CODEWITHSUNDEEP
carrayspointersfree
Maillful
Maillful

Reputation: 77

free() an array of char**

I have this :

struct Library {
    char letter;
    int capacity;
    int size;
    char** words;
};
typedef struct Library Lib;

Initialize the array of Library:

void InitLibrary(Program* startup) {
    char alphabet[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
    startup->dictionary = malloc(sizeof(Lib) * 26);
    int i;
    for (i = 0; i < 26; i++) {
        startup->dictionary[i].letter = alphabet[i];
        startup->dictionary[i].capacity = INIT_CAPACITY;
        startup->dictionary[i].size = 0;
        startup->dictionary[i].words = malloc(sizeof(char*) * startup->dictionary[i].capacity);
    }
}

Here i populate the array words :

void FillDicoFromFile(Program* startup){
    while((!feof(startup->f) && !ferror(startup->f))){
        char* word = malloc(sizeof(char) * 30);
        fscanf(startup->f, "%s", word);
        ToLowerCase(word);
        int indexLib = word[0] - 97;
        int sizeLib = startup->dictionary[indexLib].size;
        startup->dictionary[indexLib].words[sizeLib] = word;
        startup->dictionary[indexLib].size++;
    }
    CountTotalWords(startup);
    rewind(startup->f);
}

and a function like this :

void CleanDico(Program* startup){
    int i = 0;
    for(; i < startup->dictionary[i].size; i++){
        int j = 0;
        for(; j < startup->dictionary[i].size; i++){
            free(startup->dictionary[i].words[j]);
            startup->dictionary[i].words[j] = NULL;
        }
        startup->dictionary[i].size = 0;
    }
    startup->totalWords = 0;
}

I got the size of my array on my struct to get the limit of my array, and freed all used cells, but each time I call CleanDico, the code crashes. Any suggestions?

I've already asked a question on a problem with a char array. Now I want to free() the array. I've read plenty of posts here and there and tested a lot of solutions but none helped me to resolve my problem.

I get a SEGMENTATION_FAULT on CleanDico, and I don't have any other informations about the error. Debug mod on Code::Blocks are poor with error messages.

Upvotes: 1

Views: 230

Answers (3)

cokceken
cokceken

Reputation: 2076

Your inner for loop also increments i variable. So it goes out of index.

EDIT: outer loop should run for 26 times since you have 26 letter.

for(; i < 26; i++){
    int j = 0;
    for(; j < startup->dictionary[i].size; j++){
        free(startup->dictionary[i].words[j]);
        startup->dictionary[i].words[j] = NULL;
    }
    startup->dictionary[i].size = 0;
}

Upvotes: 1

John Zwinck
John Zwinck

Reputation: 249592

Every malloc(), calloc(), or realloc() must be matched with a corresponding free() (or realloc()).

You have this:

startup->dictionary[i].words = malloc(sizeof(char*) * N);

Which gives you an array of pointers, uninitialized (they contain garbage).

Later you have this:

free(startup->dictionary[i].words[j]);

Which deallocates a pointer you never initialized. And fails to deallocate what you allocated.

As an aside, you may wish to consider a different data structure: allocate one huge array of char which contains all words, plus one array of char* which contains one pointer to each word. This way you always have exactly two allocations and deallocations (unless you don't know the maximum size of all your words, in which case you might need to realloc() occasionally).

Upvotes: 2

user3794667384
user3794667384

Reputation: 437

I think on your second for you meant to do

for(; j < startup->dictionary[j].size; j++){

instead of 

for(; i < startup->dictionary[i].size; i++){

Upvotes: 4

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