Question

Running Valgrind against an existing codebase, I am getting a lot of “Mismatched free / delete/ delete[]” errors. Many of them are a repeat of one problem: it claims that at line XXX a delete operation is being used, whereas at line YYY a malloc operation is used. However, when I open the file that it complains about and navigate to the line numbers indicated, I find that the memory was not allocated with malloc but with new. The allocated object was an standard ifstream and neither new[] nor delete[] are being used.

I’m running Valgrind 3.5. Does anyone have any idea what is happening? I cannot see how this can be a real error, but I’ve seen some people claim that Valgrind doesn’t turn up many false positives, so I want to have some confidence that this is fake before suppressing it.

Answer 1

You don’t provide a sample program, so this is a crystal-ball guess.

Your program provides an operator new but is missing an operator delete. The following sample program produces the same error message you are seeing:

#include <new>
#include <cstdlib>

/*
 * Sample program that provides `operator new`, but not `operator delete`.
 */

// minimal version of new for demonstration purpose only
void* operator new(size_t numBytes) {
  return malloc(numBytes);
}

int main () {
  int *p = new int;
  delete p;
}