C Language Memory Management: Key Concepts and Examples

Introduction

Memory management in C is critical for efficient and bug-free programs. C requires manual memory handling, which offers control but demands care to avoid leaks and crashes. This guide focuses on practical code examples to demonstrate memory management techniques.

Memory Segments in C

• Stack: Local variables, auto-managed.
• Heap: Dynamic memory, manually managed.
• Static/Global: Persistent variables.
• Code/Text: Program instructions.

Dynamic Memory Allocation Examples

1. Using malloc()

Allocate memory for an array of 5 integers.

#include <stdlib.h>
#include <stdio.h>

int main() {
    int *arr = (int *)malloc(5 * sizeof(int));
    if (arr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    for (int i = 0; i < 5; i++) {
        arr[i] = i + 1;
        printf("%d ", arr[i]);
    }
    free(arr);
    arr = NULL;
    return 0;
}

2. Using calloc()

Allocate and initialize memory to zero for 3 doubles.

#include <stdlib.h>
#include <stdio.h>

int main() {
    double *values = (double *)calloc(3, sizeof(double));
    if (values == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    for (int i = 0; i < 3; i++) {
        printf("%.1f ", values[i]); // Prints 0.0
    }
    free(values);
    values = NULL;
    return 0;
}

3. Using realloc()

Resize an existing array to hold 10 integers.

#include <stdlib.h>
#include <stdio.h>

int main() {
    int *arr = (int *)malloc(5 * sizeof(int));
    if (arr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    for (int i = 0; i < 5; i++) {
        arr[i] = i + 1;
    }
    arr = (int *)realloc(arr, 10 * sizeof(int));
    if (arr == NULL) {
        printf("Reallocation failed!\n");
        return 1;
    }
    for (int i = 5; i < 10; i++) {
        arr[i] = i + 1;
    }
    for (int i = 0; i < 10; i++) {
        printf("%d ", arr[i]);
    }
    free(arr);
    arr = NULL;
    return 0;
}

Handling Common Issues

Avoiding Memory Leaks

Always free allocated memory.

#include <stdlib.h>
#include <stdio.h>

int main() {
    int *ptr = (int *)malloc(sizeof(int));
    if (ptr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    *ptr = 42;
    printf("Value: %d\n", *ptr);
    free(ptr); // Prevents memory leak
    ptr = NULL; // Avoids dangling pointer
    return 0;
}

Preventing Dangling Pointers

Set pointers to NULL after freeing.

#include <stdlib.h>
#include <stdio.h>

int main() {
    char *str = (char *)malloc(10 * sizeof(char));
    if (str == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    strcpy(str, "Hello");
    printf("%s\n", str);
    free(str);
    str = NULL; // Prevents accidental use
    if (str == NULL) {
        printf("Pointer is NULL, safe!\n");
    }
    return 0;
}

Avoiding Segmentation Faults

Check for valid memory access.

#include <stdlib.h>
#include <stdio.h>

int main() {
    int *arr = (int *)malloc(3 * sizeof(int));
    if (arr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    for (int i = 0; i < 3; i++) {
        arr[i] = i;
        printf("%d ", arr[i]);
    }
    // Avoid accessing arr[3] to prevent segfault
    free(arr);
    arr = NULL;
    return 0;
}

Best Practices with Code

Modular Memory Management

Encapsulate allocation/deallocation in functions.

#include <stdlib.h>
#include <stdio.h>

int *create_array(int size) {
    int *arr = (int *)malloc(size * sizeof(int));
    if (arr == NULL) {
        return NULL;
    }
    for (int i = 0; i < size; i++) {
        arr[i] = i;
    }
    return arr;
}

void free_array(int *arr) {
    if (arr != NULL) {
        free(arr);
    }
}

int main() {
    int *arr = create_array(5);
    if (arr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    for (int i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }
    free_array(arr);
    return 0;
}

Memory Pool Example

Simple memory pool for fixed-size blocks.

#include <stdlib.h>
#include <stdio.h>

#define BLOCK_SIZE 32
#define POOL_SIZE 10

typedef struct {
    char pool[POOL_SIZE][BLOCK_SIZE];
    int used[POOL_SIZE];
} MemoryPool;

void init_pool(MemoryPool *pool) {
    for (int i = 0; i < POOL_SIZE; i++) {
        pool->used[i] = 0;
    }
}

char *alloc_block(MemoryPool *pool) {
    for (int i = 0; i < POOL_SIZE; i++) {
        if (!pool->used[i]) {
            pool->used[i] = 1;
            return pool->pool[i];
        }
    }
    return NULL;
}

void free_block(MemoryPool *pool, char *block) {
    for (int i = 0; i < POOL_SIZE; i++) {
        if (pool->pool[i] == block) {
            pool->used[i] = 0;
            break;
        }
    }
}

int main() {
    MemoryPool pool;
    init_pool(&pool);
    char *block1 = alloc_block(&pool);
    if (block1) {
        strcpy(block1, "Test");
        printf("%s\n", block1);
    }
    free_block(&pool, block1);
    return 0;
}

Debugging Tools

• Valgrind: Run valgrind --leak-check=full ./program to detect leaks.
• AddressSanitizer: Compile with -fsanitize=address for runtime checks.
• GDB: Use gdb ./program to debug segfaults.

Conclusion

Effective memory management in C requires careful use of allocation functions, error checking, and cleanup. The examples above demonstrate practical techniques to allocate, manage, and free memory while avoiding common issues like leaks and segfaults. Practice these patterns to write robust C programs.