the public flockfile interface is significantly heavier because it has
to handle the possibility of caller returning or thread exiting while
holding the lock.
the text of the specification for getopt's handling of options that
require an argument, which requires updating optarg and optind, does
not exclude the error case where the end of the argument list has been
reached. in that case, it is expected that optarg be assigned
argv[argc] (normally null) and optind be incremented by 2, resulting
in a value of argc+1.
the ':' in optstring has special meaning as a flag applying to the
previous option character, or to getopt's error handling behavior when
it appears at the beginning. don't also accept a "-:" option based on
its presence.
getopt is only specified to modify optopt on error, and some software
apparently infers an error from optopt!=0.
getopt_long is changed analogously. the resulting behavior differs
slightly from the behavior of the GNU implementation of getopt_long,
which keeps an internal shadow copy of optopt and copies it to the
public one on return, but since the GNU implementation also exhibits
this shadow-copy behavior for plain getopt where is is non-conforming,
I think this can reasonably be considered a bug rather than an
intentional behavior that merits mimicing.
like fputs (see commit 10a17dfbad), the
message printing code for getopt assumed that fwrite only returns 0 on
failure, but it can also happen on success if the total length to be
written is zero. programs with zero-length argv[0] were affected.
commit 500c6886c6 introduced this
problem in getopt by fixing the fwrite behavior to conform to the
requirements of ISO C. previously the wrong expectations of the getopt
code were met by the fwrite implementation.
if writing the error message fails, POSIX requires that ferror(stderr)
be set. and as a function that operates on a stdio stream, getopt is
required to lock the stream it uses, stderr.
fwrite calls are used instead of fprintf since there is a demand from
some users not to pull in heavy stdio machinery via getopt. this
mimics the original code using write.
in the case where an initial '+' was passed in optstring (a
getopt_long feature to suppress argv permutation), getopt would fail
to see a possible subsequent ':', resulting in incorrect handling of
missing arguments.
the previous hard-coded offsets of +1 and +2 contained a hidden
assumption that the option character matched was single-byte, despite
this implementation of getopt attempting to support multibyte option
characters. this patch reworks the matching logic to leave the final
index pointing just past the matched character so that fixed offsets
can be used to check for ':'.
this is a GNU extension, activated by including '-' as the first
character of the options string, whereby non-option arguments are
processed as if they were arguments to an option character '\1' rather
than ending option processing.
Processing an option character with optional argument fails if the
option is last on the command line. This happens because the
if (optind >= argc) check runs first before testing for optional
argument.
this extension is not incompatible with the standard behavior of the
function, not expensive, and avoids requiring a replacement getopt
with full GNU extensions for a few important apps including busybox's
sed with the -i option.
GNU used several extensions that were incompatible with C99 and POSIX,
so they used alternate names for the standard functions.
The result is that we need these to run standards-conformant programs
that were linked with glibc.
based on proposed patches by Daniel Cegiełka, with minor changes:
- use a weak symbol for optreset so it doesn't clash with namespace
- also reset optpos (position in multi-option arg like -lR)
- also make getopt_long support reset
Rich Felker
Gianluca Anzolin
Felix Fietkau
Isaac Dunham