Need help with program allocating memory

**jaspar** · 03-26-2017

For some reason the program crashes at the GetFiles function.Anyone willing to help?Thanks

Code:

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


void ReadDirectory(char **maindir);
void GetFiles(char *directory,char ***filenames,int *number);


int main()
{
    int number,i;
    char *maindir = NULL,**mainfilenames = NULL;


    printf("Give the directory where the movies are: ");
    ReadDirectory(&maindir);


    GetFiles(maindir,&mainfilenames,&number);


    for(i=0;i<number;i++)
    {
        printf("%s\n",mainfilenames[i]);
    }


    system("PAUSE");
    return 0;
}


void ReadDirectory(char **maindir)
{
    int c,size = 0;
    char *temp = NULL;


    *maindir = malloc((size+1));
    (*maindir)[size] = '\0';


    size++;


    while((c = getchar()) != EOF && c != '\n')
    {
        temp = realloc(*maindir,size+1);


        if(temp)
        {
            *maindir = temp;
            (*maindir)[size-1] = c;
            (*maindir)[size] = '\0';


            size++;
        }
        else
        {
            printf("Error (A) reallocating memory.\n");
            exit(1);
        }
    }


    temp = NULL;
    free(temp);
}


void GetFiles(char *directory,char ***filenames,int *number)
{
    struct dirent *dent;
    DIR *dir;
    int size;
    char **temp;


    if((dir = opendir(directory)) == NULL)
    {
        printf("Can't open directory %s!\n",dir);
        exit(2);
    }


    size = 0;
    *number = 0;


    *filenames = malloc(*number+1);
    (*filenames)[*number] = malloc(size+1);


    (*filenames)[*number][size] = '\0';


    while ((dent = readdir(dir)) != NULL)
    {
        if (!strcmp(dent->d_name,".") || !strcmp(dent->d_name,".."))
        {
            continue;
        }


        temp = realloc(*filenames,*number+1);


        if(temp)
        {
            *filenames = temp;


            while(dent->d_name[size] != '\0')
            {
                size++;
                temp[*number] = realloc((*filenames)[*number],size+1);


                if(temp[*number])
                {
                    (*filenames)[*number] = temp[*number];
                    (*filenames)[*number][size-1] = dent->d_name[size-1];
                    (*filenames)[*number][size] = '\0';
                }
                else
                {
                    printf("Error (C) reallocating memory.\n");
                    exit(1);
                }
            }
        }
        else
        {
            printf("Error (B) reallocating memory.\n");
            exit(1);
        }


        (*number)++;
    }


    closedir(dir);
}

**laserlight** · 03-26-2017

Instead of trying to deal with more than two levels of indirection, I suggest that you make use of some abstraction by declaring structs. For example, you could start with:

Code:

struct Movie
{
    char *filename;
    /* movie name? etc */
};

struct MovieDirectory
{
    char *filepath;
    struct Movie *movies;
    size_t movie_count;
};

This way, you can then declare:

Code:

void ReadDirectoryName(struct MovieDirectory *maindir);

void ReadDirectoryContent(struct MovieDirectory *maindir);

Note that file and path names usually have some known maximum length, and while path names might be long, the individual file name typically would be limited to say, 255 characters, so instead of using dynamic memory allocation, you could simplify with something like:

Code:

#define FILENAME_MAXLEN 255

struct Movie
{
    char filename[FILENAME_MAXLEN + 1];
    /* movie name? etc */
};

and then only use dynamic memory allocation for the dynamic array of movies. Since you observed the problem in GetFiles, this could well help avoid/fix the problem when you implement ReadDirectoryContent.

By the way, instead of reallocating character by character read as in your ReadDirectory function, it would likely be more efficient to use fgets in a loop to read a block of characters until EOF or a newline is encountered, i.e., expand the memory allocated, read into the start of the newly allocated area, then check the newly read area for a newline and check if fgets returned a null pointer. Also, it pointless to free(temp) right after setting temp to NULL.

**jaspar** · 03-26-2017

Thank you for your tips , some are helpfull to me since i didnt know if what i was doing had any point (temp = NULL , free(temp)).However i dont want to change my thinking of allocating memmory for more than a character , i want to keep it at that one char at a time (read it,allocate memory for it(realloc),store it untill the string has ended then allocate memory for another string and so on...)

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