Using a Constant Character Pointer in a std::set Container: Memory Consumption

Question

I'm currently working on a device with very little memory (4MB) and I have a component of my program that requires an std::set. I would like to migrate this set from using std::string to using const char pointers but I was wondering how memory is allocated to constant character pointers when used in a std::set.

Will the memory allocated for each entry to the std::set be freed when the pointer is removed from the set (by using .clear() or going out of scope), or will the string literal remain in memory until the end of the program's execution?

Thank you very much for your help. :)

It really funny how nowadays we consider 4M to be a small amount of memory. I remember the days when a whole OS would fit in 8K or less (and an application in a fraction of that). — Martin York, Feb 20 '11 at 00:17

score 1 · Answer 1 · answered Feb 19 '11 at 23:55

1

In short, nothing special will happen.

Deleting a structure that contains a pointer to some memory will only free the memory used by the pointer itself; it will not cause anything to happen to the pointed-to memory.

Unless, of course, you explicitly call free/delete on it. Which is not a good idea in the case of string literals!

answered Feb 19 '11 at 23:55

Oliver Charlesworth

267,707
33
569
680

Thank you for the quick response! :) Do you have any suggestions for alternate solutions? Is there a way to create a set of character arrays? – Wheatevo Feb 19 '11 at 23:58

score 0 · Accepted Answer · answered Feb 19 '11 at 23:58

The STL containers always calk the default destructors for elements they contain when they are cleaned up. For a set holding raw ‘char *‘ pointers, this will do nothing and the memory will be leaked. You are responsible for cleaning ip this sort of memory yourself.

For this reason, it's generally considered bad practice to store raw pointers in STL containers.

If you really must use an STL set with raw C strings in it, that's fine, but do be aware that you'll have to reclaim the memory yourself. You will also need to provide a custom comparator to the set so that e stored strings are compared by value rather than by pointer (the default ordering on ‘char *‘s just compares the pointers, not the strings).

If the OP really means "string literals", then no memory cleanup is required. — Oliver Charlesworth, Feb 19 '11 at 23:59
@Oli Charlesworth- Agreed, but since this wasn't mentioned explicitly I'm not going to assume it. But you're right - if it's just string literals, no cleanup is necessary. — templatetypedef, Feb 20 '11 at 00:12

Using a Constant Character Pointer in a std::set Container: Memory Consumption

2 Answers2