When a ptr is passed to a function, how to ensure its address is not changed? See the following cope snippet. Is it possible to make this function inline and achieve the goal?

void test(int *p) {
    printf("%p\n", (void*)&p);
}

int main(void) {
  int a = 10;
  int *p = &a;
  printf("%p\n", (void*)&p);
  test(p);
  return 0;
}

Output is

0x7ffe53b10938
0x7ffe53b10940

Edit: the goal is that I want to maintain the same address in main and test when manipulating the variable p.

CodePudding user response：

It will be easier to understand if you add more prints.

void test(unsigned *pFunc) {
    printf("Address of pFunc %p\n", (void*)&pFunc);
    printf("Address held by pFunc %p\n", (void*)pFunc);
    printf("Object referenced by pFunc: 0x%x\n", *pFunc);
}

int main(void) {
  unsigned a = 0x10203040;
  unsigned *pMain = &a;
  printf("Address of pMain %p\n", (void*)&pMain);
  printf("Address held by pMain %p\n", (void*)pMain);
  test(pMain);
  return 0;
}

https://godbolt.org/z/9a74E4nnK

Result:

Address of pMain 0x7fff2161ff30
Address held by pMain 0x7fff2161ff44
Address of pFunc 0x7fff2161ff38
Address held by pFunc 0x7fff2161ff44
Object referenced by pFunc: 0x10203040

1. pFunc is a variable local to function test. It has its own address and it holds the address kept in the pMain variable
2. pMain is a variable local to function main. It has its own address and it holds the address of the a variable.

As you see the both pointers have the same value - which is the address of the a variable.

If you want the pFunc pointer to holds the address of the pMain variable you need to declare it as pointer po pointer:

void test(unsigned **pFunc) {
    printf("Address of pFunc %p\n", (void*)&pFunc);
    printf("Address held by pFunc %p\n", (void*)pFunc);
    printf("object referenced by *pFunc %p\n", (void*)*pFunc);
    printf("Object referenced by pFunc: 0x%x\n", **pFunc);
}

int main(void) {
  unsigned a = 0x10203040;
  unsigned *pMain = &a;
  printf("Address of pMain %p\n", (void*)&pMain);
  printf("Address held by pMain %p\n", (void*)pMain);
  test(&pMain);
  return 0;
}

Result:

Address of pMain 0x7ffda335b9a8
Address held by pMain 0x7ffda335b9a4
Address of pFunc 0x7ffda335b998
Address held by pFunc 0x7ffda335b9a8
object referenced by *pFunc 0x7ffda335b9a4
Object referenced by pFunc: 0x10203040