CS50 2024 | Memória (Aula 4) - Curso de Introdução à Ciência da Computação de Harvard

Introduction

This tutorial is designed to provide a clear understanding of fundamental concepts in computer science, particularly focusing on memory management, pointers, and file I/O as discussed in CS50's lesson on memory. These concepts are essential for anyone looking to deepen their knowledge in programming and computer science.

Step 1: Understanding Pointers

• Pointers are variables that store the memory address of another variable.
• To declare a pointer in C, use the asterisk (*) symbol. For example:

  int *p;
  

• To assign a value to a pointer, use the address-of operator (&):

  int x = 10;
  p = &x;
  

• Access the value stored at the pointer's address using the dereference operator (*):

  printf("%d\n", *p); // Outputs 10
  

Step 2: Recognizing Segmentation Faults

• A segmentation fault occurs when a program tries to access an area of memory that it shouldn't.
• Common causes include:
  • Dereferencing null pointers.
  • Accessing memory that has been freed.
• Always initialize pointers and check for null before dereferencing.

Step 3: Dynamic Memory Allocation

• Dynamic memory allocation allows you to request memory at runtime using functions like malloc, calloc, and free.
• Use malloc to allocate memory:

  int *arr = malloc(10 * sizeof(int)); // Allocates memory for 10 integers
  

• Always free memory once you're done to prevent memory leaks:

  free(arr);
  

Step 4: Understanding Stack and Heap

• The stack is a region of memory that stores local variables and function call information, managed automatically.
• The heap is used for dynamic memory allocation, where you manage memory manually.
• Stack memory is faster but limited in size, while heap memory is larger but slower.

Step 5: Avoiding Buffer Overflows

• Buffer overflow occurs when data exceeds the boundaries of allocated memory.
• To prevent buffer overflow:
  • Always check the size of input data before processing.
  • Use functions like strncpy instead of strcpy.

Step 6: File Input/Output

• C provides functions for reading from and writing to files, such as fopen, fread, fwrite, and fclose.
• Example of writing to a file:

  FILE *file = fopen("output.txt", "w");
  fprintf(file, "Hello, World!");
  fclose(file);
  

• Always check if a file was opened successfully before performing operations.

Step 7: Working with Images

• Images are composed of pixels, which are the smallest units of a picture.
• Each pixel is represented by binary data (zeros and ones).
• Understanding how to manipulate this data is essential for image processing.

Conclusion

This tutorial covered essential concepts in memory management, including pointers, segmentation faults, dynamic memory allocation, stack vs. heap, buffer overflows, and file I/O. Mastering these concepts is crucial for effective programming and developing robust applications. As a next step, consider practicing these concepts by writing simple programs that incorporate dynamic memory management and file operations.