CODEWITHSUNDEEP
carrayscharconcatenation
Alessandro Lorusso
Alessandro Lorusso

Reputation: 357

Adding strings to a char array and separating by \0 in C

I'm trying to write some code that keeps adding words to a character array called sTable separated by \0. The final contents of sTable would look something like:

"word\0int\0paper\0mushroom\0etc\0"

My first thought would be to read the words into a separate character array , tempWord, and concatenate them together, however, how would I be able to add \0 between them and keep sTable ass the final array? I'm not very familiar with C, thank you in advance for the help!

Upvotes: 0

Views: 2075

Answers (1)

ad absurdum
ad absurdum

Reputation: 21318

You can do this by keeping a pointer for the next location in the word array that should receive a word. The function add_word() below takes a pointer to a location in an array of chars and a string. After adding wrd to the location beginning at next, a pointer to the location following the null terminator is returned. The next pointer is initially given the address of the first location in the character array words[]. Keep in mind that there is no error checking here, so the caller is responsible for ensuring that the string will fit in the array.

#include <stdio.h>

#define MAX_SIZE  1000

char * add_word(char *next, const char *wrd);

int main(void)
{
    char words[MAX_SIZE];
    char *next = words;

    next = add_word(next, "word");
    next = add_word(next, "int");
    next = add_word(next, "mushroom");
    next = add_word(next, "etc");

    for (char *ptr = words; ptr < next; ptr++) {
        if (*ptr == '\0') {
            printf("\\0");
        } else {
            putchar(*ptr);
        }
    }

    putchar('\n');

    return 0;
}

char * add_word(char *next, const char *wrd)
{
    while (*wrd != '\0') {
        *next++ = *wrd++;
    }
    *next++ = '\0';

    return next;
}

Program output:

word\0int\0mushroom\0etc\0

Here is a version of the above program that has been modified so that the add_word() function takes an index for the starting location of the word being added, and returns and index for the next word. An array, word_indices[] has also been added to save the starting indices for each word added to words[].

#include <stdio.h>

#define MAX_SIZE  1000

size_t add_word(char *tokens, size_t next, const char *wrd);

int main(void)
{
    char words[MAX_SIZE];
    size_t word_indices[MAX_SIZE] = { 0 };
    size_t  next = 0, count = 0;

    char *input[4] = { "word", "int", "mushroom", "etc" };

    for (size_t i = 0; i < 4; i++) {
        next = add_word(words, next, input[i]);
        word_indices[++count] = next;
    }

    /* Show characters in words[] */
    for (size_t i = 0; i < next; i++) {
        if (words[i] == '\0') {
            printf("\\0");
        } else {
            putchar(words[i]);
        }
    }
    putchar('\n');

    /* Print words in words[] */
    for (size_t i = 0; i < count; i++) {
        puts(&words[word_indices[i]]);
    }

    return 0;
}

size_t add_word(char *tokens, size_t next, const char *wrd)
{
    while (*wrd != '\0') {
        tokens[next++] = *wrd++;
    }
    tokens[next++] = '\0';

    return next;
}

Program output:

word\0int\0mushroom\0etc\0
word
int
mushroom
etc

Upvotes: 2

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