C++ skip list implementation - returned value is corrupted, memory leak?

Question

I want to implement skip list, my code is not full and it needs some more functions and variables, but I am at this level of developing it and I ran into problems already.

The lines 160 and 133 should give back the same value, in this example a 5, but somehow it gets corrupted and 160 returns some strange integer (I guess it accesses some memory that is not allocated)

I ran valgrind and got following:

height insert 5
b.second 5
==9440== Conditional jump or move depends on uninitialised value(s)
==9440==    at 0x40C21BD: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40C2502: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CDEBB: std::ostream& std::ostream::_M_insert<long>(long) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CE042: std::ostream::operator<<(int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x41654D2: (below main) (libc-start.c:226)
==9440== 
==9440== Use of uninitialised value of size 4
==9440==    at 0x40C1C53: ??? (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40C21F0: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40C2502: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CDEBB: std::ostream& std::ostream::_M_insert<long>(long) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CE042: std::ostream::operator<<(int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x41654D2: (below main) (libc-start.c:226)
==9440== 
==9440== Conditional jump or move depends on uninitialised value(s)
==9440==    at 0x40C1C5C: ??? (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40C21F0: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40C2502: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CDEBB: std::ostream& std::ostream::_M_insert<long>(long) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CE042: std::ostream::operator<<(int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x41654D2: (below main) (libc-start.c:226)
==9440== 
==9440== Conditional jump or move depends on uninitialised value(s)
==9440==    at 0x40C221A: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40C2502: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, long) const (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CDEBB: std::ostream& std::ostream::_M_insert<long>(long) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x40CE042: std::ostream::operator<<(int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==9440==    by 0x41654D2: (below main) (libc-start.c:226)
==9440== 
find main 68678181

I know I need to delete Car-Objects, but I will do it somewhere at the end of the programm and I do not believe that it is the cause of the problem.

It would be good if somebody could show me my errors and why my variable gets corrupted.

Thanks in adavnce

Answer 1

The return value is uninitialized because your find method is recursive. You are not propagating the final call's result back up to the main method.

In fact, your compiler should be warning you that your find method has paths that do not return a value. For instance, if r==NULL and (*anf).down !=NULL, then you will eventually fall down to the end of the method and not return anything.