How to use files like arrays in c OR, how to properly handle files in c ?

Question

Unlike array, if we compare a character in a file with a char variable,(using fgetc) it also increments the pointer position. How to compare, like an array , without incrementing the position ?

Also, How to know the value of a position in the file like we could use *arrayname[position] for an array ?

solutions I don't want to use and reasons :
Copy the file into an array - uses more memory.
Decrement 1 position everytime after incrementing with fgetc - less efficient.

Answer 1

Coder Kitten Thanks.
Is there any function which returns a character, like fgetc, but doesn't change the pointer ?

Answer 2

Coder Kitten So , are comparisons and other operations done by reading them first into memory ?

I am actually trying to make a program which works like this :
"grep -o 'characters[[:alnum:]]*' filename"
on linux

Answer 3

Thank you !