CODEWITHSUNDEEP
c++
Gautam Kumar
Gautam Kumar

Reputation: 1170

Locations for different program elements

Where are pointer variables and functions located?

Upvotes: 0

Views: 81

Answers (2)

Employed Russian
Employed Russian

Reputation: 213375

Functions are in .text section.

Pointers are wherever: local pointers on stack, global/static points in .bss, etc.

Yes, an automatic (on stack) pointer could point anywhere (or nowhere at all):

void foo() {
   char *p = NULL;               // this pointer points nowhere
   const char *q = "hello";      // points to read-only constant
   char buf[1], *r = buf;        // r points to stack
}

There is no difference between pointers and other kinds of variables; just as buf above ends when foo() returns, so do p, q and r.

Also note that that lifetime of the pointer, and the lifetime of the entity it points at have nothing to do with each other. A pointer may have shorter, same, or longer lifetime than the pointed-at entity (and this is a rich source of bugs in C and C++). Some examples:

int *gp1, *gp2, *gp3;
void foo() {
  int j;
  int *lp1, *lp2, *lp3;

  gp1 = lp1 = &j;      // both global 'gp1' and local 'lp1' point to local 'j'
  gp2 = lp2 = new int; // 'gp2' and 'lp2' point to dynamically allocated
                       // anonymous 'int'
  if (true) {
    int j2;
    gp3 = lp3 = &j2;
  }
  // 'gp3' and 'lp3' are "dangling" -- point to 'j2' which no longer exists.
}

Once foo returns, gp1, gp2 and gp3 all still exist, but only gp2 points to valid memory.

Upvotes: 4

Summer_More_More_Tea
Summer_More_More_Tea

Reputation: 13346

Pointer variables have not different to data variables. And functions are your real program, function name will be converted to an internal symbol after compiled used to locate an address in memory where the function body begins and function body will be compiled to assembles, machine code eventually.

=================================================================================

[Edit for the Second Question]

As I pointed out, pointer variables have no different to data variables, including the storage and lifetime. e.g. This is an example .cpp file

#include <stdio.h>
#include <stdlib.h>

using namespace std;

int I_m_data = 10;

int *I_m_global;
int *I_m_initialized = &I_m_data;

int main(){
    int *I_m_local = NULL;

    int **dynamic_allocated = (int **)malloc(sizeof(int *));

    free(dynamic_allocated);
}

Here, I_m_global is in .bss section, I_m_initialized is in .data section, I_m_local is on stack, and pointer pointed by dynamic_allocated is on heap while dynamic_allocated itself is on stack.

Besides, I_m_global and I_m_initialized have global lifetime; I_m_local and dynamic_allocated cannot be indexed out of main. Remember free heap space pointed by dynamic_allocated manually in case of memory leak.

Good luck!

Upvotes: 1

Related Questions