What are all the common undefined behaviours that a C++ programmer should know about? [closed]

Dereferencing a NULL pointer
Dereferencing a pointer returned by a “new” allocation of size zero
Using pointers to objects whose lifetime has ended (for instance, stack allocated objects or deleted objects)
Dereferencing a pointer that has not yet been definitely initialized
Performing pointer arithmetic that yields a result outside the boundaries (either above or below) of an array.
Dereferencing the pointer at a location beyond the end of an array.
Converting pointers to objects of incompatible types
Using memcpy to copy overlapping buffers.

Reading or writing to an object or array at an offset that is negative, or beyond the size of that object (stack/heap overflow)

Signed integer overflow
Evaluating an expression that is not mathematically defined
Left-shifting values by a negative amount (right shifts by negative amounts are implementation defined)
Shifting values by an amount greater than or equal to the number of bits in the number (e.g. int64_t i = 1; i <<= 72 is undefined)

Casting a numeric value into a value that can’t be represented by the target type (either directly or via static_cast)
Using an automatic variable before it has been definitely assigned (e.g., int i; i++; cout << i;)
Using the value of any object of type other than volatile or sig_atomic_t at the receipt of a signal
Attempting to modify a string literal or any other const object during its lifetime
Concatenating a narrow with a wide string literal during preprocessing

Not returning a value from a value-returning function (directly or by flowing off from a try-block)
Multiple different definitions for the same entity (class, template, enumeration, inline function, static member function, etc.)
Infinite recursion in the instantiation of templates
Calling a function using different parameters or linkage to the parameters and linkage that the function is defined as using.

Cascading destructions of objects with static storage duration
The result of assigning to partially overlapping objects
Recursively re-entering a function during the initialization of its static objects
Making virtual function calls to pure virtual functions of an object from its constructor or destructor
Referring to nonstatic members of objects that have not been constructed or have already been destructed

A non-empty source file that doesn’t end with a newline, or ends with a backslash (prior to C++11)
A backslash followed by a character that is not part of the specified escape codes in a character or string constant (this is implementation-defined in C++11).
Exceeding implementation limits (number of nested blocks, number of functions in a program, available stack space …)
Preprocessor numeric values that can’t be represented by a long int
Preprocessing directive on the left side of a function-like macro definition
Dynamically generating the defined token in a #if expression