suppose I have two processes p1, p2 and i am using the updated value of p2 in p1. So, to do this kind of operation why I need to use such a huge IPC`s ???

we can use a simple global variable for the above operations and that solves the problem.

In such case what is the use of IPC`s ?

do not demand replys "ASAP", someone will answer you as and when they feel like it.

And please actually describe your question in a useful amount of detail. If you feel you can just copy and paste the title, you're doing it wrong.

Processes run in their own, separate memory space. There is no such thing as a "global variable" shared between two processes.

You may have two processes, each running the same executable, which means each references all its variables with the same names, but each variable is unique to each process. There is no sharing.

Think of it a different way. Let's pretend what you describe is how things work. Let's take the example above (e.g. two processes running the same executable). Suppose I run process A to do task #1 and process B to do task #2. Task #1 and task #2 might require different values for the global variables to perform their respective tasks. So what happens? Task #1 and task #2 "fight" each other or get "confused" because the other process changed the value of a global variable.

If you want two processes to communicate, you must use IPC of some form.

Contrast this with threads. Threads run inside the same memory space as the process that started the thread(s). Global variables can be used for some communication between threads--because the variable name resolves to the same location in the same memory space.

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Hi All,
What are the advantages of a double pointer?
FYI,
I know some what about double pointer the below code and its functionality I know
#include<stdio.h>
#include<stdlib.h>
void double_fun(int **q)
{
*q=malloc(10);
**q=10;
}
int main()
{
int *p;
double_fun(&p);
printf("%d \n",*p);
}
Please explain some more points about the double pointer other than the above program.

expecting explanation with programs

please acknowledge the responses you have been given, don't just ask another question. And don't "expect" anything. We are volunteers here.

what if I have a volatile global variable which I want to use it for inter process communication, why do I need an IPC then ?
will it work only for single core communication ? why not for multi core communication ?