null pointer in c

The NULL Pointer in C and C++

The constant NULL is a special pointer value which encodes the idea of "points to nothing." It turns out to be convenient to have a well defined pointer value which represents the idea that a pointer does not have a pointee. It is a runtime error to dereference a NULL pointer. In drawings, the value NULL is usually drawn as a diagonal line between the corners of the pointer variable's box...

The C language uses the symbol NULL for this purpose. NULL is equal to the integer constant 0, so NULL can play the role of a boolean false. Official C++ no longer uses the NULL symbolic constant — use the integer constant 0 directly. Java uses the symbol null.

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