c - 在处理 strcpy(string, "") 时，字符串未被正确清空和分配

Question

编辑:我确实尝试将行 arr_of_strings[arr_index_count] = first_word; 更改为 strcpy(arr_of_strings[arr_index_count], first_word); 但随后它给出了一个分段打印 Word is: This

后出现错误

编辑 2:我尝试在没有 strtok 的情况下执行此操作，因为我认为这是了解 C 字符串的好方法。

尝试自学 C。决定创建一个函数，它接受一个字符串，并将字符串中的每个单词放入数组中的一个元素中。这是我的代码:

假设 #define MAX_LENGTH = 80

// char *string_one[unknown_size];

// first_word will represent each word in the sentence
char first_word[MAX_LENGTH + 1] = "";

// this is the array I will store each word in
char *arr_of_strings[MAX_LENGTH];

int index_count = 0;
int arr_index_count = 0;

char sentence[] = "This is a sentence.";

for (int i = 0; i<MAX_LENGTH; i++) {
    printf("Dealing with char: %c\n", sentence[i]); 

    if (sentence[i] == '\0') {
        // end of sentence
        break;
    } else if (sentence[i] ==  ' ') {
        // this signifies the end of a word
        printf("Word is: %s\n", first_word);
        arr_of_strings[arr_index_count] = first_word;
        // after putting the word in the string, make the word empty again
        strcpy(first_word, "");
        // verify that it is empty
        printf("First word is now: %s\n", first_word);

        index_count = 0;
        arr_index_count++;
    } else {
        // not the start of a new string... so keep appending the letter to first_word
        printf("Letter to put in first_word is: %c\n", sentence[i]);
        first_word[index_count] = sentence[i];
        index_count++;
    }
}

printf("-----------------\n");
for (int j = 0; j<=arr_index_count; j++) {
    printf("%s\n", arr_of_strings[j]);
}

打印出来的是:

Dealing with char: T
Letter to put in first_word is: T
Dealing with char: h
Letter to put in first_word is: h
Dealing with char: i
Letter to put in first_word is: i
Dealing with char: s
Letter to put in first_word is: s
Dealing with char:  
Word is: This
First word is now: 
Dealing with char: i
Letter to put in first_word is: i
Dealing with char: s
Letter to put in first_word is: s
Dealing with char:  
Word is: isis
First word is now: 
Dealing with char: a
Letter to put in first_word is: a
Dealing with char:  
Word is: asis
First word is now: 
Dealing with char: s
Letter to put in first_word is: s
Dealing with char: e
Letter to put in first_word is: e
Dealing with char: n
Letter to put in first_word is: n
Dealing with char: t
Letter to put in first_word is: t
Dealing with char: e
Letter to put in first_word is: e
Dealing with char: n
Letter to put in first_word is: n
Dealing with char: c
Letter to put in first_word is: c
Dealing with char: e
Letter to put in first_word is: e
Dealing with char: .
Letter to put in first_word is: .
Dealing with char: 
-----------------
sentence.
sentence.
sentence.

如果我们看这里:

First word is now: 
Dealing with char: i
Letter to put in first_word is: i
Dealing with char: s
Letter to put in first_word is: s
Dealing with char:  
Word is: isis

1. 为什么当 word 为空时，我们将 i 和 s 放入其中，word 现在是 isis？ (与 asis 相同)。

2. sentence 这个词怎么打印了 3 次？我的算法显然有缺陷，但如果有的话，单词 sentence 不应该打印 4 次(句子中的每个单词一次:This is a sentence)吗？

另外，我刚学C，所以如果有任何其他改进算法的方法，请告诉我。

Answer 1

arr_of_strings 只是一个 char 指针数组，然后您将所有单词指向数组 first_word。此外，您不使用 C 字符串所需的空终止符。

---

这是一种可能对您有帮助的方法，它使用 strtok :

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

#define N 100
#define LEN 20 // max length of a word

int fill(char matrix[N][LEN], char* data)
{
    // How many words in 'data'?
    int counter = 0;
    char * pch;
    // Splits 'data' to tokens, separated by a whitespace
    pch = strtok (data," ");
    while (pch != NULL)
    {
        // Copy a word to the correct row of 'matrix'
        strcpy(matrix[counter++], pch);
        //printf ("%s\n",pch);
        pch = strtok (NULL, " ");
    }
    return counter;
}

void print(char matrix[N][LEN], int words_no)
{
   for(int i = 0; i < words_no; ++i)
       printf("%s\n", matrix[i]);
}

int main(void)
{
    char data[] = "New to the C programming language";
    // We will store each word of 'data' to a matrix, of 'N' rows and 'LEN' columns
    char matrix[N][LEN] = {0};
    int words_no;
    // 'fill()' populates 'matrix' with 'data' and returns the number of words contained in 'data'.
    words_no = fill(matrix, data);
    print(matrix, words_no);
    return 0;
}

输出:

New
to
the
C
programming
language