CODEWITHSUNDEEP
carrayspointersrealloc
Rich
Rich

Reputation: 71

Pointers and Reallocation in C

I'm fairly new to C; been at it for 3 weeks in a class. I am having a bit of trouble with pointers, and am sure there is probably an easy fix. So basically, this program is supposed to read a word from an input file, store it in an array of pointers with memory allocation, print the word and the normalized form of the word (irrelevant process), and then reallocate the space so that the pointer array will grow as more words are inputted. However, I am having a bit of trouble getting the words to print and the array to reallocate (I currently have it set to a fixed size just to troubleshoot the whole printing aspect). Let me know if there is something wrong with my variable declarations, or if I am just making a stupid mistake please (I am sure it is the probably a combination of the two). Again, I'm very new to C, so I apologize if this is an easy question. 

char * word_regular[100];
char * word_norm[100];

int main (int argc, char * argv[])
{

    if (argc != 2){
        printf("You have not entered a valid number of files.\n");
        exit(1);
    }

    FILE * f_in = fopen(argv[1],"r");
    int i = 0;
    char word[512];
    char norm_word[512];

    while(fscanf(f_in, "%s", word) != EOF) {
        if (is_valid_entry(word)) {
            word_regular[i] = malloc(sizeof(char) * strlen(word) + 1);
            strcpy(word_regular[i],word);
            printf("%s\n",*word_regular[i]);
            word_norm[i] = malloc(sizeof(char) * strlen(norm_word) + 1);
            normalize(word, norm_word);
            strcpy(word_norm[i],norm_word);
            printf("%s\n", *word_norm[i]);
            i++;

Upvotes: 1

Views: 189

Answers (2)

fkl
fkl

Reputation: 5535

Some problems that are with your current code (ignoring the dynamic size need as opposed to fixed since you already said you are using that to debug),

printf("%s\n",*word_regular[i]);

%s takes a char * for printing, so it should be

printf("%s\n",word_regular[i]);

For the second printf, since norm_word itself is a char array,

you should simply use

printf("%s\n", &norm_word[i]);

If you want to print string starting from the ith index.

Update: A quick tip is to pay attention whether you are copying the \0 with strings or not. Because your api calls, such as strlen would go beyond string crashing (or worst silently), unless it is null terminated.

Upvotes: 1

MByD
MByD

Reputation: 137322

  1. The problem with your printf call is that you pass a char (*word_regular[i], *norm_word[i]) instead of char * (word_regular[i], word_norm[i]) when trying to print a string.

  2. If you want to dynamically grow the array, you need to dynamically allocate it in the first place, so instead of declaring arrays of pointers:

    char * word_regular[100];
char * word_norm[100];

    You need to declare pointers to pointers:

    char ** word_regular;
char ** word_norm;

    Allocate an initial buffer for them (in a function, main for example):

    word_regular = malloc(sizeof(char *) * INITIAL_AMOUNT);

    Then reallocate them as needed.

    word_regular = realloc(word_regular, sizeof(char *) * new_amount);

    You will need to keep track of the amount of pointers in the arrays, and free them properly of course...

Upvotes: 0

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