strtok question

[Stu Cazzo]

Hi all,
I have a question on why strtok is doing what it's doing for my
splitString( string2 ); call.

Below is the output for the entire program:

token was: word1
token was: word2
token was: word3
token was: word1
token was: word3
empty field found - token <(null)>


The splitString( string1 ); works as expected, 3 tokens are found.
The splitString( string2 ); does not work as I expected.
I was expecting this:

token was: word1
empty field found - token <(null)>
token was: word3

Why does it not see the empty field for lineToken2?
Is there a better way to strip out the tokens for the case I have
where
there is no space between my delimiter?

-------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void splitString( char *string )
{
const char lineDelimiter[] = ",";
char *lineToken1;
char *lineToken2;
char *lineToken3;

lineToken1 = strtok( string, lineDelimiter );
if ( lineToken1 == '\0' )
{
printf("empty field found - token <%s>\n", lineToken1);
}
else
{
printf("token was: %s\n", lineToken1);
}

lineToken2 = strtok( NULL, lineDelimiter );
if ( lineToken2 == '\0' )
{
printf("empty field found - token <%s>\n", lineToken2);
}
else
{
printf("token was: %s\n", lineToken2);
}

lineToken3 = strtok( NULL, lineDelimiter );
if ( lineToken3 == '\0' )
{
printf("empty field found - token <%s>\n", lineToken3);
}
else
{
printf("token was: %s\n", lineToken3);
}

}



int main (int argc, const char **argv)
{
char string1[] = "word1,word2,wo rd3";
char string2[] = "word1,,wor d3";

splitString( string1 );
splitString( string2 );

return( 1 );

}

[Jens Thoms Toerring]

Re: strtok question

Stu Cazzo <SCazzo@gmail.c omwrote:

Hi all,
I have a question on why strtok is doing what it's doing for my
splitString( string2 ); call.

Below is the output for the entire program:

token was: word1
token was: word2
token was: word3
token was: word1
token was: word3
empty field found - token <(null)>

The splitString( string1 ); works as expected, 3 tokens are found.
The splitString( string2 ); does not work as I expected.
I was expecting this:

token was: word1
empty field found - token <(null)>
token was: word3

Why does it not see the empty field for lineToken2?

Because that's not how strtok() works. The man page on my machine
for strtok() actually makes it rather clear:

A sequence of two or more contiguous delimiter characters in the
parsed string is considered to be a single delimiter. Delimiter
characters at the start or end of the string are ignored. Put
another way: the tokens returned by strtok() are always non-empty
strings.

So if you have more than one ',' in a row all of them are treated
the same as a single ','.

Is there a better way to strip out the tokens for the case I have
where there is no space between my delimiter?

I guess you will have to write your own function for that, probably
repeatedly using strchr() or strstr().

Regards, Jens
--
\ Jens Thoms Toerring ___ jt@toerring.de
\______________ ____________ http://toerring.de

[CBFalconer]

Re: strtok question

Jens Thoms Toerring wrote:

Stu Cazzo <SCazzo@gmail.c omwrote:
>

.... snip ...

>

>The splitString( string1 ); works as expected, 3 tokens are found.
>The splitString( string2 ); does not work as I expected.

>

.... snip ...

>

>Why does it not see the empty field for lineToken2?

>
Because that's not how strtok() works. The man page on my machine
for strtok() actually makes it rather clear:
>

.... snip ...

>

>Is there a better way to strip out the tokens for the case I have
>where there is no space between my delimiter?

>
I guess you will have to write your own function for that, probably
repeatedly using strchr() or strstr().

Try this:

/* ------- file tknsplit.c ----------*/
#include "tknsplit.h "

/* copy over the next tkn from an input string, after
skipping leading blanks (or other whitespace?). The
tkn is terminated by the first appearance of tknchar,
or by the end of the source string.

The caller must supply sufficient space in tkn to
receive any tkn, Otherwise tkns will be truncated.

Returns: a pointer past the terminating tknchar.

This will happily return an infinity of empty tkns if
called with src pointing to the end of a string. Tokens
will never include a copy of tknchar.

A better name would be "strtkn", except that is reserved
for the system namespace. Change to that at your risk.

released to Public Domain, by C.B. Falconer.
Published 2006-02-20. Attribution appreciated.
Revised 2006-06-13 2007-05-26 (name)
*/

const char *tknsplit(const char *src, /* Source of tkns */
char tknchar, /* tkn delimiting char */
char *tkn, /* receiver of parsed tkn */
size_t lgh) /* length tkn can receive */
/* not including final '\0' */
{
if (src) {
while (' ' == *src) src++;

while (*src && (tknchar != *src)) {
if (lgh) {
*tkn++ = *src;
--lgh;
}
src++;
}
if (*src && (tknchar == *src)) src++;
}
*tkn = '\0';
return src;
} /* tknsplit */

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


** Posted from http://www.teranews.com **

[Ben Bacarisse]

Re: strtok question

CBFalconer <cbfalconer@yah oo.comwrites:
<snip>

while (*src && (tknchar != *src)) {

<snip body>

}
if (*src && (tknchar == *src)) src++;

Some people might find that test confusing. It is certainly
belt-and-braces code.

--
Ben.

[CBFalconer]

Re: strtok question

Ben Bacarisse wrote:

CBFalconer <cbfalconer@yah oo.comwrites:
<snip>

> while (*src && (tknchar != *src)) {

<snip body>

> }
> if (*src && (tknchar == *src)) src++;

>
Some people might find that test confusing. It is certainly
belt-and-braces code.

You should have left the body. That code doesn't have the same
effect. Assuming I am correctly interpreting your message.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


** Posted from http://www.teranews.com **

[Antoninus Twink]

Re: strtok question

On 31 May 2008 at 23:37, Ben Bacarisse wrote:

CBFalconer <cbfalconer@yah oo.comwrites:
><snip>

> while (*src && (tknchar != *src)) {

><snip body>

> }
> if (*src && (tknchar == *src)) src++;

>
Some people might find that test confusing. It is certainly
belt-and-braces code.

Most people grow out of this sort of thing within a few months or so of
their initial child-like excitement at discovering a language with so
many side effects. Clarity and ease of debugging become more valuable
than a transient smug feeling of cleverness.

Actually I'm pretty tolerant of different people's ways of laying out
code, indenting and the rest, but CBF really does seem to have total
anti-taste when it comes to code formatting. Perhaps the most irritating
thing of all is

>} /* tknsplit */

This seems to me to be about as helpful as the infamous

i++; /* increment i by one */

[Richard]

Re: strtok question

Antoninus Twink <nospam@nospam. invalidwrites:

On 31 May 2008 at 23:37, Ben Bacarisse wrote:

>CBFalconer <cbfalconer@yah oo.comwrites:
>><snip>

>> while (*src && (tknchar != *src)) {

>><snip body>

>> }
>> if (*src && (tknchar == *src)) src++;

>>
>Some people might find that test confusing. It is certainly
>belt-and-braces code.

>
Most people grow out of this sort of thing within a few months or so of
their initial child-like excitement at discovering a language with so
many side effects. Clarity and ease of debugging become more valuable
than a transient smug feeling of cleverness.

I have to agree 100% with this statement. Some people seem to take
pleasure in obfuscating their code.

>
Actually I'm pretty tolerant of different people's ways of laying out
code, indenting and the rest, but CBF really does seem to have total
anti-taste when it comes to code formatting. Perhaps the most irritating
thing of all is
>

>>} /* tknsplit */

>
This seems to me to be about as helpful as the infamous
>
i++; /* increment i by one */

Again agreed.

[Ben Bacarisse]

Re: strtok question

CBFalconer <cbfalconer@yah oo.comwrites:

Ben Bacarisse wrote:

>CBFalconer <cbfalconer@yah oo.comwrites:
><snip>

>> while (*src && (tknchar != *src)) {

><snip body>

>> }
>> if (*src && (tknchar == *src)) src++;

>>
>Some people might find that test confusing. It is certainly
>belt-and-braces code.

>
You should have left the body.

It has no bearing on my point. Any loop body that terminates in the
normal way would do just as well. Maybe I should have said "<snip
body with no break statement>".

That code doesn't have the same
effect. Assuming I am correctly interpreting your message.

I think you missed the point. If you want the function to work when
tknchar might be 0, then if (tknchar == *src) src++; is enough. If
you don't want it to work when tknchar is 0 (as seems to be the case)
then if (*src) src++; is enough.

It is not in any way wrong, just as if (c == '\n' && c) is not really
wrong -- it just makes the reader do an unwarranted double take.

--
Ben.

[Ben Bacarisse]

Re: strtok question

Antoninus Twink <nospam@nospam. invalidwrites:

On 31 May 2008 at 23:37, Ben Bacarisse wrote:

>CBFalconer <cbfalconer@yah oo.comwrites:
>><snip>

>> while (*src && (tknchar != *src)) {

>><snip body>

>> }
>> if (*src && (tknchar == *src)) src++;

>>
>Some people might find that test confusing. It is certainly
>belt-and-braces code.

>
Most people grow out of this sort of thing within a few months or so of
their initial child-like excitement at discovering a language with so
many side effects. Clarity and ease of debugging become more valuable
than a transient smug feeling of cleverness.

I don't know what you mean in this case. I agree with the sentiment,
but what has it do with this example? How do you write this without
using side effects?

The reference to debugging makes me thing you object to the layout.
Would moving the increment of src down a line make it all OK?

Actually I'm pretty tolerant of different people's ways of laying out
code,

Ah. So you were commenting on the layout. What was the reference to
abusing side effects about?

--
Ben.