Problem with malloc and pointers to pointers

In this function I am trying to malloc an array of pointers, then for each pointer malloc space for a string. It compiles, but segfaults at the highlighted line. What am I doing wrong?

Code:

---

int LoadWordList(char *fname, char **list)
{
        FILE *fp = fopen(fname, "r");
        char ch;
        char string[MAX_LEN];
        int linecount = 0, i, len;

        if(! fp)                       
        {
                printf("Error: Unable to open wordlist file.\n");
                exit(EXIT_FAILURE);
        }
        while((ch = fgetc(fp)) != EOF)
                if(ch == '\n') linecount++;
        rewind(fp);

        *list = (char*)malloc(linecount+1);

        for(i=0; i<linecount; i++)
        {
                fgets(string, MAX_LEN, fp);
                len = strlen(string);
                list[i] = (char*)malloc(len+1);  // Segfaults here
                //strcpy(list[i], string);
                //printf("%s", list[i]);
        }               
        return linecount;
}

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Cheers.

Ok I think I figured it out. This seems to work:

Code:

---

int LoadWordList(char *fname, char **list)
{
        FILE *fp = fopen(fname, "r");
        char ch;
        char string[MAX_LEN];
        int linecount = 0, i, len;

        if(! fp)                       
        {
                printf("Error: Unable to open wordlist file.\n");
                exit(EXIT_FAILURE);
        }
        while((ch = fgetc(fp)) != EOF)
                if(ch == '\n') linecount++;
        rewind(fp);

        list = (char**)malloc(linecount+1);

        for(i=0; i<linecount; i++)
        {
                fgets(string, MAX_LEN, fp);
                len = strlen(string);
                list[i] = (char*)malloc(len+1); 
                strcpy(list[i], string);
                printf("%s", list[i]);
        }               
        return linecount;
}

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Sorry for wasting your time ;)

What about doing

Code:

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*list = (char *)malloc(linecount*sizeof(char *))

---

so that *list is in fact an array of char *, instead of char?

Well, you might need to add another level of indirection to your second parameter... something like

Code:

---

int LoadWordList(char *fname, char ***list)
{
  // ...
  *list = malloc(linecount * sizeof(char *));
 
  // ...
  for (i = 0; i < linecount; i++)
  {
      // ...
      (*list)[i] = malloc((len + 1) * sizeof(char));
  }

  // ...
}

int main()
{
  char **list;
  LoadWordList("someArgument", &list);
  // ...
}

---

By the way, if you use the "figure it out" code you just posted, your second parameter become useless since you are not using the value of it, just putting a result of malloc in it. In fact, i believe what you just posted doesn't work.

Erm, yeah good point. My way worked but crashed when I try and access stuff bak in main. Problem is I can't seem to get your way to work either. It Segfaults on the same line where I malloc space for the strings:

Code:

---

                list[i] = (char*)malloc(len+1);

---

Ok, I tried the way you suggested foxman, but gcc gave errors about incompatible pointer types . I got it to compile by adding another * to the first malloc, but then it segfaulted. If possible I'd really like to avoid the extra indirection as it makes things confusing.

Edit: this is what I had:

Code:

---

int LoadWordList(char *fname, char ***list)
{
        FILE *fp = fopen(fname, "r");
        char ch;
        char string[MAX_LEN];
        int linecount = 0, i, len;

        if(! fp)                       
        {
                printf("Error: Unable to open wordlist file.\n");
                exit(EXIT_FAILURE);
        }
        while((ch = fgetc(fp)) != EOF)
                if(ch == '\n') linecount++;
        rewind(fp);

        **list = (char*)malloc((linecount)*sizeof(char*));

        for(i=0; i<linecount; i++)
        {
                fgets(string, MAX_LEN, fp);
                len = strlen(string);
                (*list)[i] = (char*) malloc(len+1);  // Segfaults here
                //strcpy(list[i], string);
        }               
        return linecount;
}

---

Indeed, i'm not quite sure to understand why it's not working for you because i just tested it and it does work, and got no warnings concerning incompatible pointer types. I use Visual Studio 2005, with the compiling as C code option and warning set to max.

Here is the source code

Code:

---

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define NOM_FICH "test.txt"
#define MAX_LEN 200

int LoadWordList(char *fname, char ***list)
{
        FILE *fp = fopen(fname, "r");
        char ch;
        char string[MAX_LEN];
        int linecount = 0, i, len;

        if(! fp)                       
        {
                printf("Error: Unable to open wordlist file.\n");
                exit(EXIT_FAILURE);
        }
        while((ch = fgetc(fp)) != EOF)
                if(ch == '\n') linecount++;
        rewind(fp);

        *list = malloc(linecount * sizeof(char *));

        for(i=0; i<linecount; i++)
        {
                fgets(string, MAX_LEN, fp);
                len = strlen(string);
                (*list)[i] = malloc((len + 1) * sizeof(char));
                strcpy((*list)[i], string);
        }               
        return linecount;
}

int main()
{
  char **list;
  int i;
  int nbElement;

  nbElement = LoadWordList(NOM_FICH, &list);
  for (i = 0; i < nbElement; i++)
  {
      printf("&#37;s", list[i]);
  }

  return 0;
}

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And here the "test.txt" file i was using

Code:

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this
is
a
random
test

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Ok I see what my problem was. It was that I was still castiing the return value of malloc. Thanks foxman, that works. I guess the extra indirection is needed if i want to save the content of the list without returning the list pointer.