c++ - Valgrind 8 bytes inside a block of 16 free'd -

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i'm writing code lab in class, exercise in ood design using circular linked list. means few key functions used aren't accessible me. however, i'm confused because although driver mimics 1 written professor, i'm still getting mchk error in title. here code references

{ int nnodesfreed{0}; node* n{head};  for(; n!= head || ! nnodesfreed; n = n->next) {     delete n;     nnodesfreed++;     } cout << "# nodes freed: " << nnodesfreed << endl; }

i saw in similar question problem i'm trying access memory has been freed. i.e. how can n = n->next if n doesn't exist anymore. tried switching while loop using current , next pointer, made problem worse. code works in professor's version of assignment, in haven't implemented functions need to.

the exact error i'm given is:

invalid read of size 8    @ 0x400d8a: main (lab04.cpp:28) // references loop address 0x5a02048 8 bytes inside block of size 16 free'd   @ 0x4c28fac: operator delete(void*)    0x400d81: main (lab04.cpp:29)

thanks

you accessing n after has been deleted. causing undefined behavior.

further, you're not checking n->next valid: deleted head in first iteration. deleting n cause head updated? if not, you'll reach undefined behavior again when reach end of linked list (which may caused either deleteing nullptr or else deleteing garbage pointer (depending on n->next on end of linked list points to).


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