Problem with string manipulation

[aqazi]

Hi folks

I am trying to write a program which acts like a p2p server. When the
program starts it reads a file from whereit will read broadcast IP
address, port and another port number. Now I am trying skip the
comments and empty lines by saying if there is newline or # sign at the
first charecter of a line then to skip the line.But the problem is the
program is not working.

I am using the following code:

line = malloc(sizeof (char) *SIZE_OF_LINE);

while(fgets(lin e, SIZE_OF_LINE + 1, fp) != NULL)
{
i f(line[0] != '#' || line[0] != '\n')
{
fprintf(stderr, "i am here\n");
fprintf(stderr, "%s", line);
strcpy(tmpEntry , strtok(line, ":"));
strcpy(tmpValue , strtok(NULL, "\n"));
fprintf(stderr, "\t%s", tmpEntry);
fprintf(stderr, "\t: %s\n", tmpValue);
}
}

and the file the program is reading is:

############### ############### ############### ############### ############### ##
# P2P Conf File
#Please Don't modify this file as this is file is used to
#create all required sockets
# Author : Ahetesham Qazi
############### ############### ############### ############### ############### ##

Brodcast_IP:192 .168.1.255
Brodcast_Port:3 0001
Comm_Port:30101

The program should skip the first seven lines but the problem it's not
skipping. and when it's trying to tokenize the first line and then
printing it it's giving me segmentation fault.

Any suggetion would be greatly appreciated
Thanks
Ahetesham Qazi

[Richard Heathfield]

aq***@inbox.com said:

if(line[0] != '#' || line[0] != '\n')

How many characters can you think of that will fail this condition?

Read it out loud. If this character is not a hash, OR it is not a newline...

So a hash PASSES the test because it is not a newline, and a newline PASSES
the test because it is not a hash.

You meant to use && rather than ||

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Gordon Burditt]

>I am trying to write a program which acts like a p2p server. When the

>program starts it reads a file from whereit will read broadcast IP
address, port and another port number. Now I am trying skip the
comments and empty lines by saying if there is newline or # sign at the
first charecter of a line then to skip the line.

....

>I am using the following code:

line = malloc(sizeof (char) *SIZE_OF_LINE);

while(fgets(li ne, SIZE_OF_LINE + 1, fp) != NULL)
{
i f(line[0] != '#' || line[0] != '\n')

A newline is not equal to '#'.
A # is not equal to '\n'.
Another character is not equal to either.
In other words, the condition is always true.

Do you really want to use OR here?

[aqazi]

Richard Heathfield wrote:

aq***@inbox.com said:

if(line[0] != '#' || line[0] != '\n')

How many characters can you think of that will fail this condition?

Read it out loud. If this character is not a hash, OR it is not a newline...

So a hash PASSES the test because it is not a newline, and a newline PASSES
the test because it is not a hash.

You meant to use && rather than ||

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

Thanks for the solution. Actually this is a strictly predefined file.
So whithout the actual data
the only charecter can be at the start of the file is "#" or "\n"
Ahetesham Qazi

[Richard Heathfield]

aq***@inbox.com said:

>
Richard Heathfield wrote:

>aq***@inbox.com said:

if(line[0] != '#' || line[0] != '\n')

How many characters can you think of that will fail this condition?

Read it out loud. If this character is not a hash, OR it is not a
newline...

So a hash PASSES the test because it is not a newline, and a newline
PASSES the test because it is not a hash.

You meant to use && rather than ||

Thanks for the solution. Actually this is a strictly predefined file.
So whithout the actual data
the only charecter can be at the start of the file is "#" or "\n"

Nevertheless, all characters, *including* hash and newline, will pass your
existing test, the one that is intended to filter them out. When you change
the || to && the filter will have the desired effect.
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Nils O. Selåsdal]

aq***@inbox.com wrote:

Hi folks

I am trying to write a program which acts like a p2p server. When the
program starts it reads a file from whereit will read broadcast IP
address, port and another port number. Now I am trying skip the
comments and empty lines by saying if there is newline or # sign at the
first charecter of a line then to skip the line.But the problem is the
program is not working.

I am using the following code:

line = malloc(sizeof (char) *SIZE_OF_LINE);

while(fgets(lin e, SIZE_OF_LINE + 1, fp) != NULL)

Do not lie to fgets. You only have storage for
SIZE_OF_LINE chars, not SIZE_OF_LINE + 1.

[Nick Keighley]

aq***@inbox.com wrote:

line = malloc(sizeof (char) *SIZE_OF_LINE);

sizeof(char) is by definition 1, *always*, so this can be reduced to

line = malloc (SIZE_OF_LINE);
--
Nick Keighley

[Richard Heathfield]

Nick Keighley said:

aq***@inbox.com wrote:

>line = malloc(sizeof (char) *SIZE_OF_LINE);

sizeof(char) is by definition 1, *always*, so this can be reduced to

line = malloc (SIZE_OF_LINE);

That's one perfectly sensible approach. Here's another:

line = malloc(SIZE_OF_ LINE * sizeof *line);

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Ancient_Hacker]

aq***@inbox.com wrote:

line = malloc(sizeof (char) *SIZE_OF_LINE);

This would be a bit safer as: line = malloc( sizeof( *line ) );

while(fgets(lin e, SIZE_OF_LINE + 1, fp) != NULL)

similarly: while(fgets(lin e, sizeof( *line ), fp) != NULL)

if(line[0] != '#' || line[0] != '\n')

Several things amiss here:

(1) Are you sure if line[0] has been set? Yes, fgets() USUALLY puts
in a "\n", but not in every case.
You should do something like this first: : if( strlen(line) 0 ) {
....

(2) The tests are backwards.. It's more obvious if you write:

if( line[0] == '#' || line[0] == '\n' ) { /* ignore this line */ }
else { /* process it */
...
}

(3) What if the user accidentally types a space or tab, either leading
or trailing the line? Wouldnt hurt to handle these cases too.
(3) You're being awfully optimistic about what's in the file. I'd add
several tests to ensure that strtok finds what you expect, and the
length of the token doesnt overflow the destination. What you have
right now is an excellent way for somebody to crash or own your server
with a buffer overflow if they get write access to this file.

[Richard Heathfield]

Ancient_Hacker said:

>
aq***@inbox.com wrote:

>line = malloc(sizeof (char) *SIZE_OF_LINE);

This would be a bit safer as: line = malloc( sizeof( *line ) );

Er, no it wouldn't.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)