Any gcc options to allow ((int *)p)++

Question

Some C compilers can sometimes deduce a casted pointer as still a lvalue, but gcc defaults won't compile it. Instead of having to port (by human-error-prone way)legacy code base to:

p=(int *)p+1 ; /* increment by sizeof(int) */

can gcc be made to allow this code below (even if not technically correct)?

void f() {
    void *p ; /* type to be cast later for size */
    ((int *)p)++ ; /* gcc -c f.c => lvalue required error */ }

Edit: even if technically incorrect, I assume the only programmer intent for such code is for p to remain lvalue and "increment" it, generating same code as my long form, right? (perreal flagged as "lvalue cast")

Edit2: We all agree refactoring to std C is best, but if something like Mateo's -fpermissive worked, it might not catch future programming errors, but hoping initial gcc porting effort will be less faulty... Any other similar suggestions?

This used to be supported by GCC (https://stackoverflow.com/questions/21386485/why-isnt-the-result-of-this-cast-an-lvalue) but not anymore. — AnT stands with Russia, May 20 '18 at 02:29

score 1 · Answer 1 · answered May 19 '18 at 12:58

If you want to clean up your code(remove excessive casts) , you can concentrate the ugly casts inside a macro or, even better, an inlined function. The below fragment only makes use of implicit casts to/from void*

You are ,of course, still responsible for the proper alignment.

#include <stdio.h>

static void *increment(void * p,size_t offset)
{
char *tmp = p;
return tmp+offset;
}

int main(void)
{
void *ptr = "Hell0 world!\n";

ptr = increment( ptr, sizeof(int) );

printf("%s", (char*) ptr);

return 0;
}

Any gcc options to allow ((int *)p)++

1 Answers1