What is a pointer in C programming language?

A pointer in C is the address of a variable or function.

The advantages of a pointer over using normal variables are:

If you pass the pointer to a variable to a function, then that function can modify the value of the variable directly; for example, suppose you want a function to convert a string to lower case. If pointers are not available, then a function call would look like this (in BASIC):

NewString = ToLower("This Is A String")

What the BASIC compiler does is make a copy of the "This Is A String" string, pass it to the ToLower() function and return a copy back to the caller to be copied to NewString.

All these copies make the process slow. In C you can do this:

StringPtr = "This Is A String"
ToLower(StringPtr)

StringPtr points to the string, ToLower() receives the pointer and performs the conversion on the original string without any copying taking place.

Function pointers allow C to be used in a more object orientated way; C doesn't support objects, but a structure can contain a collection of data and function pointers so the structure can effectively contain data and the functions needed to process it.

The danger of pointers is that they point directly into computer memory and its impossible for the compiler to be certain that you haven't made a pointer point outside of the program memory; the way you find out is when the program crashes when run with an exception error.

There is a also slight format error with the way pointers are described in C; for example consider the following function:

int Divide(int *a, int *b)
{
int r;
r = *a/*b;
return r;
}

Although it looks harmless, the compiler can't tell if the /*b; is introducing a comment or is part of the calculation and most compilers will produce a missing close comment message - although some will silently compile the program - but commenting out everything after the *a!

1. Read more on C from : http://www.indiabix.com/c-programming/index.php
2. Read more on C Pointer from :http://www.indiabix.com/c-programming/question-answer.php?topic=nqvqmuprt