从C中的文件创建动态分配的字符串

Question

我在动态分配树中节点的字符串时遇到了一些问题。我已经在下面包含了我的节点结构以供参考。

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

我应该从文本文件中读取单词，然后将这些单词存储到树中。我可以存储已定义的char数组，例如char string [20]，但不包含应该动态分配的字符串。

我只会发布我正在使用的代码来读取我的文件，并尝试创建动态分配的数组。我已经创建了文件指针并检查它不是NULL。每次我尝试运行该程序时，它都会崩溃，我是否需要尝试逐字读取字符？

//IN MAIN 
node *p, *root ; 
int i; 
int u; 

root = NULL; 
char input[100]; 

while(fscanf(fp, "%s", &input) != EOF) 
{ 
    //Create the node to insert into the tree 
    p = (node *)malloc(sizeof(node)); 
    p->left = p->right = NULL; 

    int p = strlen(input); //get the length of the read string 
    char *temp = (char*) malloc(sizeof(char)*p); 
    //malloc a dynamic string of only the length needed 

    strcpy(local, input); 
    strcpy(p->word,local); 

    insert(&root, p); 
} 

要完全清楚，我只希望关于我的代码逻辑的建议，只希望有人帮我指出了正确的方向。

Answer 1

你被

• 调用很多不确定的行为，传递指针目标对象的类型错误scanf()。即在fscanf(ifp, "%s", &input)，char(*)[100]传递其中char*预计
• 访问使用缓冲的值经由malloc()分配和strcpy(curr->word,local);

未初始化在 strcpy(local, input);

storeing终止空字符时外的范围分配的缓冲区的

您的代码应该是这样的：

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

typedef struct node_t { 
    struct node_t* left, *right; 
    int count; 
    char* word; 
} node; 
void insert(node ** tree, node * item); 

int main(void) { 
    FILE* ifp = stdin; 

    node * curr, * root; 
    int i; 
    int u; 

    root = NULL; 
    char input[100]; 

    /* you should specify the maximum length to read in order to avoid buffer overrun */ 
    while(fscanf(ifp, "%99s", input) != EOF) 
    { 
     //Create the node to insert into the tree 
     curr = malloc(sizeof(node)); 
     if(curr == NULL) /* add error check */ 
     { 
      perror("malloc 1"); 
      return 1; 
     } 
     curr->left = curr->right = NULL; 
     curr->count = 1; 

     int p = strlen(input); //get the length of the read string 
     char *local = malloc(sizeof(char)*(p + 1)); /* make room for terminating null-character */ 
     if (local == NULL) /* add error check again */ 
     { 
      perror("malloc 2"); 
      return 1; 
     } 
     //malloc a dynamic string of only the length needed 

     //To lowercase, so Job and job is considered the same word 
     /* using strlen() in loop condition is not a good idea. 
     * you have already calculated it, so use it. */ 
     for(u = 0; u < p; u++) 
     { 
      /* cast to unsigned char in order to avoid undefined behavior 
      * for passing out-of-range value */ 
      input[u] = tolower((unsigned char)input[u]); 
     } 

     strcpy(local, input); 
     curr->word = local; /* do not use strcpy, just assign */ 

     insert(&root, curr); 
    } 

    /* code to free what is allocated will be here */ 
    return 0; 
} 

//Separate insert function 
void insert(node ** tree, node * item) 
{ 
    if(!(*tree)) 
    { 
     *tree = item; 
     return; 
    } 
     if(strcmp(item->word,(*tree)->word) < 0) 
      insert(&(*tree)->left, item); 
     else if(strcmp(item->word,(*tree)->word) > 0) 
      insert(&(*tree)->right, item); 
     /* note: memory leak may occur if the word read is same as what is previously read */ 
}