Tricks to analyse pointer and pointer-to-pointer structures in C?

by

My favorite trick for situations in which I lose track of pointers, is using pen and paper.
Draw rectangles for variables and arrows for pointers.
Draw the arrow from the variable-rectangle which is the pointer variable to the rectangle it points to.

It does not work quite as intuitively in ASCII art as on paper, but it looks somewhat like this.

data [ 0 ][ 1 ][ 2 ][ 3 ][ 4 ]
       ^    ^    ^    ^   ^^
       |    |    |    |.../|     ("..." meaning chronologically progressing,
       |    |    |    "https://stackoverflow.com/"            though this one is the fourth step)
       |    |    |    "https://stackoverflow.com/"
p    [ | ][ | ][ | ][ |/][ | ]

       ^    ^    ^    ^ 
       |... |... |... |             (here are the first three steps)
      ptr

Note that ptr never points to index 4 in p, but instead the pointer in index 3 is incremented, so that it points to index 4 of data. (Admittedly I did not really go to that detail, I focus my question on the trick, not the result of doing it on your code. I might have misread the intentionally hard to read operator uses…)

More Related Contents:

  1. What is pointer to string in C?
  2. What is the output of the following code in C? [closed]
  3. Incorrect result in c code
  4. whats the difference between dynamic memory allocation and normal memory allocation?
  5. pointer to string concept in c [closed]
  6. Pointer manipulation inside function
  7. Changing address contained by pointer using function
  8. Why is the asterisk before the variable name, rather than after the type?
  9. What’s the difference between a VLA and dynamic memory allocation via malloc?
  10. Why does this implementation of offsetof() work?
  11. Why can’t I cast a function pointer to (void *)?
  12. Constant pointer vs Pointer to constant [duplicate]
  13. Can the size of pointers vary between data and function pointers?
  14. Addresses of two char pointers to different string literals are same
  15. Difference between char* and const char*?
  16. In C, what is the correct syntax for declaring pointers?
  17. C typedef of pointer to structure
  18. Pointers – Difference between Array and Pointer
  19. Are “malloc(sizeof(struct a *))” and “malloc(sizeof(struct a))” the same?
  20. C – SizeOf Pointers
  21. Swapping pointers in C (char, int)
  22. What is double star (eg. NSError **)?
  23. Where in memory are string literals ? stack / heap? [duplicate]
  24. How to include a dynamic array INSIDE a struct in C?
  25. How can I return a character array from a function in C?
  26. C difference between *[] and **
  27. Difference between *ptr[10] and (*ptr)[10]
  28. How are we able to access the pointer after deallocating the memory?
  29. In C, is it good form to use typedef for a pointer?
  30. What is the function of an asterisk before a function name?

Leave a Comment