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C-赋值后访问struct属性导致分段错误

segmentation-fault linked-list struct c

Henry Williams · 技术社区 · 7 年前

我有两个结构:wires和wireLLN(导线的链表节点)。其思想是,findWire()函数在链表中查找具有与给定导线同名导线(wireName)的节点。添加第一条导线时,这不会出现任何问题,因为头部节点为null,因此将使用导线作为节点的“导线”属性创建一个新节点。addNode中的printf调用显示了这一点。但是,在第二次运行findWire()时,尝试访问head节点的“wire”属性会导致分段错误。(我已经对代码中出现segfault的位置进行了注释)

typedef struct wires {
  bool value;
  char* name;
} Wire;

typedef struct wireLLN {
  Wire wire;
  struct wireLLN * nextNode;
} WireLLN;

//head of the linked list
WireLLN * headWire = NULL;

// adds a node to the linked list
void addNode(WireLLN* head, WireLLN* node){
  if (headWire == NULL){
    headWire = node;
        printf("Head node was null. Adding node with wire name: %s\n", headWire->wire.name); //this prints no problem
    }
  else if (head->nextNode == NULL)
    head->nextNode = node;
  else
    addNode(head->nextNode, node);
}

//finds if a wire with a given name already exists, if not returns null
Wire * findWire(char wireName[], WireLLN * head){
  if (headWire != NULL){
        puts("head wasnt null");
        printf("HEAD NODE ADDRESS: %s\n", head);
        printf("HEAD WIRE: %s\n", head->wire); //SEG FAULT HERE
    if (strcmp(head->wire.name, wireName) == 0){
            puts("1");
            return &head->wire;
        } else if (head->nextNode == NULL){
            puts("2");
            return NULL;
        } else {
            puts("3");
            return findWire(wireName, head->nextNode);
        }
  } else return NULL;
}


// assigns a wire to a gate if it exists, otherwise creates a new one then assigns it
Wire assignWire(char wireName[]){
  Wire * result = findWire(wireName, headWire);
  if (result == NULL){
    Wire wire = makeWire(wireName);
    WireLLN node;
    node.wire = wire;
    addNode(headWire, &node);
    return wire;
  } else {
    return *result;
  }
}

谢谢你的时间。

1 回复 | 直到 7 年前

GRASBOCK 7 年前

内存释放问题。Yoiu忘记了一旦函数停止运行,内存将被删除。这在assignwire函数中发生。

您可能希望将其更改为:

Wire assignWire(char wireName[]){
  Wire * result = findWire(wireName, headWire);
  if (result == NULL){
    //to prevent the data being lost after the function returns
    WireLLN* node = (WireLLN*)malloc(sizeof(WireLLN));
    node->wire = makeWire(wireName);
    addNode(headWire, node);
    return node->wire;
  } else {
    return *result;
  }
}

空检查没有警告您的原因是,您给addNode的指针在函数返回后停止分配内存。然后您访问该内存(地址相同),但它不是允许您写入任何内容的内存。

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