Not casting pointers in C can cause problems? -


yesterday in class, , @ point instructor talking c code. said:

what purpose of making pointer cast in c? purpose make compiler interpret correctly pointer operations (for example, adding int pointer result in different offset adding char pointer). apart that, there no difference: pointers represented same way in memory, regardless if pointer pointing int value, char value, short value, or whatever. so, casting pointer not modify in memory, programmer operations more related pointer-type dealing with.

however, have read, specially here in stack overflow, not 100% true. have read in weird machines, pointers different types can stored in different ways in memory. in case, not changing pointer correct type cause problems if code compiled kind of machine.

basically, kind of code i'm talking about. consider code below:

int* int_pointer; char* char_pointer; int_pointer = malloc(sizeof(int)); *int_pointer = 4;

and 2 options:

1.

char_pointer = (char *)int_pointer;

2.

char_pointer = int_pointer;

the code on case 2 became problem? making cast (case 1) change pointer format in memory (if yes, give example of machine?)?

thanks

what instructor said pointer types sharing same representation true real-life implementations of c language.

however, not true point of view of abstract c language itself. c language guarantees

  1. char * pointers represented in same way void * pointers.
  2. pointers qualified version of type t (const, volatile, restrict) represented in same way pointers unqualified t.
  3. pointers struct types represented identically.
  4. pointers union types represented identically.

that all. no other guarantees exist. means far language concerned, int * pointer has different representation double * pointer. , pointer struct s represented differently pointer union u.

however, example char_pointer , int_pointer, presented, not illustrative. char_pointer = int_pointer; assignment invalid (as in "does not compile"). language not support implicit conversions between incompatible pointer types. such conversions require explicit cast operator.


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