[Resolved] Dynamic Array of Struct in C?

If I had this:

Code:

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typedef struct {
    char *name;
    int age;
} PersonalInfo;

//...

PersonalInfo *userInfos;

userInfos = (PersonalInfo *) calloc(1, sizeof(PersonalInfo));

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How would I access the members of userInfos? I've tried many combinations with . and -> but nothing seems to work. Plenty of errors and crashes.

You can use it as an array:
userInfos[0].name = ...;
Or as a pointer:
userInfos->name = ...;
Both should work. Also, don't forget to free() your memory.

to access the pointer with in a struct use

Code:

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struct -> pointerOfStruct;

userInfos -> name;
// in your case it would be

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to access simple members

Code:

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struct.memberName;

//in your case

userInfos.age;

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[P.S]: please mark the post as resloved if you have your problem asnwered

How would I allocate the char pointer in the struct?

Code:

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userInfos[0].name = (char *) malloc ...
strcpy(userInfos[0].name, nameVar);

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Crashes when I run it.

are you sure the array you allocate is large enough? If you use strlen to determine the size you must add 1, because the string also stores a '\0' which is not counted by strlen:

Code:

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char* mystring = malloc(strlen(input) + 1);
strcpy(input, mystring);

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Also: Do you have to use C? C++ is much easier, especially for strings and arrays.

Quote:

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Originally Posted by twanvl

are you sure the array you allocate is large enough? If you use strlen to determine the size you must add 1, because the string also stores a '\0' which is not counted by strlen:

Code:

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char* mystring = malloc(strlen(input) + 1);
strcpy(input, mystring);

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Also: Do you have to use C? C++ is much easier, especially for strings and arrays.

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I forgot to add 1, doh. And the class I'm doing this for is a C class...so...yeah, sadly. Don't get me started on my opinions on how the uni runs classes...

Okay, still not working:

Code:

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#include <stdio.h>

const int INITIAL_SIZE = 10;

typedef struct {
        char *word;
        int count;
} WordBank;

main() {
        // define local variables:
        WordBank *words;
    char *word;
        int c, currentWord = 0;

        words = (WordBank *) calloc (INITIAL_SIZE, sizeof (WordBank));
        word = (char *) calloc (25, sizeof (char));

    // get input:
    c = getchar();
    while (c != EOF) {
        // if the character is a space, replace it with \n
        if (isspace(c) || c == '\0') {
                words[currentWord].word = (char *) calloc (strlen(word) + 1, * sizeof(char));
                        strcpy(words[currentWord], word);

          // increment the word counter:
            currentWord++;

                        strcpy(word, "\0");
        // if the character is punctuation, replace it with null
                } else if (ispunct(c)) {
            c = '\0';
                } else {
                        //word = word + c;
                        strcat(word, &c);
                }

        // grab the next character:
        c = getchar();
    }
}

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The code is supposed to copy the input character by character, and each time a full word is found, it adds it to the array.

With the standard example above (PersonalInfo), it works fine, but not in my real code (above)?

I made a couple changes, give this a try:

Code:

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#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
const int INITIAL_SIZE = 10;

typedef struct {
        char *word;
        int count;
} WordBank;

main() {
        // define local variables:
        WordBank *words;
    char *word;
        int c, currentWord = 0;

        words = (WordBank *) calloc (INITIAL_SIZE, sizeof (WordBank));
        word = (char *) calloc (25, sizeof (char));

    // get input:
    c = getchar();
    while (c != EOF) {
        // if the character is a space, replace it with \n
        if (isspace(c) || c == '\0') {
                words[currentWord].word = (char *) calloc(strlen(word) + 1, sizeof(char));
                        strcpy(words[currentWord].word, word);

          // increment the word counter:
            currentWord++;

                        strcpy(word, "\0");
        // if the character is punctuation, replace it with null
                } else if (ispunct(c)) {
            c = '\0';
                } else {
                        //word = word + c;
                        strcat(word, (char*)&c);
                }

        // grab the next character:
        c = getchar();
    }
}

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Awesome, thanks. I don't know how that * got before sizeof(char). One more problem before I call this resolved:

I'm supposed to let the size of the array grow after it reaches INITIAL_SIZE, but I'm screwing up the reallocation somehow. Any ideas?:

Code:

---

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

const int INITIAL_SIZE = 5;

typedef struct {
        char *word;
        int count;
} WordBank;

main() {
        // define local variables:
        WordBank *words, *tmp;
    char *word;
        int c, currentWord = 0;
    int i, index;

        words = (WordBank *) calloc (INITIAL_SIZE, sizeof (WordBank));
        word = (char *) calloc (25, sizeof (char));

    // get input:
    c = getchar();
    while (c != EOF) {
        // if the character is a space, replace it with \n
        if (isspace(c) || c == '\0') {
            if (currentWord > (INITIAL_SIZE - 1)) {
                if ((tmp = realloc(words, sizeof(WordBank) * (currentWord))) == NULL) {
                    fprintf(stderr, "Reallocation failed.");
                }

                words = tmp;
                free(tmp);
            }

            words[currentWord].word = (char *) calloc(strlen(word) + 1, sizeof(char));
           
            strcpy(words[currentWord].word, word);
            words[currentWord].count = 1;

            // increment the word counter:
            currentWord++;

            strcpy(word, "\0");
        // if the character is punctuation, replace it with null
                } else if (ispunct(c)) {
            c = '\0';
                } else {
                        //word = word + c;
                        strcat(word, (char*)&c);
                }

        // grab the next character:
        c = getchar();
    }

    for (i = 0; i < currentWord; i++) {
        printf("%s\n", words[i].word);
    }

    free(words);
}

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Figured it out:

Code:

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if ((tmp = realloc(words, sizeof(WordBank) * (currentWord + 1))) == NULL) {

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Thanks for the help, everyone.