Messages in this thread | | | From | André Goddard Rosa <> | Date | Mon, 16 Nov 2009 10:21:48 -0200 | Subject | Re: [PATCH v5 10/12] string: factorize skip_spaces and export it to be generally available |
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Hi, Anders!
On Sun, Nov 15, 2009 at 7:51 PM, Anders Larsen <al@alarsen.net> wrote: > On 2009-11-15 21:02:15, Anonymous wrote: >> >> On Sun, Nov 15, 2009 at 08:33:29PM +0100, Anders Larsen wrote: >> > On 2009-11-15 08:15:03, André Goddard Rosa wrote: >> > >+char *skip_spaces(const char *str) >> > >+{ >> > >+ while (isspace(*str)) >> > >+ ++str; >> > >+ return (char *)str; >> > >+} >> >> Is there a good reason why the parameter 'str' is declared 'const' >> > when skip_spaces() returns a non-const pointer into str ? >> >Declaring return value as const won't let us modificate string after >> skipping spaces. Declaring parameter as non-const won't let us >> giving (const char *) to this function. So i think it is ok. > > skip_spaces() _implicitly_ casts away the 'const' of the parameter, > which may come as a (nasty) surprise to users of the function. > > Consider this (contrieved and buggy) example: > > const char* my_string = " do not modify me! "; > char* result = strcat(skip_spaces(my_string, "boom!")); > > The proposed implementation of skip_spaces() effectively prevents > the compiler from catching this obvious bug. >
I agree with the above comment. It's possible to make it differently char* skip_spaces(char *), but it's necessary to change many of its callers at the same time:
CC lib/argv_split.o lib/argv_split.c: In function ‘count_argc’: lib/argv_split.c:24: warning: passing argument 1 of ‘skip_spaces’ discards qualifiers from pointer target type include/linux/string.h:65: note: expected ‘char *’ but argument is of type ‘const char *’ lib/argv_split.c: In function ‘argv_split’: lib/argv_split.c:78: warning: passing argument 1 of ‘skip_spaces’ discards qualifiers from pointer target type include/linux/string.h:65: note: expected ‘char *’ but argument is of type ‘const char *’ ... CC lib/vsprintf.o lib/vsprintf.c: In function ‘vsscanf’: lib/vsprintf.c:1737: warning: passing argument 1 of ‘skip_spaces’ discards qualifiers from pointer target type include/linux/string.h:65: note: expected ‘char *’ but argument is of type ‘const char *’ lib/vsprintf.c:1738: warning: passing argument 1 of ‘skip_spaces’ discards qualifiers from pointer target type include/linux/string.h:65: note: expected ‘char *’ but argument is of type ‘const char *’ lib/vsprintf.c:1808: warning: passing argument 1 of ‘skip_spaces’ discards qualifiers from pointer target type include/linux/string.h:65: note: expected ‘char *’ but argument is of type ‘const char *’ lib/vsprintf.c:1850: warning: passing argument 1 of ‘skip_spaces’ discards qualifiers from pointer target type include/linux/string.h:65: note: expected ‘char *’ but argument is of type ‘const char *’
There are other functions following the same pattern presently:
char *strstr(const char *haystack, const char *needle); char *strchr(const char *s, int c); char *strrchr(const char *s, int c);
on both glibc and the kernel.
Thanks, André -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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