Determine size of dynamically allocated memory in C

Question

Is there a way in C to find out the size of dynamically allocated memory?

For example, after

char* p = malloc (100);

Is there

Answer 1

The C mentality is to provide the programmer with tools to help him with his job, not to provide abstractions which change the nature of his job. C also tries to avoid making things easier/safer if this happens at the expense of the performance limit.

Certain things you might like to do with a region of memory only require the location of the start of the region. Such things include working with null-terminated strings, manipulating the first n bytes of the region (if the region is known to be at least this large), and so forth.

Basically, keeping track of the length of a region is extra work, and if C did it automatically, it would sometimes be doing it unnecessarily.

Many library functions (for instance fread()) require a pointer to the start of a region, and also the size of this region. If you need the size of a region, you must keep track of it.

Yes, malloc() implementations usually keep track of a region's size, but they may do this indirectly, or round it up to some value, or not keep it at all. Even if they support it, finding the size this way might be slow compared with keeping track of it yourself.

If you need a data structure that knows how big each region is, C can do that for you. Just use a struct that keeps track of how large the region is as well as a pointer to the region.