Question

I am building an array and I want it to be a fixed size so that as I read in a file it only stores the last 10 commands. The file seems to read in correctly and it looks right when I print it but for some reason my memory is not getting freed.
MAX is set to 1000
and historySize is read earlier from the user. I ran valgrind on my code and when the calls to these functions are commented out I do not have any leaks.

I have a char ** history under my #includes

Here is my code

void setupHistoryFile()
{
    char string[MAX];
    FILE *fp;
    int len;
    int pos = 0;
    fp = fopen(".ush_history","r");
    if(fp == NULL)
    {
        //create the file
        fp = fopen(".ush_history","w");
    }
    else
    {
        history = (char**)malloc(historySize * sizeof(char*));//setup history file
        fgets(string,MAX,fp);
        len = strlen(string);
        if(string[len-1]=='\n')
            string[len-1]='\0';
        while(!feof(fp))
        {
            if(history[pos] != NULL)
            {
                free(history[pos]);
                history[pos]=NULL;
            }
            history[pos] = (char*)malloc((strlen(string)+1) * sizeof(char));
            //printf("Should be copying %s\n",string);          
            strcpy(history[pos], string);           
            pos++;
            pos = pos % historySize;
            fgets(string,MAX,fp);
            len = strlen(string);
            if(string[len-1]=='\n')
                string[len-1]='\0';
        }
    }
    fclose(fp);
}

I do have a function that cleans the history and it looks like this

void cleanHistory()
{
    int i;
    if(history != NULL)
    {
        for(i=0;i<historySize;i++)
        {
            free(history[i]);
            history[i] = NULL;
        }
        free(history);
        history = NULL;
    }
}

Answer 1

When you allocate memory with malloc, the chunk of memory allocated is not initialized. That means that if you do something like history[pos] != NULL might actually be true even if you haven’t put anything there.

To be certain that the allocated memory is initialized, either use calloc or memset.

Edit
To be more specific, this part of your code will behave badly:

if(history[pos] != NULL)
{
    free(history[pos]);
    history[pos]=NULL;
}

If you are not lucky, history[pos] will contain some old data, which means you will try to free something you have not allocated.

As a small side-note, you should be looping while fgets doesn’t return NULL. As it is now you don’t check for errors from fgets. Something like this:

while (fgets(...) != NULL)

Then you don’t need the double calls to fgets, and you will stop looping on both error and end of file.