NULL Pointer | C Programming Tutorial

An explanation of the NULL pointer value in C, including common use cases of the NULL pointer value. Source code: github.com/portfoliocourses/c.... Check out www.portfoliocourses.com to build a portfolio that will impress employers!

[@grimvian]

Thanks for clearing the understanding of NULL pointers. I learned a lot, despite I have worked with pointers for some time. I am wondering about your use the command line is for educational purposes... I was positively surprised that you also covered a bit of using struct/nodes. A suggestion for pedagogical reasons at least for me and maybe others: If the struct and the related code can be seen, without scrolling, will make your explanation easier to understand. English is my second language, but I dare to suggest to rephrase the title to: "The versatile use of NULL pointers".

[@PortfolioCourses]

Thanks for the suggestions. :-) I put the struct up at the top of the file to keep it global as is more normal. I try to keep the titles shorter because I've found the video performs better that way, and I try to put more details into the description (like in this case I referenced use cases in the description).

[@grimvian]

@@PortfolioCourses Thanks - I have only heard one other instructor who pronouce char as car - no issue :o)
This is of course an educational situation. Is the tendency to have functions not bigger than a screen size and not wider 80 characters to have the code as clear and understandable as possible or?

[@heitorheitorheitor8158]

man I love your videos they helped me so much 😊

[@PortfolioCourses]

That's awesome that these videos are helping you! :-)

[@ramakrishna4092]

Thanks

[@PortfolioCourses]

Thank you Rama! :-)

[@idanmariani8601]

love everything about your channel i also buy your linked list course super awsome.. :)

[@PortfolioCourses]

Thank you for the kind feedback Idan, and I hope you enjoyed the course! :-)

[@badrinarayanan]

Thank you very much for these videos!

[@PortfolioCourses]

WOW - thank you very much!!!!!! :-D

[@pwnwriter]

Awesome vid as always

[@PortfolioCourses]

I'm really glad to hear you think they're awesome, thank you! :-)

[@ramakrishna4092]

Hi sir I have a doubt here when you free the pointer the memory before and after is same I noticed can you pls tell me why .... I have seen this video two times but I have problem with my understanding. Can you pls help me with that .

[@PortfolioCourses]

It's the same before and after calling free() because free() doesn't modify the memory address that the pointer stores. The function just doesn't do that. All free() does is "make the block of memory that was free'd available again". So when we use malloc() to allocate memory, there is some block of memory that is set aside to be used for our program. Calling free() will make this memory available again, it will no longer be set aside for our program. When we call malloc it returns the memory address for the block of memory that is allocated and we store that into a pointer variable. But free() does not actually modify the value that the pointer variable stores, it ONLY frees the memory AT that memory address. So that's why after calling free() the pointer is the same. And that's why it's a best practice to set a pointer variable to NULL after calling free if we intend to re-use that pointer variable again later, because we are making it clear to the rest of our program that the pointer "points to nothing" which helps prevent us from accidentally using it as if it were pointing to valid memory. :-)

[@vicsteiner]

Thanks again! Another very clear video. In my case (Ubunto + gcc) the realloc was returning a new address in both cases passing the malloc array or the NULL pointer. Not sure why. My doubt is, when realloc returns a new pointer do the old one gets freed automatically?

[@grimvian]

In the video at 6:00, I'm wondering:
if (ptr != NULL) {
*ptr = 5;
printf("*ptr: %d
", *ptr);
// should free only be used here, because malloc only allocate , when ptr != NULL or?
}

[@PortfolioCourses]

You could do it that way, this video is just for demonstration and learning purposes. In general if we can't allocate memory correctly we would probably do something more than just output an error message, we might exit the program for example. In this video we're just exploring the NULL pointer value. 🙂

[@Mnogojazyk]

Can one make a substitute for free() so that it would free the pointer and then nullify the pointer? I have in mind something like
void lose(void ptr)
{
free(ptr) ;
ptr = NULL ;
}

[@PortfolioCourses]

That's a great question and yes I think you could do that, but you would want to pass the pointer "by reference" aka "pass by pointer" in order to set the pointer to point to NULL. So something like this maybe...
void my_free(int **pointer)
{
free(*pointer);
*pointer = NULL;
}
....
int *mypointer = malloc(sizeof(int));
free(&mypointer);
I'm sure it could be made more general with void but maybe I can make a video on this one day.

[@Mnogojazyk]

@@PortfolioCourses, I think a generalised procedure and a video would be great.
Thanks!

[@PortfolioCourses]

@@Mnogojazyk Cool! 🙂

[@KasualNoBrainer]

i have to say it... bro is better than bro code

[@PortfolioCourses]

Thank you for the kind feedback. :-)

[@poisonmods]

Hummmm

[@PortfolioCourses]

I hope you enjoyed it! :-)

[@mohokhachai]

Out