_CP_str_alloc allocates space for a
CPSTR. It is the equivalent of malloc(), but returns
a CPSTR*. The expression should contain the length
of the string buffer to allocate. A 0 is returned if a failure occurs.
Syntax
CPSTR* _CP_str_alloc(int expression)
Note: The CPSTR* that _CP_str_alloc creates
must be later freed with _CP_str_free, not free().