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Do not convert a pointer value to a pointer type that is more strictly aligned than the referenced type the value actually points to. Different alignments are possible for different types of objects. If the type-checking system is overridden by an explicit cast or the pointer is converted to a void pointer (void *) and then to a different type, the alignment of an object may be changed.

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In this compliant solution, the char value is stored into an object of type int so that the pointer's value will be properly aligned:

#include <assert.h>
 
void func(void) {
  char c = 'x';
  int i = c;
  int *ip = (int *)&i;

  assert(ip == &i);
}

Compliant Solution (C11, alignas())

This compliant solution uses the alignment specifier to declare the char object c with the same alignment as that of an object of type int. As a result, the two pointers reference equally aligned pointer types:

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The C Standard allows any object pointer to be cast to and from void *. As a result, it is possible to silently convert from one pointer type to another without the compiler diagnosing the problem by storing or casting a pointer to void * and then storing or casting it to the final type. In this noncompliant code example, loop_function() is passed the char pointer loop_ptr but returns an object of type int pointer:

int *loop_function(void *v_pointer) {
  /* ... */
  return v_pointer;
}
 
void func(char *loop_ptr) {
  int *int_ptr = loop_function(loop_ptr);

  /* ... */
}

This example compiles without warning. However, v_pointer can be more strictly aligned than an object of type int *.

Compliant Solution

Because the input parameter directly influences the return value, and loop_function() returns an object of type int *, the formal parameter v_pointer is redeclared to accept only an object of type int *:

int *loop_function(int *v_pointer) {
  /* ... */
  return v_pointer;
}
 
void func(int *loop_ptr) {
  int *int_ptr = loop_function(loop_ptr);

  /* ... */
}

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Some architectures require that pointers are correctly aligned when accessing objects larger than a byte. However, it is common is in system code that unaligned data (for example, the network stacks) must be copied to a properly aligned memory location, such as in this noncompliant code example:

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EXP36-EX1: Some hardware architectures have relaxed requirements with regard to pointer alignment. Using a pointer that is not properly aligned is correctly handled by the architecture, although there might be a performance penalty. On such an architecture, improper pointer alignment is permitted , but remains an efficiency problem.

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