Memory management is a fundamental concept in C programming. Programs use different types of memory for different purposes. The stack stores local variables and function call information, while the heap is used for dynamic memory allocation. Understanding these memory regions is essential for effective C programming and proper use of malloc and free functions.
The malloc function is the primary way to allocate memory dynamically in C. It takes one parameter - the number of bytes to allocate - and returns a void pointer to the allocated memory block. The function is declared in stdlib.h header file. When malloc is called, it searches the heap for a free block of sufficient size and returns a pointer to it. If no suitable block is found, malloc returns NULL to indicate failure.
Now let's see malloc in action with practical examples. For a single integer, we use malloc with sizeof int to allocate 4 bytes. For an array of 10 integers, we multiply 10 by sizeof int to get 40 bytes. For structures, we use sizeof with the structure name. Each malloc call returns a pointer that we must cast to the appropriate type. The memory diagram shows how different allocations occupy different amounts of heap space.
The free function is essential for proper memory management in C. It takes a pointer as parameter and deallocates the memory block that was previously allocated by malloc. The function signature is simple - void free with a void pointer parameter. After calling free, the memory becomes available for future allocations. It's crucial to follow proper rules: every malloc must have a matching free, set the pointer to NULL after freeing, never use freed memory, and never free the same pointer twice. This prevents memory leaks and program crashes.
Memory management errors are common sources of bugs in C programs. Memory leaks occur when allocated memory is never freed, causing the program to consume more and more memory over time. Double free errors happen when you call free on the same pointer twice, which can crash the program. Dangling pointers occur when you try to use memory after it has been freed. To prevent these errors, always check malloc return values, set pointers to NULL after freeing them, and use debugging tools like valgrind to detect memory issues during development.