Thread: I can't tell what is wrong with this code ARRR!

Dunno, without you post your latest code.

that check after the while loop is wrong.
you don't check if the '\0' still fits into the buffer.
Kurt
EDIT: I would return an empty string ( buffer[0]=0; ) in case nothing was input. This way the calling function would not have to check the returnvalue for NULL. ( just like the c++ getline ).

Code:

char *get_line(FILE *file) 
{
	FILE *fp = file;
	
	char *buffer;
	int ch,  i=0;
	unsigned int buffer_size = BUFFER_SIZE, new_buffer_size;

	assert(buffer_size > 0);

	buffer = (char *) safe_malloc (buffer_size * sizeof (char));
	
	while ((ch = getc(fp)) != EOF )
	{
		
		
		if (buffer_size == i) 
		{
			new_buffer_size = buffer_size * 2;
			assert(new_buffer_size >= buffer_size);
			buffer = (char *) safe_realloc (buffer, new_buffer_size * sizeof (char));
			buffer_size = new_buffer_size;
		}
		
                            if (ch == '\n')			 
		break;
			
                            buffer[i] = ch;
		i++;
	}
	if (i > 0)
	{
		buffer [i] = '\0';
		return buffer;
	}
	else
	{
		free(buffer);
		return NULL;
	}
}

The function needs to return NULL if the index file is empty so I dont know if returning an empty string would work.

The specs for this function are:

"get_line reads a single line of text from its argument file pointer. If the EOF is encountered
immediately without reading any characters from the file, the NULL pointer should be
returned. Otherwise a pointer to a dynamically allocated string should be returned. The
string must be large enough to fit an entire line of input. Lines are ended by the newline
character, or when the EOF is encountered. Ending newline characters should be read in by
the function, but they should NOT be stored in the string which is returned. For example,
if the file contains these characters:
123\n456\n78
The last character in the file is 8, and any attempt to read input after that character will
result in EOF. The first call to get_line on the file will return a string containing these
characters:
123\0
6
The second call to get_line on the file will return a string containing these characters:
456\0
The third call to get_line on the file will return a string containing these characters:
78\0 "

The '\n' is taken care of with regard to allocating the correct buffer_size to the string for storage of the sentinal now that it is included in the body.

My problem is with the EOF, how do I make sure there is space for it if the loop terminates at the EOF and doesnt allocate space for a final NULL, when the case is that EOF is found at the end of a string and buffer_size is unable to be changed?

I hope I make sense....

> It seems my code from the previous post is working!
So you fixed this ?
> how do I make sure there is space for it if the loop terminates at the EOF and doesnt allocate space for a final NULL

If you make sure the string is always \0 terminated in the loop, the problem goes away.

> buffer = (char *) safe_realloc (buffer, new_buffer_size * sizeof (char));
1. Why are you casting the alloc functions in C anyway - see the FAQ
2. I assume this is just a thin wrapper around realloc

If you do p = realloc ( p, newsize ); and it fails (returns NULL) then your code is broken and you have a memory leak.
It is much better to write

Code:

void *temp = realloc ( p, newsize );
if ( temp != NULL ) {
  p = temp;
} else {
  // panic, no more memory available, but p is still valid.
  // options could be
  // 1. free(p) and bail with return NULL
  // 2. return p "as is"
  // something else
}

Wrong.

BTW, NULL is for pointers, NUL is the nul-terminating character, 0, '\0'...