WOuld it be possible rather than allocating memory for the char * return that you could instead return an SV *? You could do away with the the Newz() and strcpy and end up with something like (untested):

SV *
TestStringAdd (a,b)
        char* a
        char* b


        CODE:
                char* c;
                SV* d;
                int length;
                
                c = StringAdd(a, b);

                length = strlen(c);
                
                d = newSVpv(c,length);

                // deallocate Memory
                FreeMemory (c);

                printf ("Name::%s\n", d);
                printf ("Length::%d\n", length);
                RETVAL = d;

        OUTPUT:
          RETVAL
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This will at the least save dicking around with the allocations and let perl deal with it.

/J\