动态分配包含动态分配数组的结构数组

Question

我正在尝试从 XML 文件中读取设置值，为了使事情更简单，我设置了一个包含每个值的结构。其中之一是结构数组。然后我将结构初始化为数组。

在运行编译代码时，我有时会很顺利运行，有时会出现段错误，有时会出现中止陷阱 (malloc: *** error for object: incorrect checksum for freed object - object was probably modified after being freed. *** set a breakpoint in malloc_error_break to debug Abort trap: 6)。我想这是未定义的行为。

我可能对为什么会发生这种情况有所暗示，但我无法得到任何确认，尽管我进行了大量研究。

在我看来，这是由于 space 为结构数组分配了足够的内存以包含具有一些值的结构和一个空结构数组引起的。然后我为第二个结构数组分配内存，因此更改第一个结构数组所需的 space。

这些是结构的声明：

struct Delegate {

  int warnings;

  gchar *name;

};

struct Staff {

  gchar *president;
  gchar *vice;
  gchar *mod;

};

struct Committee {

  int n_delegate;

  gchar *name;
  gchar *topics[2];

  struct Delegate *delegates;
  struct Staff staff;


};

这是我正在尝试的代码运行:

static void load_prop() {

  xmlDocPtr doc;
  xmlNodePtr node;
  xmlNodePtr subnode;
  xmlNodePtr subsubnode;
  xmlNodePtr subsubsubnode;
  xmlChar *cnumber;

  doc = xmlParseFile("/Users/username/Documents/Obermun/DebateProgram/res/xml/property.xml");
  node = xmlDocGetRootElement(doc);

  edition = (char *) xmlGetProp(node, (const xmlChar *) "edition");

  int const index = atoi((const char*)(xmlGetProp(node, (const xmlChar *) "committees")));
  committees = (Committee *) malloc(sizeof(Committee)*index);

  subnode = node -> xmlChildrenNode;
  int i = 0;
  int t = 0;
  int d = 0;

  while(subnode != NULL) {

    if(!xmlStrcmp(subnode -> name, (const xmlChar *) "committee")) {

      committees[i].name = (char *) xmlGetProp(subnode, (const xmlChar *) "name");
      committees[i].n_delegate = atoi((const char*) xmlGetProp(subnode, (const xmlChar *) "delegates"));
      committees[i].delegates = (Delegate *) malloc(sizeof(Delegate)*committees[i].n_delegate);

      subsubnode = subnode -> xmlChildrenNode;

      while(subsubnode != NULL) {

        if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "topic")) {

          committees[i].topics[t] = (char *) xmlNodeListGetString(doc, subsubnode -> xmlChildrenNode, 1);
          t++;

        }

        else if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "delegate")) {

          committees[i].delegates[d].warnings = atoi((const char*) xmlGetProp(subsubnode, (const xmlChar *) "warnings"));
          committees[i].delegates[d].name = (char *) xmlNodeListGetString(doc, subsubnode -> xmlChildrenNode, 1);
          d++;

        }

        else if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "staff")) {

          subsubsubnode = subsubnode -> xmlChildrenNode;

          while(subsubsubnode != NULL) {

            if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "president")) {

              committees[i].staff.president = (char *) xmlNodeListGetString(doc, subsubsubnode -> xmlChildrenNode, 1);

            }

            if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "vice")) {

              committees[i].staff.vice = (char *) xmlNodeListGetString(doc, subsubsubnode -> xmlChildrenNode, 1);

            }

            if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "mod")) {

              committees[i].staff.mod = (char *) xmlNodeListGetString(doc, subsubsubnode -> xmlChildrenNode, 1);

            }

            subsubsubnode = subsubsubnode -> next;

          }

        }

        subsubnode = subsubnode -> next;

      }

      i++;

    }

    subnode = subnode -> next;

  }

}

尝试使用 gdb 调试代码我得到了这个回溯：

Thread 2 received signal SIGABRT, Aborted.
0x00007fff7353ab66 in ?? () from /usr/lib/system/libsystem_kernel.dylib
(gdb) bt
#0  0x00007fff7353ab66 in ?? () from /usr/lib/system/libsystem_kernel.dylib
#1  0x00007fff73705080 in pthread_kill () from /usr/lib/system/libsystem_pthread.dylib
#2  0x00007fff734961ae in abort () from /usr/lib/system/libsystem_c.dylib
#3  0x0000003000000010 in ?? ()
#4  0x00007ffeffffffdf in ?? ()
#5  0xffffffff0160f658 in ?? ()
#6  0x000000010160f658 in ?? ()
#7  0x00007ffeefbff5f0 in ?? ()
#8  0x00007fff7359fb58 in szone_error () from /usr/lib/system/libsystem_malloc.dylib
Backtrace stopped: frame did not save the PC

Answer 1

正如@nwellnhof 在评论中指出的那样，此代码片段的问题在于我用来存储委托和主题值的变量 d 和 t 永远不会重置为 0，所以他们成长的每个周期，都试图将值存储在未分配的内存中space，导致未定义的行为。

正确的代码如下：

static void load_prop() {

  xmlDocPtr doc;
  xmlNodePtr node;
  xmlNodePtr subnode;
  xmlNodePtr subsubnode;
  xmlNodePtr subsubsubnode;
  xmlChar *cnumber;

  doc = xmlParseFile("/Users/username/Documents/Obermun/DebateProgram/res/xml/property.xml");
  node = xmlDocGetRootElement(doc);

  edition = (char *) xmlGetProp(node, (const xmlChar *) "edition");

  int const index = atoi((const char*)(xmlGetProp(node, (const xmlChar *) "committees")));
  committees = (struct Committee *) malloc(sizeof(struct Committee)*index);

  subnode = node -> xmlChildrenNode;
  int i = 0;
  int t = 0;
  int d = 0;

  while(subnode != NULL) {

    if(!xmlStrcmp(subnode -> name, (const xmlChar *) "committee")) {

      committees[i].name = strdup((char *) xmlGetProp(subnode, (const xmlChar *) "name"));
      committees[i].n_delegate = atoi((const char*) xmlGetProp(subnode, (const xmlChar *) "delegates"));
      committees[i].delegates = (struct Delegate *) malloc(sizeof(struct Delegate)*committees[i].n_delegate);

      subsubnode = subnode -> xmlChildrenNode;

      t = 0;
      d = 0;

      while(subsubnode != NULL) {

        if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "topic")) {

          committees[i].topics[t] = strdup((char *) xmlNodeListGetString(doc, subsubnode -> xmlChildrenNode, 1));
          t++;

        }

        else if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "delegate")) {

          committees[i].delegates[d].warnings = atoi((const char*) xmlGetProp(subsubnode, (const xmlChar *) "warnings"));
          committees[i].delegates[d].name = strdup((char *) xmlNodeListGetString(doc, subsubnode -> xmlChildrenNode, 1));
          d++;

        }

        else if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "staff")) {

          subsubsubnode = subsubnode -> xmlChildrenNode;

          while(subsubsubnode != NULL) {

            if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "president")) {

              committees[i].staff.president = strdup((char *) xmlNodeListGetString(doc, subsubsubnode -> xmlChildrenNode, 1));

            }

            if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "vice")) {

              committees[i].staff.vice = strdup((char *) xmlNodeListGetString(doc, subsubsubnode -> xmlChildrenNode, 1));

            }

            if(!xmlStrcmp(subsubnode -> name, (const xmlChar *) "mod")) {

              committees[i].staff.mod = strdup((char *) xmlNodeListGetString(doc, subsubsubnode -> xmlChildrenNode, 1));

            }

            subsubsubnode = subsubsubnode -> next;

          }

        }

        subsubnode = subsubnode -> next;

      }

      i++;

    }

    subnode = subnode -> next;

  }

}

注意 t 和 d 在每个循环之前被设置为 0。

动态分配包含动态分配数组的结构数组

Dynamically allocate an array of struct containing a dynamically allocated array

c

arrays

struct

malloc

libxml2