Question

我在C中实现了一个基本的BST。虽然我在使用Memcheck时遇到错误，但似乎我的插入功能正常工作，如：

==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009EF: bst_insert (bst.c:45)
==7839==    by 0x400A0D: bst_insert (bst.c:65)
==7839==    by 0x4007A5: main (bst-test.c:22)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009EF: bst_insert (bst.c:45)
==7839==    by 0x400A2B: bst_insert (bst.c:61)
==7839==    by 0x4007B2: main (bst-test.c:23)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009EF: bst_insert (bst.c:45)
==7839==    by 0x400A0D: bst_insert (bst.c:65)
==7839==    by 0x400A0D: bst_insert (bst.c:65)
==7839==    by 0x4007BF: main (bst-test.c:24)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009EF: bst_insert (bst.c:45)
==7839==    by 0x400A2B: bst_insert (bst.c:61)
==7839==    by 0x400A0D: bst_insert (bst.c:65)
==7839==    by 0x4007CC: main (bst-test.c:25)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009EF: bst_insert (bst.c:45)
==7839==    by 0x400A0D: bst_insert (bst.c:65)
==7839==    by 0x400A2B: bst_insert (bst.c:61)
==7839==    by 0x4007D9: main (bst-test.c:26)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009EF: bst_insert (bst.c:45)
==7839==    by 0x400A2B: bst_insert (bst.c:61)
==7839==    by 0x400A2B: bst_insert (bst.c:61)
==7839==    by 0x4007E6: main (bst-test.c:27)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009AF: bst_inorder (bst.c:30)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x400807: main (bst-test.c:29)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009D0: bst_inorder (bst.c:30)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x400807: main (bst-test.c:29)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009AF: bst_inorder (bst.c:30)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x400807: main (bst-test.c:29)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009D0: bst_inorder (bst.c:30)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x400807: main (bst-test.c:29)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009AF: bst_inorder (bst.c:30)
==7839==    by 0x4009C3: bst_inorder (bst.c:35)
==7839==    by 0x400807: main (bst-test.c:29)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x4009D0: bst_inorder (bst.c:30)
==7839==    by 0x400807: main (bst-test.c:29)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400A7F: bst_preorder (bst.c:77)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400825: main (bst-test.c:31)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400AA0: bst_preorder (bst.c:77)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400825: main (bst-test.c:31)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400A7F: bst_preorder (bst.c:77)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400825: main (bst-test.c:31)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400AA0: bst_preorder (bst.c:77)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400825: main (bst-test.c:31)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400A7F: bst_preorder (bst.c:77)
==7839==    by 0x400A98: bst_preorder (bst.c:84)
==7839==    by 0x400825: main (bst-test.c:31)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400AA0: bst_preorder (bst.c:77)
==7839==    by 0x400825: main (bst-test.c:31)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400AD4: bst_search (bst.c:91)
==7839==    by 0x400B38: dosearch (bst-test.c:10)
==7839==    by 0x400850: main (bst-test.c:34)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400AD4: bst_search (bst.c:91)
==7839==    by 0x400B38: dosearch (bst-test.c:10)
==7839==    by 0x40085D: main (bst-test.c:35)
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400dfe is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400d9f is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400da3 is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400de5 is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400da1 is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400da5 is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Invalid free() / delete / delete[] / realloc()
==7839==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7839==    by 0x400980: bst_free (bst.c:21)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839==  Address 0x400da7 is not stack'd, malloc'd or (recently) free'd
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400989: bst_free (bst.c:22)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== Conditional jump or move depends on uninitialised value(s)
==7839==    at 0x400977: bst_free (bst.c:17)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x400992: bst_free (bst.c:23)
==7839==    by 0x40087F: main (bst-test.c:38)
==7839== 
==7839== 
==7839== HEAP SUMMARY:
==7839==     in use at exit: 224 bytes in 14 blocks
==7839==   total heap usage: 14 allocs, 7 frees, 224 bytes allocated
==7839== 
==7839== LEAK SUMMARY:
==7839==    definitely lost: 80 bytes in 8 blocks
==7839==    indirectly lost: 144 bytes in 6 blocks
==7839==      possibly lost: 0 bytes in 0 blocks
==7839==    still reachable: 0 bytes in 0 blocks
==7839==         suppressed: 0 bytes in 0 blocks
==7839== Rerun with --leak-check=full to see details of leaked memory
==7839== 
==7839== For counts of detected and suppressed errors, rerun with: -v
==7839== Use --track-origins=yes to see where uninitialised values come from
==7839== ERROR SUMMARY: 39 errors from 35 contexts (suppressed: 0 from 0)

这是我的实施：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "mylib.h"
#include "bst.h"

struct bstnode {

  char *key;
  bst left;
  bst right;

};

bst bst_free(bst b) {

  if (b == NULL) {

    return b;
  }
  free(b->key);
  bst_free(b->left);
  bst_free(b->right);

  return b;
}

void bst_inorder(bst b, void f(char *str)) {

  if (NULL == b) {

    return;
  }

  bst_inorder(b->left, f);

  f(b->key);

  bst_inorder(b->right, f);

}

bst bst_insert(bst b, char *str) {

  if (b == NULL) {

    bst result = emalloc(sizeof *result);
    result->key = str;

    return result;
  }

  if (strcmp(b->key, str) == 0) {

    return b;
  }

  if (strcmp(b->key, str) < 0) {

    b->right = bst_insert(b->right, str);
    return b;
  }

  b->left = bst_insert(b->left, str);
  return b;

}

bst bst_new() {

  return NULL;
}

void bst_preorder(bst b, void f(char *str)) {

  if (NULL == b) {

    return;
  }

  f(b->key);

  bst_preorder(b->left, f);
  bst_preorder(b->right, f);

}

int bst_search(bst b, char *str) {

  if (NULL == b) {

    return 0;
  }

  if (strcmp(b->key, str) == 0) {

    return 1;
  }

  if (strcmp(b->key, str) < 0) {

    return bst_search(b->right, str);
  }

  return bst_search(b->left, str);

}

我有另一个文件只测试它，我的输出是按预期的，但我不太清楚为什么我收到这些消息。这是我用来检查我的BST的文件：

#include <stdio.h>
#include <stdlib.h>
#include "bst.h"

void print_key(char *key) {
  printf("%s\n", key);
}

void dosearch(bst b, char *key) {
  if (bst_search(b, key) == 0) {
    printf("%s -- not found\n", key);
  } else {
    printf("%s -- found\n", key);
  }
}

int main(void) {

  bst b = bst_new();
  printf("inserting d,b,f,a,c,e,g\n");
  b = bst_insert(b, "d");
  b = bst_insert(b, "b");
  b = bst_insert(b, "f");
  b = bst_insert(b, "a");
  b = bst_insert(b, "c");
  b = bst_insert(b, "e");
  b = bst_insert(b, "g");
  printf("inorder traversal\n");
  bst_inorder(b, print_key);
  printf("preorder traversal\n");
  bst_preorder(b, print_key);
  printf("searching\n");
  dosearch(b, "f");
  dosearch(b, "o");
  dosearch(b, "x");
  dosearch(b, "e");
  dosearch(b, "d");
  bst_free(b);
  return EXIT_SUCCESS;

}

Answer 1

虽然我不知道您使用的这个emalloc函数，但普通malloc不会初始化它分配的内存，这意味着left和right指针不会被初始化。使用这些未初始化的指针会导致undefined behavior。

解决方案？只需在分配后将这些指针设置为NULL。

Answer 2

我猜您将'bst'定义如下：

typedef struct bstnode *bst;

我认为bst_insert（）存在问题你只为bst_node的指针变量分配内存。

bst result = emalloc(sizeof *result);

你必须为bst_node本身和bst_node的密钥分配内存以下代码是解决问题的部分原因。

bst bst_insert(bst b, char *str) {
    if (b == NULL) {
    {
        bst result = emalloc(sizeof(struct bstnode));
        result->left = null;
        result->right = null;
        result->key = emalloc(strlen(str) + 1);
        strcpy(result->key, str);

        return result;
    }
    .....
}

二进制搜索树内存错误

2 个答案: