why does the hexadecimal value of pointer address returned is always in decreasing order?
for example here int a was declared before int d, so it's address always comes out to be greater than d, and same for &b,&e and &c,&f, I want to know that is this a fixed behavior or is this compiler dependent?
I am using gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-1)
#include<stdio.h>
int main(void){
int a=1;
int d=1;
char b='a' ;
char e='a';
float c=1.0;
float f=1.0;
printf("a=%p\nd=%p\nb=%p\ne=%p\nc=%p\nf=%p\n",&a,&d,&b,&e,&c,&f);
if (&a>&d)
printf("&a>&d\n");
else
{printf("&a<&d");
}
if (&a>&d && &b>&e && &c>&f)
printf("addresses are in descending order");
else{
printf("false");
}
return 0;
}
output:
a=0xbfc6bd98 //a>d
d=0xbfc6bd94
b=0xbfc6bd9f //b>e
e=0xbfc6bd9e
c=0xbfc6bd90 //c>f
f=0xbfc6bd8c
&a>&d
addresses are in descending order
PS: I am new to c
Found this nicely explained in Smashing The Stack For Fun And Profit, by Aleph One. Extracted the most relevant parts.
/------------------\ lower | | memory | Text | addresses | | |------------------| | (Initialized) | | Data | | (Uninitialized) | |------------------| | | | Stack | higher | | memory \------------------/ addresses Fig. 1 Process Memory Regions
[...]
The stack consists of logical stack frames that are pushed when calling a function and popped when returning. A stack frame contains the parameters to a function, its local variables, and the data necessary to recover the previous stack frame, including the value of the instruction pointer at the time of the function call. Depending on the implementation the stack will either grow down (towards lower memory addresses), or up. In our examples we'll use a stack that grows down. This is the way the stack grows on many computers including the Intel, Motorola, SPARC and MIPS processors.
[...]
Let us see what the stack looks like in a simple example: example1.c: ------------------------------------------------------------------------------ void function(int a, int b, int c) { char buffer1[5]; char buffer2[10]; } void main() { function(1,2,3); } ------------------------------------------------------------------------------
[...]
With that in mind our stack looks like this when function() is called (each space represents a byte): bottom of top of memory memory buffer2 buffer1 sfp ret a b c <------ [ ][ ][ ][ ][ ][ ][ ] top of bottom of stack stack
As you can see, new (local) variables are pushed on top of the stack. Depending on the design of the architecture the stack grows towards higher memory addresses or towards lower memory addresses, the latter in your case.
From the viewpoint of the C language specification the order of memory locations of subsequently allocated variables is unspecified. Therefore, it depends ...