But the idea of mentioning the above snippet is that we should always check for NULL before accessing it. As per C11 standard clause 6. Even C11 clause 6. On gcc, the above would output 1.
Here C11 has mentioned guidelines. From clause 6. Inspite of mentioning machine dependent stuff as above, we as C programmers should always strive to make our code as portable as possible. So we can conclude on NULL as follows:. Always initialize pointer variables as NULL. Always perform NULL check before accessing any pointer. Also, please do leave us comment for further clarification or info. This article is attributed to GeeksforGeeks. Prev Next.
More topics on C Programming. Well, usage of sizeof NULL is allowed but the exact size would depend on platform. If the pointer size of a platform is 4 bytes, the output of the above program would be 4. But if pointer size on a platform is 8 bytes, the output of the above program would be 8. Skip to content. Change Language. Related Articles.
Table of Contents. Improve Article. Save Article. Like Article. The example of a is. Take a step-up from those "Hello World" programs. Learn to implement data structures like Heap, Stacks, Linked List and many more! Mark: Consistency is always the most important factor of your style. I don't agree with the statement above that consistency is what matters. This has nothing to do with consistency; not the Good sort anyway. This is the area where we should let programmers express their own style.
If there's a person that doesn't immediately understand either form then they should stop reading code right away and consider a career change. I'll say more than that: If there's a cosmetics consistency you can't automatically enforce with a script then remove it.
The cost of draining human moral is WAY more important than those stupid decisions people make in a meeting. Show 9 more comments. Active Oldest Votes. Improve this answer.
RBerteig RBerteig One important thing to note: until recently, I was in favor of writing "if ptr " instead of "if ptr! But I just found out that comparison raises resp. So if you want to check a pointer, better to do "if ptr! It is always a null pointer constant though. It can never evaluate to true. The expression! Show 3 more comments. Use it. Add a comment. In C C is a different beast. Deduplicator M2tM M2tM 4, 32 32 silver badges 41 41 bronze badges. You said 0 is preferable, but NULL must be zero.
This is a good point, I neglected to mention it and I'm improving my answer by suggesting it. Show 2 more comments. I use if ptr , but this is completely not worth arguing about. One comment, though: If you plan to recognize the error and not continue executing the function i. It could work or not. Mark Ransom Mark Ransom k 40 40 gold badges silver badges bronze badges. But I suppose a good naming convention makes this argument moot.
Daniel Hershcovich Daniel Hershcovich 3, 2 2 gold badges 27 27 silver badges 35 35 bronze badges. If the reader is so lost about levels of indirection, I'm not sure he isn't a safety-hazard as a programmer. Peter Mortensen Derek Derek They never use this style themselves. Settle down, folks. They are obviously less famous as their initials aren't even capitalized. Actually, I use both variants. I know this can lead to the discussion "should a function have only one exit point" Most of the time, you check the pointer, then do what you want and then resolve the error case.
I personally hate the arrow code that would result using one exit point. Why don't exit if I already know the answer? Also in many cases a malloc that would need cleanup could be replaced by a faster alloca. If it fails, your program just blows up.
There is no chance for recovery, and since the stack is relatively small, failure is likely. On failure, it's possible that you clobber the heap and introduce privilege-compromising vulnerabilities. Never use alloca or vlas unless you have a tiny bound on the size that will be allocated and then you might as well just use a normal array. Darryl Darryl 5, 1 1 gold badge 23 23 silver badges 30 30 bronze badges.
Jens Gustedt Jens Gustedt JeremyP JeremyP It's true that pointers are not booleans, but in C, if-statements don't take booleans: they take integer expressions.
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