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Dereferencing a null pointer

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This is an example of dereferencing a NULL pointer, causing undefined behavior. 

int * pointer = NULL;
int value = *pointer; /* Dereferencing happens here */

A NULL pointer is guaranteed by the C standard to compare unequal to any pointer to a valid object, and dereferencing it invokes undefined behavior.

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Undefined behavior:
* Undefined behavior
* Dereferencing a pointer to variable beyond its lifetime
* Copying overlapping memory
* Signed integer overflow
* Use of an uninitialized variable
* Read value of pointer that was freed
* Data race
* Modify string literal
* Using incorrect format specifier in printf
* Modifying any object more than once between two sequence points
* Passing a null pointer to printf s conversion
* Bit shifting using negative counts or beyond the width of the type
* Freeing memory twice
* Accessing memory beyond allocated chunk
* Returning from a function thats declared with Noreturn or noreturn function specifier
* Addition or subtraction of pointer not properly bounded
* Modifying a const variable using a pointer
* Dereferencing a null pointer
* Reading an uninitialized object that is not backed by memory
* Using fflush on an input stream
* Division by zero
* Missing return statement in value returning function
* Inconsistent linkage of identifiers
* Conversion between pointer types produces incorrectly aligned result
* Modifying the string returned by getenv strerror and setlocale functions
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