All the segments are used
for specific purpose. Like segment number 15 is used for ROM, segment number 14
is used for BIOS etc.
We will discuss about how to access text video
memory, graphics video memory in the pointer and union chapters of 255 bits
color graphics programming.
1. Stack area
All automatic variables and constants are stored
into stack area. Automatic variables and constants in c:
1.
All the local variables of default storage
class.
2.
Variables of storage calls auto.
3.
Integer constants, character constants, string
constants, float constants etc in any expression.
4.
Function parameters and function return value.
Variables in the stack area are always deleted when
program control reaches it out of scope. Due to this stack area is also called
temporary memory area. For example:
What will be output of
following c code?
#include<stdio.h>
int main(){
int i;
for(i=0;i<3;i++){
int a=5;
printf("%d",a);
}
return 0;
}
Output:
5 5 5
Explanation:
Since variable a is automatic
variable, it will store in the stack area. Scope of variable a is within for loop. So after each
iteration variable a will be deleted from stack and in each iteration variable
a will initialize.
This two concepts are only for Turbo C 3.0
It follows LIFO data structure. That in the stack
area of memory data is stored in last in first out. For example:
What will be output of
flowing c code. (Turbo c 3.0)?
#include<stdio.h>
int main(){
int a =5, b = 6, c = 7,d =8;
printf("%d %d %d");
return 0;
}
Output: 8 7 6
Explanation:
Default storage class of variables a, b, c and d is
auto .Since it automatic variable it will be sorted in the stack area of memory.
It will store in the stack as
Stack always follows LIFO data structure. In the
printf function, name of variables is not written explicitly. So default output
will content of stack which will be in the LIFO order i.e. 8 7 6.
It has two part one for initialize variable another
for non-initialize variable. All initialize variables are more nearer than not initialized
variable and vice versa. For example:
What will be output of
following program (Turbo c 3.0)?
#include<stdio.h>
int main(){
int a =5, b, c =7;
printf("%d %d %d");
return 0;
}
Output: 7 5 garbage value
Explanation:
Automatic variable a and c has initialized while b
has not initialized. Initialize variables are more nearer than uninitialized
variable .They will be stored in the stack. So due to LIFO first output will be
7 then 6 (since a is more nearer than b with respect to c) then any garbage
value will be output which is present in the stack.
Note: Default storage class
of any local variable is auto.
2. Data area:
All static and extern variable are stored in the
data area. It is permanent memory space and variable will store in the memory unless
and until program end. For example:
What will be output of
following c code?
#include<stdio.h>
int main(){
int i;
for(i=0;i<3;i++){
static int a=5;
printf("%d",a);
}
return 0;
}
Output: 5 6 7
3. Heap area:
This memory area is use to allocate memory
dynamically. In c we can allocate the memory space dynamically by using
function malloc and calloc. It always allocates memory in the heap area. Its
size is variable and depends upon free space in the memory.
4. Code area:
Function pointer can only access code area. Size of
this area is always fixed and it is read only memory area.
15 comments:
in data area program you should write a++ after the printf statement then only output 5 6 7
In the above data segment example code should be..
#include
int main(){
int i;
for(i=0;i<3;i++){
static int a=5;
printf("%d",a++);
}
return 0;
}
#include
int main(){
int i;
for(i=0;i<3;i++){
static int a=5;
printf("%d",a);
}
return 0;
}
OUTPUT is 5 5 5
#include
int main(){
int i;
for(i=0;i<3;i++){
static int a=5;
printf("%d",a);
}
return 0;
}
for this program output is: 5 5 5
can any one explain how the Function pointer can access the code area with example .............
thanks in advance
add the a++; after the printf() statement the the output is 5,6,7
Please expalin how the code area is read only and what is actually meant by function pointer can access only code area
function pointer is similar to the instruction pointer we use in assembly programming...
#include
int *call();
void main(){
int *ptr;
ptr=call();
fflush(stderr);
printf("%d",*ptr);
}
int * call(){
static int x=25;
x++;
return &x;
}
Good explanations my placement fears are no more. Thanks a lot. Keep up the good work.
yes you are ri8 cherry..
Superb explanation.. easily understandable thanks alot
are constants really stored at STACK? some other document mentioned that it's stored at data segment. Can somebody clarify?
where the pointers exactly stored ?
gud explaination
pls anyone help me where pointers are store
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