C Interfaces and Implementations: Techniques for Creating Reusable Software

Chapter 5. Memory Management

All nontrivial C programs allocate memory at runtime. The standard C library provides four memory-management routines: malloc, calloc, realloc, and free. The Mem interface repackages these routines as a set of macros and routines that are less prone to error and that provide a few additional capabilities.

Unfortunately, memory-management bugs are common in C programs, and they are often difficult to diagnose and fix. For example, the fragment

   p = malloc(nbytes);
   ...
   free(p);

calls malloc to allocate a block of nbytes of memory, assigns the address of the first byte of that block to p, uses p and the block it points to, and frees the block. After the call to free, p holds a dangling pointer — a pointer that refers to ...