collinm said:
hi
here my code
FILE *fp;
char *line[2];
#define LINE_MAX 30
fp = fopen("test1.txt", "r");
if ( ( line[0] = malloc( LINE_MAX) + 1) == NULL )
exit( EXIT_FAILURE );
fgets(line[0], LINE_MAX, fp);
fclose(fp);
fp = fopen("test2.txt", "r");
if ( ( line[1] = malloc( LINE_MAX) + 1) == NULL )
exit( EXIT_FAILURE );
fgets(line[1], LINE_MAX, fp);
fclose(fp);
are there a way to remove \0 for line[0] and line[1]?
I am not sure what you are asking, but it *might*
be about one or another of these issues:
- The malloc() calls and the way you test for their
success are wrong. Look carefully: You ask malloc() for
LINE_MAX bytes, then you add 1 to whatever value malloc()
returns, then you store the sum in line[0] or line[1],
and finally you compare the sum to NULL. If malloc()
succeeds, line[0] or line[1] points to the second byte
of the allocated area, which is probably not what you
want -- in particular, you need to write free(line[0]-1)
when you release the area. If malloc() fails, adding 1
to NULL produces undefined behavior -- the most likely
outcome is that you will get a sum that is not equal to
NULL but is useless because "it doesn't point anywhere."
- You might have intended malloc(LINE_MAX + 1) instead
of malloc(LINE_MAX) + 1; if so, that would be correct from
the standpoint of memory management. However, it would be
unnecessary because fgets() will never attempt to store
anything in that "extra" byte. The second argument to
fgets() is the entire length of the buffer *including*
space for the '\0' fgets() will store; fgets() will store
at most LINE_MAX characters *including* the '\0'.
- When you say you want to "remove \0," do you mean
that you want to eliminate the "+1" from the allocations?
If that's it, go ahead: as mentioned above, fgets() will
not store more bytes than its second argument indicates.
- ... or do you actually want to "remove" the '\0'
that fgets() stores after the end of each input line?
That seems a very stupid and dangerous thing to do, but
if you really want you can overwrite the '\0' with a
different character:
*strchr(line[0], '\0') = 'X';
- ... or do you want to remove the '\n' (not '\0')
at the end of the input line? That makes more sense,
since the trailing '\n' is often not wanted. You need
to be just a little bit careful, though, because if the
input line is too long for the buffer fgets() will store
only the first part of it and there will be no '\n' to
"remove." Here's one way to do it:
char *p;
...
p = strchr(line[0], '\n');
if (p != NULL)
*p = '\0';
.... and here's a shorter alternative using a less familiar
function:
line[0][ strcspn(line[0], "\n") ] = '\0';
- Finally, it is a good thing that you are careful to
check for failure of malloc(), even though you have done
it incorrectly. However, it is a bad thing that you have
*not* checked for failure of fopen() or for failure of
fgets()! High-tech motion-sensing locks on your attic
windows do not improve the security of your house if you
leave the front door hanging open.
