将字符串转换为 C 中的字符串数组

Question

I'm trying to divide a string of alphabetically sorted words char *str = "a/apple/arm/basket/bread/car/camp/element/..." into an array of strings alphabetically like so:

arr[0] = "a/apple/arm"
arr[1] = "basket/bread"
arr[2] = "car/camp"
arr[3] = ""
arr[4] = "element"
...

I'm not very skilled in C, so my approach was going to be to declare:

char arr[26][100]; 
char curr_letter = "a";

and then iterate over each char in the string looking for "/" follow by char,= curr_letter. then strcpy that substring to the correct location.

I'm not sure if my approach is very good, let alone how to implement it properly. Any help would be greatly appreciated!

Answer 1

So we basically loop through the string, and check if we found the "split character' and we also check that we didn't find the 'curr_letter' as the next character.

We keep track of the consumed length, the current length (used for memcpy later to copy the current string to the array).

When we find a position where we can add the current string to the array, we allocate space and copy the string to it as the next element in the array. We also add the current_length to consumed, and the current_length is reset.

We use due_to_end to find out if we have a / in the current string, and remove it accordingly.

Try:

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

int main() {
        char *str = "a/apple/arm/basket/bread/car/camp/element/...";
        char split_char = '/';
        char nosplit_char = 'a';

        char **array = NULL;
        int num_elts = 0;

        // read all the characters one by one, and add to array if 
        // your condition is met, or if the string ends
        int current_length = 0; // holds the current length of the element to be added
        int consumed = 0; // holds how much we already added to the array
        for (int i = 0; i < strlen(str); i++) { // loop through string
                current_length++; // increment first
                int due_to_end = 0;
                if ( ( str[i] == split_char // check if split character found
                    && ( i != (strlen(str) - 1) // check if its not the end of the string, so when we check for the next character, we don't overflow
                    && str[i + 1] != nosplit_char ) ) // check if the next char is not the curr_letter(nosplit_char)
                   || (i == strlen(str) - 1 && (due_to_end = 1))) { // **OR**, check if end of string
                        array = realloc(array, (num_elts + 1) * sizeof(char *)); // allocate space in the array
                        array[num_elts] = calloc(current_length + 1, sizeof(char)); // allocate space for the string
                        memcpy(array[num_elts++], str + consumed, (due_to_end == 0 ? current_length - 1 : current_length)); // copy the string to the current array offset's allocated memory, and remove 1 character (slash) if this is not the end of the string

                        consumed += current_length; // add what we consumed right now
                        current_length = 0; // reset current_length
                }
        }

        for (int i = 0; i < num_elts; i++) { // loop through all the elements for overview
                printf("%s\n", array[i]);
        }

}

Answer 2

Yes, the approach that you specify in your question seems good, in principle. However, I see the following problem:

Using strcpy will require a null-terminated source string. This means if you want to use strcpy , you will have to overwrite the / with a null character. If you don't want to have to modify the source string by writing null characters into it, then an alternative would be to use the function memcpy instead of strcpy . That way, you can specify the exact number of characters to copy and you don't require the source string to have a null terminating character. However, this also means that you will somehow have to count the number of characters to copy.

On the other hand, instead of using strcpy or memcpy , you could simply copy one character at a time from str into arr[0] , until you encounter the next letter, and then copy one character at a time from str into arr[1] , and so on. That solution may be simpler.

In accordance with the community guidelines for homework questions , I will not provide a full solution to your problem at this time.