly within the definition of a class are implicitly marked as
inlined functions (reminder: inline is only a hint to the compiler, the
compiler is not required to respect the hint).
listYes. See the FAQ, section 10.6 (http://www.parashift.com/c++-faq-
lite/ctors.html#faq-10.6)

re: Member initialization list question

Bryan wrote:The initialisation list is part of the definition of the constructor.
If the constructor definition is in the header, that is where the
initialisation list will be. If the constructor definition is in the
implementation file, that is where the initialisation list will be. Do
you usually put your constructor definitions in the header or the
implementation file? Or does it depend?
Using an initialisation list is the only way you can initialise members
in a constructor.
The difference is that the latter is NOT initialisation. It is
assignment.
http://www.parashift.com/c++-faq-lit....html#faq-10.6

Gavin Deane

re: Member initialization list question

Bryan wrote:This initializes the variables a and b.This assigns values to a and b after they are (unfortunately in this
case) not initialized.

It's entirely analogous to:

int a(1);
and
int a;
a = 1;

re: Member initialization list question

Bryan wrote:The language syntax requires the init list to go with the definition of
the constructor.
Delete the semicolon. Delete void -- it's a C-ism.Delete void -- It's a C-ism.Yes. the first case directly constructs a and b. The second case
default constructs a and b, and then assigns them. If members are
expensive to construct and assign, you may see a performance hit (but
only worry about that *AFTER BENCHMARKING*), and the second case will
also fail if either a or b is a const member.

re: Member initialization list question

Unfortunately, it doesn't default construct a and b. It doesn't
even default initialize them in many cases.