According to the C standard [ISO/IEC 9899-2011], the behavior of a program that uses the value of a pointer that refers to space deallocated by a call to the free() or realloc() function is undefined. (See undefined behavior 168 of Annex J.)
Reading a pointer to deallocated memory is undefined because the pointer value is indeterminate and and can have a trap representation. In the latter case, doing so may cause a hardware trap.
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