Manual Memory Management

Replacements for malloc() and free()

Manual memory management dictates that the engineer writing a program must keep track of the memory allocated. This forces all of the bookkeeping to be performed when the program is being designed instead of while the program is running. This can benefit execution speed because the related bookkeeping instructions are not placed in the application itself. However, if a programmer makes an accounting error, they could be faced with a memory leak or a dangling pointer. Nevertheless, properly implemented manual memory management is lighter and faster than the alternatives.

In ANSI C, manual memory management is provided by the malloc() and free() standard library calls. There are two other standard library functions (calloc() and realloc()), they resolve to calls to malloc() and free().

I thought that the best way to illustrate how manual memory management facilities are constructed would be to offer several different implementations of malloc() and free(). To use these alternative implementations, all you will need to do is include the appropriate source file and then call newMalloc() and newFree() instead of malloc() and free(). For example:

#include

void main()
{
   char *cptr;
   initMemMgr();

   cptr = newMalloc(10);
   if(cptr==NULL){ printf("allocation failed!\n"); }
   newFree(cptr);

   closeMemMgr();
   return;
}

The remainder of this chapter will be devoted to describing three different approaches. In each case, I will present the requisite background theory, offer a concrete implementation, provide a test driver, and look at associated trade-offs. Along the way, I will also discuss performance measuring techniques and issues related to program simulation.