When the requested size is zero the behavior of the memory allocation functions malloc(), calloc(), and realloc() is implementation-defined. Section 7.22.3 of the C standard [ISO/IEC 9899:2011] states:
If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.
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