指向無法訪問二維數組值的結構的指針

Question

我目前正在編寫一個充當電路的程序。 我有一個門結構，它采用二維字符數組來保存變量名，但是當我嘗試訪問存儲在 while 循環之外的數組中的這些變量名時，內容為空。

typedef struct Gate
{
    kind_t kind;
    int size;     // size of DECODER and MULTIPLEXER
    char **params; // length determined by kind and size (CHANGED FROM INT TO CHAR)
                  // includes inputs and outputs, indicated by variable numbers
} Gate;

typedef struct Node
{
    Gate *data;
    struct Node *next;
} Node;

// Linked list of gates & attributes
    while (fscanf(fp, "%16s", str) != EOF)
    {
        if (strcmp(str, "AND") == 0)
        {
            head = makeGate(fp, head, AND);
            length++;
        }
        else if (strcmp(str, "OR") == 0)
        {
            head = makeGate(fp, head, OR);
            length++;
        }
        else if (strcmp(str, "NAND") == 0)
        {
            head = makeGate(fp, head, NAND);
            length++;
        }
        else if (strcmp(str, "NOR") == 0)
        {
            head = makeGate(fp, head, NOR);
            length++;
        }
        else if (strcmp(str, "XOR") == 0)
        {
            head = makeGate(fp, head, XOR);
            length++;
        }
        else if (strcmp(str, "NOT") == 0)
        {
            //head = makeGate(fp, head, NOT);
            //length++;
        }
        else if (strcmp(str, "PASS") == 0)
        {
            //head = makeGate(fp, head, PASS);
            //length++;
        }
        else if (strcmp(str, "DECODER") == 0)
        {
            //
        }
        else if (strcmp(str, "MULTIPLEXER") == 0)
        {
            //
        }
        printf("%s\n", head->data->params[2]);
    }

    // plugs in values to circuit
    for (int i = 0; i < 3; i++)
    {
        printf("Stored string: %s\n", head->data->params[i]);
    }

`

Node *makeGate(FILE *fp, Node *head, kind_t inGate)
{
    char str[17];
    Node *new_node = (Node *)malloc(sizeof(Node)); // Node of linkedlist that contains gate structure
    new_node->data = (Gate *)malloc(sizeof(Gate)); // Gate structure that keeps information about a gate
    new_node->next = head;

    new_node->data->kind = inGate;
    new_node->data->size = 3;
    new_node->data->params = malloc(3 * sizeof(char*));
    for (int i = 0; i < 3; i++)
    {
        new_node->data->params[i] = malloc(17 * sizeof(char));
    }

    fscanf(fp, "%16s", str);
    new_node->data->params[0] = str;
    fscanf(fp, "%16s", str);
    new_node->data->params[1] = str;
    fscanf(fp, "%16s", str);
    new_node->data->params[2] = str;
    return new_node;
}

` while 循環內的 printf 語句工作得很好，純粹是為了測試，但是打印數組每個值的 for 循環是不同的，什么也不打印。

我嘗試多次修復此問題但無濟於事，我最初發現此問題是因為我注意到我有 memory 泄漏，當我釋放 memory 泄漏應該在的位置時，它拋出我正在釋放一個未分配的地址。

我唯一的想法是我不知何故丟失/跳過了一個節點，但我沒有想法

Answer 1

以下不會將數據從str復制到struct中（您需要strcpy ）：

new_node->data->params[0] = str;

它所做的是將str的地址復制到每個元素中。 它們都指向相同的緩沖區/字符串。 並且，當 function 返回時， str從 scope 中消失。

您可以[並且應該] 直接掃描到結構中。

所以，改變：

fscanf(fp, "%16s", str);
new_node->data->params[0] = str;

fscanf(fp, "%16s", str);
new_node->data->params[1] = str;

fscanf(fp, "%16s", str);
new_node->data->params[2] = str;

進入：

fscanf(fp,"%16s",new_node->data->params[0]);
fscanf(fp,"%16s",new_node->data->params[1]);
fscanf(fp,"%16s",new_node->data->params[2]);