Question

我试过寻找答案但找不到足够具体的东西。在以下代码中......

typedef struct node
{
    bool is_word;
    struct node *children[27];
}Node;

Node root;
Node *rootptr = &root;

for(int i = 0; i < 27; i++)
{
      rootptr->children[i] = NULL;
}
rootptr -> is_word = false;

我收到以下编译错误，我不太明白。

~/workspace/pset5/speller/ $ make
clang -ggdb3 -O0 -Qunused-arguments -std=c11 -Wall -Werror   -c -o 
speller.o speller.c
clang -ggdb3 -O0 -Qunused-arguments -std=c11 -Wall -Werror   -c -o 
dictionary.o dictionary.c
dictionary.c:22:5: error: expected identifier or '('
    for(int i = 0; i < 27; i++)
    ^
dictionary.c:26:5: error: unknown type name 'rootptr'
    rootptr -> is_word = false;
    ^
dictionary.c:26:13: error: expected identifier or '('
    rootptr -> is_word = false;
        ^
3 errors generated.
make: *** [dictionary.o] Error 1

这是我的speller.c的完整代码（我知道它有其他逻辑错误，但我只是想先了解一下。

/**
* Implements a dictionary's functionality.
*/

#include <stdbool.h>
#include "dictionary.h"
#include <string.h>
#include <stdlib.h>
#include <stdio.h>



typedef struct node
{
    bool is_word;
    struct node *children[27];
}Node;

Node root;
Node *rootptr = &root;

for(int i = 0; i < 27; i++)
{
      rootptr->children[i] = NULL;
}
rootptr -> is_word = false;

unsigned int counter = 0;

/**
* Returns true if word is in dictionary else false.
*/
bool check(const char *word)
{
    Node *travptr = rootptr;
    int letter = 0;
    for(int i = 0, n = strlen(word);  i < n; i++)
    {
        letter = word[i];
        letter = letter - 96;

        if(travptr -> children[letter] != NULL)
        {
            if(i < n-1)
            {
                travptr = travptr -> children[letter];
            }
            else return travptr -> is_word;
        }
        else return false;
    }
    return false;
}

/**
* Loads dictionary into memory. Returns true if successful else false.
*/
bool load(const char *dictionary)
{
    char *word = malloc(LENGTH +1);
    int letter = 0;
    Node *travptr = NULL;

    FILE *dict = fopen(dictionary, "r");
    if(dict == NULL)
    {
        return false;
    }

    while(fscanf(dict, "%s", word) != EOF)
    {
        travptr = rootptr;

        for(int i = 0, n = strlen(word);  i < n; i++)
        {
            letter = word[i];
            letter = letter - 96;

            if(travptr -> children[letter] == NULL)
            {
                Node *newptr = malloc(sizeof(Node));
                if(newptr == NULL)
                {
                    unload();
                    return false;
                }
                for(int i = 0; i < 27; i++)
                {
                    newptr -> children[i] = NULL;
                }
                newptr -> is_word = false;
                if(i == n-1)
                    newptr -> is_word = true;

                travptr = newptr    ;

            }
            else travptr = travptr -> children[letter];
        }
        counter++;
    }
    fclose(dict);
    return true;

}   

/**
* Returns number of words in dictionary if loaded else 0 if not yet loaded.
*/
unsigned int size(void)
{
    // TODO
    return counter;
}

/**
* Unloads dictionary from memory. Returns true if successful else false.
*/
bool unload(void)
{
    Node *travptr = rootptr;
    for(int i = 0; i < 27; i++)
    {
        if(travptr -> children[i] != NULL)
        {
            travptr = travptr -> children[i];
            unload();
        }
        else free(travptr);
    }
    return true;

}

Answer 1

您不能在文件范围内放置语句。所以整个块都是非法的：

for(int i = 0; i < 27; i++)
{
      rootptr->children[i] = NULL;
}
rootptr -> is_word = false;

您可以将其移动到您将在main的开头调用的函数：

void init_root(void) 
{
    for(int i = 0; i < 27; i++)
    {
          rootptr->children[i] = NULL;
    }
    rootptr -> is_word = false;
}

int main(void) 
{
  init_root();
}

或者使用稍微繁琐的路线并使用适当的初始化程序初始化root：

Node root = {
  .is_word = false,
  .children[0] = NULL,
  .children[1] = NULL,
  // ...
  .children[26] = NULL,
};

Answer 2

for循环或rootptr -> is_word = false;之类的内容是语句，必须出现在函数内。

不明白cs50 speller编译错误

2 个答案: