CODEWITHSUNDEEP
c++arrayspointerslinked-list
Nawar
Nawar

Reputation: 1

Store and retrieve address/pointer to char array

Let's say we have a char array:

char pool[1000];

and a pointer

char* ptr;

the pointer stores an address to a block of data in Pool. I want to store this address in the pool and retrieve it as well.

Basically, what I want to do is a linked-list that is embedded in the char array Pool. The reason is that i'm not allowed to create any new variables (globally), and I cant include new headers, among other restrictions.

So the question is : how to I segment and fit a 4 byte address in (let's say) the first 4 elements of pool[] , and how do I retrieve it again for the purpose of modification.

This operation will happen frequently so it needs to be fast...and of course not rely of external functions.

Upvotes: 0

Views: 3119

Answers (2)

dmitri
dmitri

Reputation: 3294

If you want to store ptr in pool then should you have a pool of addresses instead?

char *pool[1000];

Then

pool[0] = ptr;
ptr = pool[0];
etc.

If you have to deal with a buffer of characters, that is

char pool[1000];

but treat it as a buffer of addresses then bend it by creating a local variable:

char **pp = reinterpret_cast<char**>(&pool);
*pp = ptr;

The later stores ptr at the start of the buffer pool. To retrieve it:

ptr = *pp;

You may move along the pool by incrementing the pointer pp

pp++ // next address

And don't make an assumption that address is 4 bytes!

Upvotes: 0

R Sahu
R Sahu

Reputation: 206607

To store the value of ptr in pool, use:

memcpy(pool, &ptr, sizeof(ptr));

To retrieve the value of the pointer from pool, use:

memcpy(&ptr, pool, sizeof(ptr));

Re:

This operation will happen frequently so it needs to be fast...and of course not rely of external functions.

memcpy is exactly what you need. If you cannot use memcpy, you'll need to implement the exact functionality in your code.

Unless you are able to verify that the calls to memcpy is a performance bottleneck, I would advise using it.

Upvotes: 1

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