Understanding Memory Allocation, Heap Layout, and Fragmentation in C

The author introduces memory allocation by asking what happens inside the computer when a block of memory is requested, using a simple C example and showing a code snippet that calls malloc .

He explains that malloc belongs to the standard library, which also contains mathematical functions, character handling functions, string manipulation functions, and other memory‑management functions like free .

The article distinguishes between the programmer's source files (e.g., .c files) and the compiled output, describing how the compiler turns source code into object files, and how the linker combines object files with the standard library to produce an executable.

It then describes the memory layout of a running program, highlighting the code segment, data segment, stack segment, and heap segment, and emphasizes that dynamic allocations performed by malloc reside in the heap.

Using a locker analogy, the author illustrates that memory is divided into equal‑sized slots (bytes) with addresses, and that a pointer is simply the address of a slot.

The process of allocating the first block (A) in an empty heap is shown, followed by subsequent allocations (B, C) placed sequentially after the previous blocks.

When a block (A) is freed, its region becomes a free chunk, creating potential fragmentation; the article defines memory fragmentation as free space that cannot satisfy a larger allocation request.

It discusses a scenario where a request for a larger block (D) cannot be satisfied by any single free chunk even though the total free space is sufficient, illustrating internal fragmentation.

To resolve this, the author explains that the operating system can be asked (e.g., via the brk system call on Linux) to extend the heap, after which a suitable free region can be found and the allocation completes.