Question

我不知道如何将字符串从inputString复制到newNode->data。

我的结构如下：

typedef struct node {
    char *data;
    struct node *left;
    struct node *right;
} node;

问题函数如下：

node* addToTree(char inputString[]) {
    node *newNode;

    if ((newNode = malloc(sizeof(node*))) == NULL) {
        printf("Error: could not allocate memory");
        exit(-1);
    }

    if ((newNode->data = malloc(strlen(inputString) + 1)) == NULL) {
        printf("Error: could not allocate memory");
        exit(-1);
    }

    /* This line of code doesn't seem to copy anything to newNode->data. 
       This is the way I believe should work, however I don't understand what the 
       problem with it is. I have tried strlcpy and strncpy as well. */
    strcpy(newNode->data, inputString);


    /* The line below here seems to work when I print the value
       within the function, but some of the values are garbage when
       I try to use them later on in the program. */
    newNode->data = inputString;


    newNode->left = NULL;
    newNode->right = NULL;
    printf("Input string: %s\n", inputString);
    printf("New node data: %s\n", newNode->data);

    return newNode;
}

Answer 1

您的sizeof(node*)并不代表您需要的尺寸。

newnode = malloc(sizeof(node*))    // wrong
newnode = malloc(sizeof (node))    // correct
newnode = malloc(sizeof *newNode)  // better

为什么sizeof *newNode更好？

因为它防止了类型更改后在两个处意外忘记更新代码

struct node {
    char *data;
    struct node *next;
    struct node *prev;
};
struct nodeEx {
    char *data;
    size_t len;
    struct nodeEx *next;
    struct nodeEx *prev;
};

struct nodeEx *newnode = malloc(sizeof (struct node)); // wrong
struct nodeEx *newnode = malloc(sizeof *newnode);      // correct

Answer 2

以下行未分配所需的内存量，而是分配了等于指向 node的指针的大小的内存。

if ((newNode = malloc(sizeof(node*))) == NULL)

因此您的strcpy失败，因为没有可复制的内存。

将以上内容更改为：

if ((newNode = malloc(sizeof(node))) == NULL)

执行以下操作后会发生未定义的行为，因为代表inputString的内存可以被覆盖，这就是为什么以后会得到垃圾值的原因。

newNode->data = inputString;

您可以查看此question的最佳答案，以获取更多信息。

Answer 3

newNode->data = inputString;

不正确，它会覆盖之前malloc版的内存。

if ((newNode->data = malloc(strlen(inputString) + 1)) == NULL) {
    printf("Error: could not allocate memory");
    exit(-1);
}
strcpy(newNode->data, inputString);

足以分配内存并将字符串复制到其中。

将字符串复制到结构成员

3 个答案: