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Groups > comp.lang.c > #101421
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Correct way of doing string manipulation functions |
| Date | 2017-01-11 03:21 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <874m16th79.fsf@bsb.me.uk> (permalink) |
| References | <f6babbd9-c6df-4b6c-a8e2-0a51531650d5@googlegroups.com> <daea44ac-dbd3-4716-9a95-9de308030a6c@googlegroups.com> |
fir <profesor.fir@gmail.com> writes:
> W dniu środa, 11 stycznia 2017 00:43:53 UTC+1 użytkownik Fernando
> D. Bozzo napisał:
>> Hi all,
>>
>> I'm starting at C but have a background on programmming in OOP.
>>
>> My question is about string manipulation functions and the correct/best/good way of doing this in C.
>>
>> I've made a function that returns just the filename of a given full path or url, which I use this way:
>>
>>
>> // Suppose argv[1] is "http://www.myserver.com/file.html"
>> char *text_out = justfname(argv[1]);
>> printf("justfname = [%s]\n", text_out);
>> free(text_out);
>>
>>
>>
>> /**
>> * Returns the filename without path
>> *
>> * Examples:
>> * justfname("c:\aaa\bbb\ccc\ddd.txt") => "ddd.txt"
>> * justfname("http://www.myserver.com/file.html") => "file.html"
>> */
>> char *justfname(char *text_in)
>> {
>> int len = strlen(text_in);
>> char *fname = NULL;
>> char *text_out = malloc(sizeof(text_in));
>> fname = strrchr(text_in, '/');
>> if (fname == NULL)
>> {
>> fname = strrchr(text_in, '\\');
>> if (fname == NULL)
>> {
>> fname = text_in;
>> }
>> else
>> {
>> fname++; // Advance address +1 (skip "\" char)
>> }
>> }
>> else
>> {
>> fname++; // Advance address +1 (skip "/" char)
>> }
>>
>> // Copy obtained data
>> strncpy(text_out, fname, len);
>>
>> return text_out;
>> }
>>
>>
>>
>> So my questions are:
>> 1) Is this implementation ok/correct, or is there a better way of doing it?
>> 2) Is usually the caller who is responsible for freeing the used pointers on the called functions?
>> 3) When using pointers, are they normally created with malloc (heap) in habitual programming, or automatic var pointers (stack) are habitual too?
>>
>> Thanks!
>
> your implementation is wrong in many aspects
> (firstly i dont think it works at all, returning
> mallocked ram is also very bad, also your names
> are not ok, esp "fname" ... and more)
>
> in such simple case (where you sure name will be always at the end
> after last \ or / , and you will be using this name only to read not
> to modify (all sane apis will be ok with that last assumption)) you
> can just return pointer to first char of the name, so you will only
> need to find it
You also have to be sure that the lifetime of the returned pointer is
not used after the end of the array's life.
> char *ScanForPathOrURLName(char *text_in)
You can help document some of the assumption by using const:
const char *ScanForPathOrURLName(const char *text_in)
> {
> int k = strlen(text_in) - 1; //set on last char
This does not handle an empty input (""). And it's not the most
portable because size_t values can be larger than an int can represent.
You may be ruling out those possibilities, but it's good to document
such assumption in a comment.
> for(; k>=0; k--) //go down till first
> {
> if( text_in[k] == '\\' ) break;
> if( text_in[k] == '/' ) break;
> }
> return text_in + k + 1 ;
> }
I think the answer for "c:file" should be "path" rather than "c:file".
Another way:
const char *file_ptr = text_in;
for (const char *cp = text_in; *cp; cp++)
if (*cp == '/' || *cp == '\\' || *cp == ':')
file_ptr = cp;
return file_ptr + (file_ptr != text_in);
though maybe less tricksy would be
const char *file_ptr = 0;
for (const char *cp = text_in; *cp; cp++)
if (*cp == '/' || *cp == '\\' || *cp == ':')
file_ptr = cp;
return file_ptr ? text_in : file_ptr + 1;
<snip>
--
Ben.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-10 15:43 -0800
Re: Correct way of doing string manipulation functions "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-10 19:36 -0500
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-11 03:41 +0000
Re: Correct way of doing string manipulation functions James Kuyper <jameskuyper@verizon.net> - 2017-01-11 07:19 -0500
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:36 -0800
Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 16:41 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 16:54 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:38 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-11 18:24 -0800
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-11 03:38 +0000
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 20:02 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 20:28 -0800
Re: Correct way of doing string manipulation functions Ian Collins <ian-news@hotmail.com> - 2017-01-11 18:19 +1300
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-11 02:40 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 20:18 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:37 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-11 18:23 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-11 01:12 +0000
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-11 11:59 +0000
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:39 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-10 17:55 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 18:21 -0800
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-11 03:21 +0000
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-11 07:33 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-11 07:43 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-11 15:50 +0000
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-11 08:07 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:46 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 03:04 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 03:37 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 05:47 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 06:14 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 06:34 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 07:38 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 07:59 -0800
Re: Correct way of doing string manipulation functions Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-14 22:24 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-15 03:30 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-15 03:52 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-15 04:23 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:42 -0800
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-10 19:19 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:40 -0800
Re: Correct way of doing string manipulation functions Barry Schwarz <schwarzb@dqel.com> - 2017-01-10 20:31 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:45 -0800
Re: Correct way of doing string manipulation functions Gareth Owen <gwowen@gmail.com> - 2017-01-11 17:20 +0000
Re: Correct way of doing string manipulation functions "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 12:38 -0500
Strings as first class citizens (Was: Correct way of doing string manipulation functions) gazelle@shell.xmission.com (Kenny McCormack) - 2017-01-11 17:53 +0000
Re: Strings as first class citizens (Was: Correct way of doing string manipulation functions) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-11 12:46 -0800
Re: Strings as first class citizens (Was: Correct way of doing string manipulation functions) fir <profesor.fir@gmail.com> - 2017-01-11 14:40 -0800
Re: Strings as first class citizens (Was: Correct way of doing string manipulation functions) Robert Wessel <robertwessel2@yahoo.com> - 2017-01-11 18:12 -0600
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-11 09:56 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:48 -0800
Re: Correct way of doing string manipulation functions Thiago Adams <thiago.adams@gmail.com> - 2017-01-11 12:09 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 15:00 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 15:11 -0800
Re: Correct way of doing string manipulation functions "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 19:03 -0500
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 02:46 -0800
Re: Correct way of doing string manipulation functions Barry Schwarz <schwarzb@dqel.com> - 2017-01-12 00:08 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 03:02 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 11:38 +0000
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-12 13:51 +0000
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 14:41 +0000
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 09:32 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 18:15 +0000
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-12 11:46 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 13:52 -0800
Re: Correct way of doing string manipulation functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-12 16:50 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 00:59 +0000
Re: Correct way of doing string manipulation functions raltbos@xs4all.nl (Richard Bos) - 2017-01-13 08:59 +0000
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 13:07 +0000
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-13 10:11 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-13 18:49 +0000
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 08:43 -0800
Re: Correct way of doing string manipulation functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-13 09:45 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 18:17 +0000
Re: Correct way of doing string manipulation functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-13 10:30 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 18:48 +0000
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 11:02 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 19:15 +0000
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 12:18 -0800
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-13 12:14 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 12:49 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:19 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 10:46 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 11:55 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 10:41 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 10:51 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 12:28 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:07 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 13:29 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-13 21:45 +0000
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:59 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 15:08 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 14:13 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:47 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 08:02 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-12 07:50 -0800
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-12 08:37 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 09:41 -0800
Re: Correct way of doing string manipulation functions Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 17:39 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-13 18:02 -0800
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