[Resolved] Dynamic Array of Struct in C?

[The Hobo]

If I had this:

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

//...

PersonalInfo *userInfos;

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

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.

[twanvl]

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.

[hYph3n]

to access the pointer with in a struct use

struct -> pointerOfStruct;

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

to access simple members

struct.memberName;

//in your case

userInfos.age;

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

[The Hobo]

How would I allocate the char pointer in the struct?

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

Crashes when I run it.

[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:

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

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

[The Hobo]

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:

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

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

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...

[The Hobo]

Okay, still not working:

#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();
    }
}

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)?

[sunburnt]

I made a couple changes, give this a try:

#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();
    }
}

[The Hobo]

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?:

#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);
}

[The Hobo]

Figured it out:

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

Thanks for the help, everyone.