string splitting

[Andrea]

I want to write a program that:

char * strplit(char* str1, char *str2, char * stroriginal,int
split_point)

that take stroriginal and split in the split_point element of the
string the string into two other strings,

example:

"Hello World"
i want to split this string into "Hello " "World"



thanks in advance,
andrea

 

[Richard Heathfield]

Andrea said:

I want to write a program that:

char * strplit(char* str1, char *str2, char * stroriginal,int
split_point)

that take stroriginal and split in the split_point element of the
string the string into two other strings,

example:

"Hello World"
i want to split this string into "Hello " "World"

What's stopping you? What have you tried? (And with whom lies the
responsibility for storage allocation - the caller or the splitter?)

 

[Ian Malone]

Andrea said:


What's stopping you?

An inappropriate prototype?
char * strplit(char* str1, char *str2, char * stroriginal,
int split_point)

Questions for the OP:
What should be passed in str1, str2, stroriginal and
split_point? What is the significance of the return
value going to be?

As written I suspect that you plan to put the two sub-
strings into the memory pointed to by str1 and str2,
how will your function know that the objects pointed
to by these are large enough to hold the sub-strings?

 

[santosh]

I want to write a program that:

char * strplit(char* str1, char *str2, char * stroriginal,int
split_point)

that take stroriginal and split in the split_point element of the
string the string into two other strings,

example:

"Hello World"
i want to split this string into "Hello " "World"

Please post your attempt. Additionally what does the return value
point to? It's also perhaps better to const qualify the pointer to the
original string since your function need not modify it. You also need
to decide whether memory allocation for str1 and str2 should be done
in the caller or in the callee.

 

[Daniel Rudy]

At about the time of 2/21/2007 3:52 AM, Andrea stated the following:

I want to write a program that:

char * strplit(char* str1, char *str2, char * stroriginal,int
split_point)

that take stroriginal and split in the split_point element of the
string the string into two other strings,

example:

"Hello World"
i want to split this string into "Hello " "World"



thanks in advance,
andrea

Here's a hint: strsep.


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[Ben Pfaff]

Here's a hint: strsep.

strsep is not in the standard C library, so the OP may well not
have it available to him.

 

[Tydr Schnubbis]

strsep is not in the standard C library, so the OP may well not
have it available to him.

strtok does basically the same thing. But this looks a bit like
homework anyway.

 

[santosh]

At about the time of 2/21/2007 3:52 AM, Andrea stated the following:

Here's a hint: strsep.

The OP probably wants to implement the function himself as a learning
exercise. Use an existing function would defeat that purpose.

 

[Richard Bos]

strtok does basically the same thing.

Almost. strtok won't split "hello world", but it will split an array
containing those characters.

But this looks a bit like homework anyway.

More than a bit.

Richard

 

[u plz]

The OP probably wants to implement the function himself as a learning
exercise. Use an existing function would defeat that purpose.

Also the fact that strsep in not defined in the C standard means that the
OP might not be able to use it anyway.

-Alok

 

[Daniel Rudy]

At about the time of 2/21/2007 1:09 PM, Ben Pfaff stated the following:

strsep is not in the standard C library, so the OP may well not
have it available to him.

It's not?


STRSEP(3) FreeBSD Library Functions Manual STRSEP(3)

NAME
strsep -- separate strings

LIBRARY
Standard C Library (libc, -lc)

SYNOPSIS
#include <string.h>

char *
strsep(char **stringp, const char *delim);

DESCRIPTION
The strsep() function locates, in the string referenced by *stringp, the
first occurrence of any character in the string delim (or the terminating
`\0' character) and replaces it with a `\0'. The location of the next
character after the delimiter character (or NULL, if the end of the
string was reached) is stored in *stringp. The original value of
*stringp is returned.

An ``empty'' field (i.e., a character in the string delim occurs as the
first character of *stringp) can be detected by comparing the location
referenced by the returned pointer to `\0'.

If *stringp is initially NULL, strsep() returns NULL.

EXAMPLES
The following uses strsep() to parse a string, containing tokens delim-
ited by white space, into an argument vector:

char **ap, *argv[10], *inputstring;

for (ap = argv; (*ap = strsep(&inputstring, " \t")) != NULL
if (**ap != '\0')
if (++ap >= &argv[10])
break;

SEE ALSO
memchr(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strspn(3),
strstr(3), strtok(3)

HISTORY
The strsep() function is intended as a replacement for the strtok() func-
tion. While the strtok() function should be preferred for portability
reasons (it conforms to ISO/IEC 9899:1990 (``ISO C90'')) it is unable to
handle empty fields, i.e., detect fields delimited by two adjacent delim-
iter characters, or to be used for more than a single string at a time.
The strsep() function first appeared in 4.4BSD.

FreeBSD 6.2 June 9, 1993 FreeBSD 6.2


I guess it's not, but it probably should be... 4.4BSD though is the
original version that FreeBSD is based on, so the function has been
around for a long time.


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[matevzb]

At about the time of 2/21/2007 1:09 PM, Ben Pfaff stated the following:

It's not?

STRSEP(3) FreeBSD Library Functions Manual STRSEP(3)

NAME
strsep -- separate strings

LIBRARY
Standard C Library (libc, -lc)

This usually refers to libc, which may contain a lot more than ISO C
specifies (check strdup() for example). HP-UX man pages are really
useful in this area as they contain a "STANDARDS CONFORMANCE" section,
listing the standards that a function conforms to, e.g.:
strcoll(): AES, SVID3, XPG3, XPG4, ANSI C
strdup(): SVID2, SVID3

HISTORY
The strsep() function is intended as a replacement for the strtok() func-
tion. While the strtok() function should be preferred for portability
reasons (it conforms to ISO/IEC 9899:1990 (``ISO C90'')) it is unable to
handle empty fields, i.e., detect fields delimited by two adjacent delim-
iter characters, or to be used for more than a single string at a time.
The strsep() function first appeared in 4.4BSD.

FreeBSD 6.2 June 9, 1993 FreeBSD 6.2

I guess it's not, but it probably should be... 4.4BSD though is the
original version that FreeBSD is based on, so the function has been
around for a long time.

It didn't even get into POSIX/SUS, why should it be in C?

 

[Richard Heathfield]

Daniel Rudy said:

At about the time of 2/21/2007 1:09 PM, Ben Pfaff stated the
following:

It's not?
No.

STRSEP(3) FreeBSD Library Functions Manual

What makes you think FreeBSD get to decide what is in the standard C
library?

$ grep -i strsep c89.txt
$

 

[CBFalconer]

.... snip ...

This usually refers to libc, which may contain a lot more than ISO
C specifies (check strdup() for example). HP-UX man pages are
really useful in this area as they contain a "STANDARDS
CONFORMANCE" section, listing the standards that a function
conforms to, e.g.: strcoll(): AES, SVID3, XPG3, XPG4, ANSI C
strdup(): SVID2, SVID3


It didn't even get into POSIX/SUS, why should it be in C?

You can try the following. The source code has been published here
before, if you want it search google.

/* ------- file toksplit.h ----------*/
#ifndef H_toksplit_h
# define H_toksplit_h

# ifdef __cplusplus
extern "C" {
# endif

#include <stddef.h>

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

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

Returns: a pointer past the terminating tokchar.

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

released to Public Domain, by C.B. Falconer.
Published 2006-02-20. Attribution appreciated.
*/

const char *toksplit(const char *src, /* Source of tokens */
char tokchar, /* token delimiting char */
char *token, /* receiver of parsed token */
size_t lgh); /* length token can receive */
/* not including final '\0' */

# ifdef __cplusplus
}
# endif
#endif
/* ------- end file toksplit.h ----------*/

 

[Daniel Rudy]

At about the time of 2/23/2007 4:42 AM, Richard Heathfield stated the
following:

Daniel Rudy said:


What makes you think FreeBSD get to decide what is in the standard C
library?

$ grep -i strsep c89.txt
$

I didn't say that FreeBSD should decide what goes into the C library.
What I was getting at is the fact that since the function has been
around along time, and that it's superior to strtok (strsep handles
situations that strtok doesn't), why hasn't it been included (at least
in the POSIX standard if not the C standard)?

Now I'm not too up on what functions comprise the standard C library and
what doesn't, reading THIS man page you can see the cause of confusion:

STRTOK(3) FreeBSD Library Functions Manual

NAME
strtok, strtok_r -- string tokens

LIBRARY
Standard C Library (libc, -lc)

SYNOPSIS
#include <string.h>

char *
strtok(char *str, const char *sep);

char *
strtok_r(char *str, const char *sep, char **last);

DESCRIPTION
This interface is obsoleted by strsep(3).

The strtok() function is used to isolate sequential tokens in a
null-terminated string, str. These tokens are separated in the


I cut it short because of its length. But in the bugs section,

BUGS
The System V strtok(), if handed a string containing only delimiter
char-
acters, will not alter the next starting point, so that a call to
strtok() with a different (or empty) delimiter string may return a
non-NULL value. Since this implementation always alters the next
start-
ing point, such a sequence of calls would always return NULL.


Oh well. Learn something new every day.


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[Ben Pfaff]

Now I'm not too up on what functions comprise the standard C library and
what doesn't, reading THIS man page you can see the cause of confusion:

STRTOK(3) FreeBSD Library Functions Manual

NAME
strtok, strtok_r -- string tokens

LIBRARY
Standard C Library (libc, -lc)

File a bug against the FreeBSD manpage then. It's wrong.

 

[CBFalconer]

Daniel Rudy said:
.... snip ...


What makes you think FreeBSD get to decide what is in the standard
C library?

$ grep -i strsep c89.txt
$

and similarly for N869.txt (C99)

 

[CBFalconer]

.... snip ...

I didn't say that FreeBSD should decide what goes into the C library.
What I was getting at is the fact that since the function has been
around along time, and that it's superior to strtok (strsep handles
situations that strtok doesn't), why hasn't it been included (at
least in the POSIX standard if not the C standard)?

Who says it is superior? Another candidate is toksplit (detailed
elsethread). It all depends on what is required. There is no
pressing need for any of these in the standard library, since they
can all easily be written in standard C.

 

[Keith Thompson]

File a bug against the FreeBSD manpage then. It's wrong.

The phrase "Standard C Library" doesn't necessarily imply that the
function is defined by the C standard. Probably "libc" implements
(most of) the functions defined by the C standard, plus some others.
(I suspect the math functions are in a different library.)

 

[Charlton Wilbur]

BP> File a bug against the FreeBSD manpage then. It's wrong.

Depends on which standard is being referred to, and which function;
strtok() is in fact standard C. The word "standard" may also not be
used in the c.l.c sense of ISO/ANSI standard C, but to refer to the C
library generally shipped with FreeBSD.

On the other hand, the BSDs I have access to at this very moment -- OS
X and OpenBSD - both correctly note in the relevant manpages that
strsep() is an improved version of the standard strtok(), and that
strtok() is ANSI/ISO standard C while strtok_r and strsep are not. So
this is most likely a FreeBSD issue.

Charlton