Thread: Reading a txt file into an array: unexpected segfault

Hi to all!

I have this function that, provided with a target array of strings and a file name, reads it line by line and stores the lines into the given array

Code:

void file_to_array(char **target_lines, char *file_name)
{
	FILE *f;
	char line[LINE_SIZE];
	int num_righe = 0;
	
	f = fopen(file_name, "r");
	/* crea il file se non lo trova */
	if(f == NULL) {
		f = fopen(file_name, "w");
	}
	
	while(fgets(line, LINE_SIZE, f)) {		
		num_righe++;
		target_lines = (char**)realloc(target_lines, (sizeof(char*)*num_righe));
		target_lines[num_righe-1] = strdup(line);
	}

	fclose(f);
}

Calling it like follows it gives me a Segmentation fault in the line where I try to print the second item.

Code:

char **lines = NULL;
file_to_array(lines, "spese.dat");
printf("%s", lines[0]);

The file is correct and outputting like by line within the function ( printf("%s", target_lines[num_righe-1]) ) gives the correct lines.

Any help?
Thanks in advance

Changes made by the called function to lines do NOT make it back to the caller.

Try something like
lines = file_to_array ( lines, "filename" );

And put
return lines;
at the end of the function.

> f = fopen(file_name, "w");
Erm, you're reading from the file, so this won't work anyway.

Oh, and there's no need to cast the result of malloc functions in a C program, if you've done the right thing of including stdlib.h.
See the FAQ

Originally Posted by pistacchio

Oh, this worked, thanks! And of course the function declaration now reads like:

char** file_to_array(char **target_lines, char *file_name)

Out of curiosity, as I'm learning C right now: how can I do the same without a return value but passing a reference to the array (that is what I was trying to do)?
Thanks again

Add a level of indirection:

Code:

void file_to_array(char ***target_lines, const char *filename)
...
file_to_array(&lines, "my file");

You'll have to deal with the extra level of indirection in the function, of course. (Get pointers down - once you do, this sort of thing should be obvious.) In practice, it'll be easier to do what Salem suggested and return a pointer. (It'll make your code in the function much clearer as well.)