Memory Functions in C

Author: Imon Mallik
GitHub: https://github.com/computerman2027/Memory-Functions-in-C.git

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📌 Overview

This repository demonstrates the working of important memory manipulation functions in C from <string.h>:

• memchr()
• memcmp()
• memcpy()
• memmove()
• memset()

Each function is explained using multiple practical examples, including: - Byte-level memory visualization - Endianness observation (Little Endian systems) - Struct copying - Partial memory copying - Overlapping memory issues - Binary data comparison - Embedded NULL character behavior

The goal of this repository is to deeply understand how memory works at the byte level in C.

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📂 Project Structure

memchrdemo/
memcmpdemo/
memcopydemo/
memsetdemo/

Each folder contains demonstration programs related to one memory function.

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🔍 memchr() Demonstration

📁 memchrdemo/memchrdemo_1.c

Function Used:

void *memchr(const void *ptr, int value, size_t num);

What It Does:

Searches for the first occurrence of a byte in a block of memory.

Demonstration:

• Searches integer array memory byte-by-byte.
• Shows that memchr() works on raw bytes, NOT integers.
• Demonstrates how integer values are stored in memory.

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🔎 memcmp() Demonstrations

📁 memcmpdemo/memcmpdemo_1.c

• Compares two identical integer arrays.
• Prints decimal, hexadecimal, and actual byte-level memory.
• Shows that memcmp() returns 0 for identical memory blocks.

📁 memcmpdemo/memcmpdemo_2.c

• Compares slightly different integer arrays.
• Demonstrates non-zero return value.

📁 memcmpdemo/memcmpdemo_3.c

• Compares int[] with short int[].
• Demonstrates byte-level comparison across different data types.

📁 memcmpdemo/memcmpdemo_4.c

• Demonstrates how integer values may contain embedded short values.
• Shows memory alignment behavior.

📁 memcmpdemo/memcmpdemo_5.c

• Demonstrates endianness impact on comparison.

📁 memcmpdemo/memcmpdemo_6.c

• Compares strcmp() vs memcmp().
• Cases demonstrated:
  • Equal strings
  • Lexicographical difference
  • Different lengths
  • Embedded NULL characters
  • Signed vs unsigned char
  • Binary data comparison

Function Used:

int memcmp(const void *ptr1, const void *ptr2, size_t num);

Key Learning:

memcmp() compares raw memory byte-by-byte, not logical values.

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📦 memcpy() Demonstrations

📁 memcopydemo/memcopydemo_1.c

• Copies entire integer array.
• Shows before and after memory representation.

📁 memcopydemo/memcopydemo_2.c

• Demonstrates partial memory copying.
• Copies only part of an array.

📁 memcopydemo/memcopydemo_3.c

• Copies an entire struct.
• Shows raw memory layout of structure.
• Demonstrates structure padding effects.

📁 memcopydemo/memcopydemo_4.c

• Demonstrates overlapping memory issue.
• Shows undefined behavior with overlapping regions.

📁 memcopydemo/memcopydemo_5.c

• Another overlapping example.
• Highlights why memcpy should not be used when memory overlaps.

Function Used:

void *memcpy(void *dest, const void *src, size_t num);

Key Learning:

• Fast memory copying.
• Undefined behavior when memory regions overlap.

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🔁 memmove() Demonstration

📁 memcopydemo/memmovedemo_4.c

Function Used:

void *memmove(void *dest, const void *src, size_t num);

What It Demonstrates:

• Safe copying when memory regions overlap.
• Correct behavior compared to memcpy.

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🧹 memset() Demonstrations

📁 memsetdemo/memsetdemo_1.c

• Sets integer memory using byte values.
• Shows how memset sets byte-by-byte, NOT integer-by-integer.

📁 memsetdemo/memsetdemo_2.c

• Demonstrates pointer arithmetic effects.
• Shows impact of unaligned memory modification.
• Demonstrates how altering memory at byte level changes integer values.

Function Used:

void *memset(void *ptr, int value, size_t num);

Key Learning:

memset() fills memory byte-by-byte.

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🧠 Core Concepts Covered

• Little Endian memory representation
• Byte-level memory inspection
• Pointer arithmetic
• Structure padding
• Undefined behavior
• Overlapping memory issues
• Signed vs unsigned comparison
• Difference between logical comparison and raw memory comparison

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🛠 How to Compile

Using GCC:

gcc filename.c -o output
./output

Example:

gcc memcmpdemo_1.c -o memcmpdemo_1
./memcmpdemo_1

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🎯 Purpose of This Repository

This project is created for:

• Deep understanding of memory in C
• Interview preparation
• Systems programming fundamentals
• Strengthening pointer and memory concepts

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⭐ Final Note

This repository is meant for educational purposes to help understand how memory manipulation functions operate internally at the byte level.

Happy Coding 🚀