create a pointer to an array of structs and pass into function

Question

I have tried accessing each word member from my struct array outside the while loop where I read input but it doesnt print anything.It seems like the array is empty but if I were to put that print statement in my while loop, it works fine.Not sure why this is the case.

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

struct wordArr {
    char words[31];
    int wordCount;
};
 
int main(void) {
    const int ARRSIZE = 300;
    char tmpWord[30] = " ";
    char word[30] = " ";

    // allocate memories for n number of struct wordarr.
    // wordArrptr = (struct wordArr*) malloc(ARRSIZE * sizeof(struct wordArr));
    struct wordArr **wordList = malloc(ARRSIZE * sizeof(struct wordArr *));

    // const char delimiters[10] = " .,";
    for (int i = 0; i < ARRSIZE ; i++) {
        wordList[i] = malloc(sizeof(struct wordArr));
    }

    while (scanf("%s", tmpWord) != EOF) {
        memset(word, ' ', 30);
        int j = 0;
        int i = 0;

        for (int i = 0 ; i < strlen(tmpWord); i++) {
            if (isalpha(tmpWord[i])) {
                word[j] = tolower(tmpWord[i]);
                j++;
            }
        }

        strcpy(wordList[i]->words, word);

        // printf("%s=>\n", wordList[i]->words);
        wordList[i]->wordCount = 1;
        i++;
    }

    for (int i = 0 ; i < ARRSIZE ; i++) {
        printf("%s\n", wordList[i]->words);
    }

    return 0;
}

David Schwartz · Accepted Answer · 2022-03-15 01:10:55Z

1

The %s format specifier for printf is only for C-style strings. C-style strings have a nul (zero) to mark their end. Your code never marks the end of entries in words with a terminator, so you cannot pass words to printf through %s.

Your final for loop goes through every entry -- even ones that you never initialized. That's going to print an awful lot of garbage and possibly even cause a crash as it will also pass things that aren't C-style strings (because they were never initialized at all) to printf through %ss.

answered Mar 15, 2022 at 1:10

David Schwartz

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2 Comments

Ggg Ggff Over a year ago

I have fixed the null terminator issue with my string but why would I need initialise when I have copied the values into the strict in the code block above the final for loop

David Schwartz Over a year ago

You just set wordList[i] equal to the return value from malloc. You never assign wordList[i]->words any value at all, so it doesn't contain a C-style string.

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