Suppose I have the following struct and functions. struct my_struct{int a; char private[10];} void * get_struct_field_nonconst(struct my_struct *ptr) { r

Suppose I have the following struct and functions. struct my_struct{int a; char private[10];} void * get_struct_field_nonconst(struct my_struct *ptr) { return &(ptr->private[0]); } With these elements you are only allowed to give non-const pointers to read or write inside private field. In order to truly apply this to const pointers (no casting etc.) you will need another get_struct_field() function but defined as this. const void * get_struct_field_const(const struct my_struct *ptr) { return &(ptr->private[0]); } This will work but it is ugly. Here _Generic keyword allows you to write these functions but use them with a common name. Such as get_struct_field(). And that would be something like this: #define get_struct_field(ptr) \ _Generic((ptr), \ const struct my_struct * : get_struct_field_const, \ struct my_struct * : get_struct_field_nonconst) \ (ptr) Hope this would help!