Pointers in C: when to use the ampersand and the asterisk?

by

You have pointers and values:

int* p; // variable p is pointer to integer type
int i; // integer value

You turn a pointer into a value with *:

int i2 = *p; // integer i2 is assigned with integer value that pointer p is pointing to

You turn a value into a pointer with &:

int* p2 = &i; // pointer p2 will point to the address of integer i

Edit:
In the case of arrays, they are treated very much like pointers. If you think of them as pointers, you’ll be using * to get at the values inside of them as explained above, but there is also another, more common way using the [] operator:

int a[2];  // array of integers
int i = *a; // the value of the first element of a
int i2 = a[0]; // another way to get the first element

To get the second element:

int a[2]; // array
int i = *(a + 1); // the value of the second element
int i2 = a[1]; // the value of the second element

So the [] indexing operator is a special form of the * operator, and it works like this:

a[i] == *(a + i);  // these two statements are the same thing

More Related Contents:

  1. Pointers program
  2. Are there differences between pointers to object stored on stack and heap? [closed]
  3. With arrays, why is it the case that a[5] == 5[a]?
  4. Length of array in function argument
  5. What is the difference between char * const and const char *?
  6. In C, are arrays pointers or used as pointers?
  7. Are all data pointers the same size in one platform for all data types? [duplicate]
  8. How do I understand complicated function declarations?
  9. How can I allocate memory and return it (via a pointer-parameter) to the calling function?
  10. Pointer Arithmetic In C
  11. C pointers : pointing to an array of fixed size
  12. Array to pointer decay and passing multidimensional arrays to functions
  13. Why does this code segfault on 64-bit architecture but work fine on 32-bit?
  14. C: Which character should be used for ptrdiff_t in printf?
  15. Why doesn’t scanf need an ampersand for strings and also works fine in printf (in C)?
  16. How to print variable addresses in C?
  17. Returning Arrays/Pointers from a function
  18. why is array name a pointer to the first element of the array?
  19. C – Accessing data AFTER memory has been free()ed?
  20. allocate matrix in C
  21. Passing two-dimensional array via pointer
  22. Getting the size of a malloc only with the returned pointer
  23. Mis-aligned pointers on x86
  24. How to find the size of an array (from a pointer pointing to the first element array)?
  25. Can I treat a struct like an array?
  26. When is it valid to access a pointer to a “dead” object?
  27. How to check if a pointer is freed already in C?
  28. Returning a struct pointer
  29. Casting void pointers
  30. Cast T[][] to T*

Leave a Comment