Array length changeable during Run - Time

You will probably be better off allocating maximum array size at compile time. Dynamic memory allocation in a 8051-based design is generally a bad idea. Just do a search in this forum with keywords like "malloc" or "dynamic" for further discussion.

- mike

"You will probably be better off allocating maximum array size at compile time."

Yes.

Think about it: even if you do use malloc (or similar) you will have to define the size of the "pool" from which this allocates its memory - so you will need to know the maximum array size at compile time anyway.

So why waste your time, and the compiler's, and some CPU run time with dynamic allocation?

Just Don't Do It!

"Is there somthing like malloc()?"

To answer your question directly there is indeed something like malloc(): malloc(), in fact.

However, as others have pointed out using malloc() is a bad idea in most 8051 situations. If you need dynamic allocation because your total memory requirements exceed your available memory then declare arrays as local variables within functions and let the overlay manager perform its magic.

The small model benchmarks for malloc and free may be found at: http://www.keil.com/benchmks/c51_alloc.asp.

The benchmark results are from the Knuth memory allocation test as described in Fundamental Algorithms, Section 2.5 Dynamic Storage Allocation. In other words, the results in the benchmark are likely to be close to what you see in your implementation.

Note that the free() function in the Keil libraries merges adjacent free blocks. This is NOT true of most malloc/free implementations.

Jon

"To answer your question directly there is indeed something like malloc(): malloc(), in fact."

And then to answer your question even more directly about runtime changes, after malloc(), you would use realloc() to change size.

http://www.keil.com/support/man/docs/c51/c51_realloc.htm