The __heapstats() functiondisplays statistics on the state of the storage allocation heap. It calls the __Heap_Stats() function, which you can re-implement if you choose to do your own storage management (see __Heap_Stats()). The ARM default implementation gives information on how many free blocks exist, and estimates their size ranges.

Example 4.20 shows an example of the output from __heapstats(). Line 1 of the output displays the total number of bytes, the number of free blocks, and the average size. The following lines give an estimate the size of each block in bytes, expressed as a range. __heapstats() does not give information on the number of used blocks.

The function outputs its results by calling the output function dprint, which must work like fprintf(). The first parameter passed to dprint is the supplied pointer param. You can pass fprintf() itself, provided you cast it to the right function pointer type. This type is defined as a typedef for convenience. It is called __heapprt. For example:

If you are using the default single-region memory model, heap memory is allocated only as it is required. This means that the amount of free heap changes as you allocate and deallocate memory. For example, as sequence such as:

  int *ip;
  __heapstats((__heapprt)fprintf,stderr);   // print initial free heap size
  ip = malloc(200000);
  free(ip);
  __heapstats((__heapprt)fprintf,stderr);    // print heap size after freeing

gives output such as:

This function is an ARM-specific library extension.