is data shared between processes when we use fork in c?

Question

In this C program, data is not being shared between process i.e. parent and child process. child has it\'s own data and parent has it\'s own data but pointer is showing the

Answer 1

fork creates exact copy of the parent process memory image (exception see in man page). This is called Copy On Write(COW) fork. Upto time child only read data, both parent and child have same copy of data but when child write, a new copy is generated and then both child and parent have different copyies for their own data

Answer 2

When you fork a new process the new child process is a copy of the parent process. That's why pointers etc. are equal. Due to the wonders of virtual memory two processes can have the same memory map, but still be using different memory.

Answer 3

fork() creates a copy of the calling process, including all the memory allocated to it.

Each process has its own address space and the values of pointers are within context of that address space. So printing the address of some variable in the original process will give the same output as printing that address in the spawned process.

However, as far as the operating system is concerned, the addresses are not equal. The operating system takes care of ensuring each process has the illusion of its own memory.

There are means of sharing memory between processes (i.e. what one process writes to the shared memory, the other one sees). However, that is not what happens by default, and still happens with the help of the host operating system.