带有字符串的链接列表

Question

我正在尝试创建一个程序，该程序首先解析多个字符串并将它们添加到链接列表中，然后以打印出每个字符串的出现次数结束。

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#include<stdio.h>\n#include<stdlib.h>\n#include<stdbool.h>\ntypedef struct Node Node;\n\nstruct Node\n{\n    char* word;\n    int count;\n    struct Node *next;\n};\n\nNode *head = NULL;\nNode *curr = NULL;\n\nNode* listAdd(char* word, bool toEnd) {\n    Node* tmp = head;\n    while (tmp) {\n        if (strcmp(tmp, word) == 0) {\n            tmp->count++;\n            return tmp;\n        }\n        tmp = tmp->next;\n    }\n    printf("allocate memory for node");\n    Node *ptr = malloc(sizeof(Node));\n\n    printf("initialize count to 0");\n    ptr->count = 0;\n\n    printf("allocate memory to hold word");\n    ptr->word = malloc(strlen(word) + 1);\n\n    printf("copy the current word");\n    strcpy(ptr->word, word);\n\n    ptr->next = NULL;\n\n    if (toEnd)\n    {\n        curr->next = ptr;\n        curr = ptr;\n    }\n    else\n    {\n        ptr->next = head;\n        head = ptr;\n    }\n    return ptr;\n}\n\nvoid printList()\n{\n    Node *ptr = head;\n    while (ptr)\n    {\n        printf("\\nThe word [%s] has had [%d] occurrences.\\n",ptr->word, ptr->count);\n        ptr = ptr->next;\n    }\n}\n\nchar* readWord()\n{\n    static char buffer[100];\n    scanf("%s", buffer);\n    printf("listAdd() call");\n    listAdd(buffer);\n    return buffer;\n}\n\nint main(void)\n{\n    int i = 0;\n    printf("How many words would you like to type?\\n");\n    scanf("%d", &i);\n    for (i; i != 0; i--)\n    {\n        readWord();\n    }\n    printList();\n}\n

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电流输出：

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How many words would you like to input?\n3\nhi\nbye\nyes\nHow many words would you like to input?\nOccurrences: 12086064\n

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任何帮助将不胜感激 \xe2\x80\x94 我仍然是来自 C# 的 C 新手:(

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Answer 1

您的代码包含一些错误。首先，您将Nodeptr 分配两次：

Node* listAdd(char* word, bool toEnd) {
  // .. 

  Node *ptr = malloc(sizeof(Node));
  return ptr;
}

删除语句前面的最后一个return。

您还需要分配内存来保存每个读取的字。现在，每次调用时都会覆盖缓冲区readWord()。然后你会做类似的事情：

Node* listAdd(char* word, bool toEnd) {
  // allocate memory for node
  Node *ptr = malloc(sizeof(Node));
  // initialize count to 0
  ptr->count = 0;
  // allocate memory to hold word
  ptr->word = malloc(strlen(word) + 1);
  // copy the current word
  strcpy(ptr->word, word);

你的printList()函数需要看起来像这样：

void printList() {
  Node* ptr = head;
  while(ptr) {
    printf("Word: %s %d\n", ptr->word, ptr->count);
    ptr = ptr->next;
  }
}

由于您从不检查输入的单词是否已存在于列表中，所以每个单词将始终被报告为出现 1 次。这可以这样修复：

// check if the word alreay exists in the list and then increment its count by 1
// this code should go at the top (before allocating ptr) in listAdd()
Node* tmp = head;
while(tmp) {
   if(strcmp(tmp->word, word) == 0) {
     tmp->count++;
     return tmp;
   }
   tmp = tmp->next;
}

当然，您还应该在退出应用程序之前释放分配的内存：

void freeList() {
  Node* ptr = head;
  Node* tmp = 0;
  while(ptr) {
    tmp = ptr->next;
    free(ptr->word);
    free(ptr);
    ptr = tmp;
  }