What are the contents of the memory just allocated by `malloc()`?

Question

I was curious about what exactly a pointer holds, after malloc() was used to allocate memory space? The manpage tells me that calloc() initializes

Answer 1

It's undefined by the C language what the memory block contains when you get it. In practice it will most likely simply contain what was in that physical memory previously.

If the memory was previously used by your program and freed you'll likely just get what was in it before. If it's memory newly requested from the operating system you'll get what the operating system put in it. Most operating systems return memory that has been specifically set to 'zero' bytes because it would be a security issue if the memory still contained what was in it from some other program previously.

None of that is guaranteed by any standard, it's just what most systems do in practice.