Why malloc return value is not in the process memory map?

Question

I'm using OS X 10.10.5 now, and I'm doing an experiment about malloc and heap like below:

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

int main() {
    int *p;
    p = malloc(sizeof(int));
    *p = 100;
    printf("the malloc p pointer addr is %x\n", p);
    getchar();
}

the out put is the malloc p pointer addr is c3404ba0;
I think address 0xc3404ba0 is allocated by maclloc as part of the process heap.

Then I use the vmmap tool to get the memory map, the result is:

We can see that the 0xc3404ba0 is not in the heap area, but it's realy the pointer to the allocated memory. What's wrong with that?

It fix now, when I use %p instead of %x, the output is the malloc p pointer addr is 0x7fe131404ba0
and the vmmap output is:

thanks to @Alex Lop.

Looks like you are running on 64bit OS. If your program was compiled in 64bit mode then using `%x` to print the pointer will cut off the upper 32 bits. Try the same with `%p` instead and post the results. — Alex Lop., Mar 30 '16 at 07:40
using the wrong format specifier invokes **undefined behavior** http://stackoverflow.com/q/33648596/995714 http://stackoverflow.com/q/4231891/995714 http://stackoverflow.com/q/14504148/995714 http://stackoverflow.com/q/16864552/995714 — phuclv, Mar 30 '16 at 08:01

score 4 · Accepted Answer · answered Mar 30 '16 at 07:46

As I wrote in the comment, looks like you are running on 64bit OS. If your program was compiled in 64bit mode then using %x to print the pointer will cut off the upper 32 bits (since %x is used for integers). Try the same with %p instead and post the results.

My guess would be that 0xXXXXXXXXc3404ba0 belongs to that range:

Why malloc return value is not in the process memory map?

1 Answers1