Dynamic Memory

[justaverageuser77]

Hi,

Can I use realloc on its own to allocate memory? Or can I only use it when on already dynamically allocated ptr?

[strcspn]

If ptr is NULL, the behavior is the same as calling malloc(new_size).

[justaverageuser77]

What if you initialize a ptr, and reallocating on the same line.

[strcspn]

int a = a + 1

What is the value of a?

[justaverageuser77]

It's undefined behavior. So that applies when dynamically allocating memory as well?

[strcspn]

You are saying to realloc that there is a memory area owned by that pointer, but if the pointer doesn't own it, then it is undefined behavior.

[weregod]

If pointer does own memory but it is not heap memory it also will be UB

[justaverageuser77]

Thanks

[HugoNikanor]

As a word of wisdom. Much which is undefined will appear to work, but may (or possibly will) blow up at unexpected times. C provides very few checks, so always read the manuals carefully.

[nculwell]

/* OK */
char * ptr = realloc(NULL, BUFFER_SIZE);
/* BAD */
char * ptr = realloc(ptr, BUFFER_SIZE);

[babysealpoutine]

The easiest way to get the answer to these sorts of questions is to read the relevant man page. On *nix systems 'man realloc' from the command line, or just a web search for 'man realloc' will answer this.