valgrind 显示内存泄漏。 我如何阻止泄漏？

Question

I'm new to valgrind and I ran it with some code I wrote for a quadtree.

I've written a function that recursively frees the Nodes from the quadtree:

void destroyTree (Node* p)
{
    if (!p) return;

    for (size_t i = 0; i < 4; ++i)
        destroyTree(p->child[i]);

    free(p);
}

I call that function in the main function:

int main( int argc, char **argv ) {

  Node *head;

  // make the head node
  head = makeNode( 0.0,0.0, 0 );

  // make a tree
  makeChildren( head );
  makeChildren( head->child[0] );
  makeChildren( head->child[1] );
  makeChildren( head->child[2] );
  makeChildren( head->child[3] );

  // print the tree for Gnuplot
    writeTree( head );
  return 0;

  //destroy tree
  destroyTree (head);
  return 0;
}

When I run valgrind its showing that I lose some memory.

The structure is:

struct qnode {
  int level;
  double xy[2];
  struct qnode *child[4];
};
typedef struct qnode Node;

I call malloc in buildTree:

Node *makeNode( double x, double y, int level ) {

  int i;

  Node *node = (Node *)malloc(sizeof(Node));

  node->level = level;

  node->xy[0] = x;
  node->xy[1] = y;

  for( i=0;i<4;++i )
    node->child[i] = NULL;

  return node;
}

How do I stop the leak? Is there something wrong with my freeing function or is it somewhere else?

Answer 1

okay, since noone spotted this, the end of main reads:

  // print the tree for Gnuplot
    writeTree( head );
  return 0;    // <----------- wooooot!

  //destroy tree
  destroyTree (head);
  return 0;
}

We notice that the 2 last lines are unreacheable because there's a return 0 statement just above this. So the destroyTree method is never called, which explains the memory leak.

Always enable compiler warnings and read them . The control flow is simple enough, every compiler detects dead code here.

That said, even -Wall -Wextra doesn't work here, the -Wunreachable-code flag must be added explicitly ( Why does GCC not warn for unreachable code? )