结构体指针初始化错误：为何struct Link * temp = cap;无法输出链表赋值内容？

Hey AndyE, let's figure out why that struct Link * temp = cap; line isn't showing the values you assigned to your linked list. There are a handful of common mistakes that cause this—let's walk through them step by step:

• Your cap pointer isn't actually pointing to the head of your populated list
  It's easy to mess up the initial pointer assignment. For example, if you initialized cap as NULL but forgot to update it when adding the first node, or accidentally overwrote cap later in your code (like pointing it to a middle node or freeing it), then temp will just inherit that broken pointer. No valid node means no values to output.

• You skipped assigning values to your nodes' data fields
  Allocating memory for a node with malloc only gives you raw, uninitialized memory—you have to explicitly set the data values. If your code looks like this:

  struct Link *new_node = malloc(sizeof(struct Link));
  // Oops! No line like new_node->data = 42; here
  new_node->next = cap;
  cap = new_node;
  

  Then even though temp points to cap, the "values" you're trying to print are just garbage memory values.

• You're printing the wrong thing (or using incorrect syntax)
  Double-check how you're outputting the values. If you're printing temp directly, that's just the memory address of the node, not its data. Make sure you're accessing the correct field in your struct. For example, if your struct is defined as:

  struct Link {
      int value;
      struct Link *next;
  };
  

  You need to use printf("%d\n", temp->value); instead of printf("%d\n", temp); or a misnamed field like temp->data.

• Your linked list memory was corrupted or freed prematurely
  If you called free() on cap or any nodes before assigning temp, or had an out-of-bounds write that messed up the list's memory, temp will point to invalid memory. This can lead to garbage output or even program crashes.

Here's a quick working example to compare against your code:

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

struct Link {
    int data;
    struct Link *next;
};

int main() {
    struct Link *cap = NULL;

    // Add first node
    struct Link *first_node = malloc(sizeof(struct Link));
    first_node->data = 15;
    first_node->next = NULL;
    cap = first_node;

    // Add second node
    struct Link *second_node = malloc(sizeof(struct Link));
    second_node->data = 30;
    second_node->next = cap;
    cap = second_node;

    // Traverse and print values
    struct Link *temp = cap;
    while (temp != NULL) {
        printf("Node value: %d\n", temp->data); // Will print 30, then 15
        temp = temp->next;
    }

    // Clean up memory
    temp = cap;
    while (temp != NULL) {
        struct Link *next_node = temp->next;
        free(temp);
        temp = next_node;
    }

    return 0;
}

If you can share a bit more of your code (like how you initialized the list, added nodes, and tried to print the values), I can help pinpoint the exact issue.

内容的提问来源于stack exchange，提问作者AndyE