A couple questions regarding C++, C, MFC

Question

1.20/5 (5 votes)

See more:

Please explain these to me:
1. Difference between void pointer and Null pointer.
2. Why Null pointer is necessary?
3. Difference between malloc() and calloc().
4. Purpose of "extern" keyword

Thanks in advance!

Posted 30-Mar-11 3:16am

UL UL ALBAB

Updated 30-Mar-11 3:22am

Manfred Rudolf Bihy

v4

Add a Solution

Comments

Manfred Rudolf Bihy 30-Mar-11 9:22am

You've not by any chance had an interview today?

Olivier Levrey 30-Mar-11 9:34am

My vote of 2. How many questions are you going to ask on all C/C++ basics???
Go ahead, search the web, read books!

Sandeep Mewara 30-Mar-11 9:35am

No effort.

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

CPallini · Accepted Answer · 2011-03-30T04:05:00

Solution 3

(1) void is a type, NULL is a value.
(2) Why the empty set is necessary in set theory?
(3) calloc initializes (with zeroes) allocated memory while malloc doesn't.
(4) extern is used:
- to declare a variable defined in another source file (e.g. extern int g_instance_count; ).
- to notify the C++ compiler that some code is C (e.g. extern "C" {/* C functions here */ }).

Posted 30-Mar-11 4:05am

CPallini

Updated 30-Mar-11 10:46am

v3

Comments

Sergey Alexandrovich Kryukov 30-Mar-11 16:36pm

Of course, this Answer is too advanced to the one who voted "3".
I think this Answer is excellent; I especially like (2).
5++++++
--SA

CPallini 30-Mar-11 16:47pm

I should know that. Thank you, sir. :-)

Sergey Alexandrovich Kryukov 30-Mar-11 16:36pm

Recommended as Answer. It's the best one so far.
--SA

Stephen Hewitt · Accepted Answer · 2011-03-30T03:26:00

Solution 1

1. Difference between void pointer and Null pointer.
void* is a type of pointer but NULL is a value that any pointer can assume.

2. Why Null pointer is necessary?
NULL is normally used to indicate that the pointer doesn't point to anything.

Posted 30-Mar-11 3:26am

Stephen Hewitt

ganesh_IT · Accepted Answer · 2011-03-30T03:32:00

Solution 2

extern key word is used to provide linkage.

Posted 30-Mar-11 3:32am

ganesh_IT

Comments

UL UL ALBAB 30-Mar-11 10:00am

I need example...