Why does a C-Array have a wrong sizeof() value when it’s passed to a function? [duplicate]

by

When you pass an array into a function in C, the array decays into a pointer to its first element. When you use sizeof on the parameter, you are taking the size of the pointer, not the array itself.

If you need the function to know the size of the array, you should pass it as a separate parameter:

void test(int arr[], size_t elems) {
   /* ... */
}

int main(int argc, const char * argv[]) {
   int point[3] = {50, 30, 12};
   /* ... */
   test(point, sizeof(point)/sizeof(point[0]));
   /* ... */
}

Also note that, for a similar reason (taking the sizeof a pointer), the sizeof(point)/sizeof(point[0]) trick doesn’t work for a dynamically allocated array, only an array allocated on the stack.

More Related Contents:

  1. Why isn’t the size of an array parameter the same as within main?
  2. C sizeof a passed array [duplicate]
  3. How to find the ‘sizeof’ (a pointer pointing to an array)?
  4. Passing an array as an argument to a function in C
  5. Difference between passing array and array pointer into function in C
  6. Allocate memory 2d array in function C
  7. Pass an array to a function by value
  8. What does ‘sizeof (function name)’ return?
  9. Returning Arrays/Pointers from a function
  10. How can I find the number of elements in an array?
  11. Why use an asterisk “[*]” instead of an integer for a VLA array parameter of a function?
  12. Changing array inside function in C
  13. How to get the string size in bytes?
  14. Getting the size of a malloc only with the returned pointer
  15. C – SizeOf Pointers
  16. C pointers and arrays/ ‘sizeof’ operator [duplicate]
  17. How to find the size of an array (from a pointer pointing to the first element array)?
  18. When is an array name or a function name ‘converted’ into a pointer ? (in C)
  19. How can I return a character array from a function in C?
  20. Manipulate multidimensional array in a function
  21. Access struct members as if they are a single array?
  22. Passing an Array by reference in C
  23. Reliably determine the number of elements in an array
  24. Find size of array without using sizeof
  25. How can I malloc a struct array inside a function? Code works otherwise
  26. Why is the size of a function in C always 1 byte?
  27. C pointer notation compared to array notation: When passing to function
  28. I need help understanding this code in C [closed]
  29. Implementation of sizeof operator
  30. Function declaration inside of function — why?

Leave a Comment