a text on optimizing C++

[Aurelien Gateau]

Alexander Neundorf wrote:

> especially http://www.goingware.com/tips/parameters/

This is a great resource. However, I fail to understand the following advice
(from http://goingware.com/tips/parameters/membervars.html): Given this
code example:

(--------------------------------------------
// User.cpp
#include "User.h"
User::User( const RefParam &inParam )
   : mPointerMember( new PointerMember( inParam ) )
{}
--------------------------------------------)

The authors writes:

(--------------------------------------------
Note that it is terribly important that you initialize pointer members
(actually any member) of your objects in the constructor's initialization
list.
[snip]
If you don't always need to have a pointer member in existence during the
lifetime of your object, you may choose to initialize it to nil [snip]. If
the pointer is going to need to be allocated before the constructor is
done, always do it in the initialization list, not in the body of the
constructor, like this:

User::User( const RefParam &inParam )
{
   mPointerMember = new PointerMember( inParam );  // DON'T DO THIS
   return;
}
--------------------------------------------)

Why is it bad to allocate a member in the constructor body?

Aurélien