Solved

What is the Compiler Doing?

Posted on 2000-02-25
2
201 Views
Last Modified: 2010-08-05
I am using VC++ 6.0.  What happens when a file such as #include<iostream> is inserted into several different files all within the same project?  Obviously, it is not necessary to include a file more than once but it seems to be done quite often.   Does this hinder the performance of the executable?  What exactly is happening?  Just wondering...
0
Comment
Question by:guile1
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
2 Comments
 
LVL 1

Accepted Solution

by:
Binder earned 100 total points
ID: 2559000
  No, it don´t hinder the performance of the executable, just
the performance of the compiler (a little bit). But there is a way
to minimize this effect. Looking at the start of iostream.h we found:

#ifndef _INC_IOSTREAM
#define _INC_IOSTREAM

....
#endif

   and of course several other lines of code. This means that
if the file wasn´t already included (if the symbol  _INC_IOSTREAM
wasn't defined yet) then the compiler includes it. If the symbol
was already defined, the compiler didn´t include it again.
0
 
LVL 22

Expert Comment

by:nietod
ID: 2559096
The use of #ifdef in that maner is very common.  It is necessary because C/C++ has rules against multiple definitions of the same "thing" in the same translation unit.  Without those #ifdef guards, the code would probably not compile.
0

Featured Post

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article shows you how to optimize memory allocations in C++ using placement new. Applicable especially to usecases dealing with creation of large number of objects. A brief on problem: Lets take example problem for simplicity: - I have a G…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

752 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question