9.6 Dynamic Memory Allocation

The run-time heap is an uninitialized area of data memory that is used for dynamic memory allocation using the standard C library dynamic memory management functions, calloc, malloc and realloc along with the C++ new operator. Most C++ applications will require a heap.

If you do not use any of these functions, then you do not need to allocate a heap. By default, a heap is not created.

In MPLAB X, you can specify a heap size in the project properties for the xc32-ld linker. MPLAB X will automatically pass the option to the linker when building your project.

If you do want to use dynamic memory allocation, either directly, by calling one of the memory allocation functions, or indirectly, by using a standard C library function that uses one of these functions, then a heap must be created. A heap is created by specifying its size on the linker command line using the --defsym=_min_heap_size linker command line option. An example of allocating a heap of 512 bytes using the command line is:

xc32-gcc foo.c -Wl,--defsym=_min_heap_size=512

An example of allocating a heap of 0xF000 bytes using the xc32-g++ driver is:

xc32-g++ vector.cpp -Wl,--defsym=_min_heap_size=0xF000

The linker allocates the heap immediately before the stack.