尝试将struct传递给函数时保持segfaulting [英] Keep segfaulting when trying to pass struct into function

问题描述

  void createQueue（struct pqueue * queue）
我试图将一个指向队列的指针传递给createQueue函数： ）{
 queue = malloc（sizeof（struct pqueue））; 
 queue-> root = malloc（sizeof（struct node））; 
 queue-> root-> next = 0; 
 queue-> root-> taskID = 12; 
 queue-> root-> priority = 5000; 
} 
  

我也尝试添加新创建的队列，如下所示：

  void add（struct pqueue * queue，int taskID，int priority）{
 struct node * conductor; 
 conductor = queue-> root; 
 if（conductor！= 0）{
 while（conductor-> next！= 0）
 {
 conductor = conductor-> next; 
} 
} 
 conductor-> next = malloc（sizeof（struct node））; 
 conductor = conductor->下; 
 if（conductor == 0）
 {
 printf（Out of memory）; 
} 
 / *初始化新内存* / 
 conductor-> next = 0; 
 conductor-> taskID = taskID; 
 conductor-> priority = priority; 
 
  

来自主要功能：

  int main（）
 {
 struct pqueue * queue; 
 
 createQueue（queue）; 
 add（队列，234093,9332）; 
} 
  

...但我继续保留段落。任何理由为什么这种情况继续发生？

编辑：

pqueue和node的结构如下所示：

  struct node {
 int taskID; 
 int优先级; 
 struct node * next; 
}; 
 
 struct pqueue {
 struct node * root; 
}; 
  

解决方案

在C中，所有东西都是按值传递的。因此，当您调用 createQueue（queue）时，您正在将指针的副本传递给该函数。然后，在函数内部，当您说 queue = malloc（...）时，您将指针的 copy 设置为等于您的新值分配内存 - 保持该指针的 main（）的副本不变。

你想做这样的事情：

  void createQueue（struct pqueue ** queue）
 {
（* queue）= malloc（ ...）; 
} 
 
 int main（void）
 {
 struct pqueue * queue; 
 
 createQueue（& queue）; 
} 
  

这个问题更详细地描述了你的错误。

I'm trying to pass a pointer to a queue into the createQueue function:

void createQueue(struct pqueue *queue){
    queue = malloc( sizeof(struct pqueue) );  
    queue->root = malloc(sizeof(struct node));
    queue->root->next = 0;   
    queue->root->taskID = 12;
    queue->root->priority = 5000;
}

I also try to add to the newly created queue like this:

void add(struct pqueue *queue, int taskID, int priority){
struct node *conductor;
conductor = queue->root;
if ( conductor != 0 ) {
        while ( conductor->next != 0)
        {
                conductor = conductor->next;
        }
}
 conductor->next = malloc( sizeof(struct node) );  
 conductor = conductor->next;
 if ( conductor == 0 )
  {
      printf( "Out of memory" );
  }
  /* initialize the new memory */
  conductor->next = 0;         
  conductor->taskID = taskID;
  conductor->priority = priority;
}

from the main function:

int main()
{
    struct pqueue *queue;       

    createQueue(queue);
    add(queue, 234093, 9332);
}

...but I keep segfaulting. Any reason why this keeps happening?

EDIT:

The structs for pqueue and node are like this:

struct node {
  int taskID;
  int priority;
  struct node *next;
};

struct pqueue{
  struct node *root;
};

解决方案

In C, everything is passed by value. Therefore, when you call createQueue(queue), you are passing a copy of the pointer to the function. Then, inside the function, when you say queue = malloc(...), you are setting that copy of the pointer equal to your newly allocated memory - leaving main()'s copy of that pointer unchanged.

You want to do something like this:

void createQueue(struct pqueue **queue)
{
    (*queue) = malloc( ... );
}

int main(void)
{
    struct pqueue *queue;

    createQueue(&queue);
}

This question has a more detailed description of what's going wrong for you.

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