473,883 Members | 1,668 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

Assigning NULL to a variable (not pointer)

I remember that this is a bad practice, but can not find a definitive
resource that states it is bad and why. Can anyone help?

Oct 16 '06
31 17720
"Ron Natalie" <ro*@spamcop.ne twrote in message
news:45******** **************@ news.newshostin g.com...
Jim Langston wrote:
int MyVar = NULL;

I would immediatly presume that MyVar is being cast to a pointer
somewhere and is not acutally used as an integer. And I would start
reading the code with that in mind.

There's no guarantee that a int reinterpret_cas ted to a pointer yields
a null pointer value. You get only two guarantees:

1. A integer constant expression of value zero converts to a null

2. A pointer value can be converted to a sufficiently large integer
(if such exists) and back to the original pointer type without
I agree to that, yet I still see unsigned long ints used as pointers in some
code written for Windows.
Oct 17 '06 #31
Jim Langston wrote:
I agree to that, yet I still see unsigned long ints used as pointers in some
code written for Windows.

Windows has a type for that actually. They call it DWORD_PTR
which took me a while to realize it isn't a poitner to a DWORD
but a integral type that's big enough to hold either a DWORD
or a pointer. Microsoft had to chase down these when they
went to x64 because they were using DWORD (32 bits) to hold
pointers all over the place in the hideous windows message system.
Oct 17 '06 #32

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

by: fix | last post by:
Hi all, I am new to C and I just started to program for a homework. I included my code down there. It is a fraction "class". I declared the Fraction struct, tried to create some invalid fraction, with denominator zero. A Fraction is created by the newFraction() function, and which in turns call normalize() function to simplify it, but before, the normalize() function will do a check, if the denominator is zero, it will give a error by...
by: junky_fellow | last post by:
Can 0x0 be a valid virtual address in the address space of an application ? If it is valid, then the location pointed by a NULL pointer is also valid and application should not receive "SIGSEGV" ( i am talking of unix machine ) while trying to read that location. Then how can i distinguish between a NULL pointer and an invalid location ? Is this essential that NULL pointer should not point to any of the location in the virtual address...
by: Jason Curl | last post by:
I've been reading this newsgroup for some time and now I am thoroughly confused over what NULL means. I've read a NULL pointer is zero (or zero typecast as a void pointer), others say it's compiler dependent (and that NULL might be anything, but it is always NULL). The source snippet is below. The question is: - When I use calloc to allocate a block of memory, preinitialising it to zero, is this equivalent (and portable C) to...
by: Mikhail Teterin | last post by:
Hello! Consider the following simple accessor function: typedef struct { int i; char name; } MY_TYPE; const char *
by: weston | last post by:
I've got a piece of code where, for all the world, it looks like this fails in IE 6: hometab = document.getElementById('hometab'); but this succeeds: hometabemt = document.getElementById('hometab'); Has anyone ever seen anything like this before, or am I dreaming?
by: I.M. !Knuth | last post by:
Hi. I'm more-or-less a C newbie. I thought I had pointers under control until I started goofing around with this: ================================================================================ /* A function that returns a pointer-of-arrays to the calling function. */ #include <stdio.h> int *pfunc(void);
by: Sourav | last post by:
Suppose I have a code like this, #include <stdio.h> int *p; void foo(int); int main(void){ foo(3); printf("%p %d\n",p,*p);
by: Donos | last post by:
Hello I have the following program, void getValue(unsigned char* pVal) { pVal = allValues(); } unsigned char* allValues()
by: emyl | last post by:
Hi all, here's an elementary question. Assume I have declared two variables, char *a, **b; I can then give a value to a like a="hello world";
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
by: Oralloy | last post by:
Hello folks, I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>". The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed. This is as boiled down as I can make it. Here is my compilation command: g++-12 -std=c++20 -Wnarrowing bit_field.cpp Here is the code in...
by: Hystou | last post by:
Overview: Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
by: tracyyun | last post by:
Dear forum friends, With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules. He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms. Adolph will...
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.