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;
}

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;
}

Sorry for wasting your time

What about doing

Code:

*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;
}

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

Code:

this
is
a
random
test

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.