=encoding utf8 =head1 NAME perl5260delta - what is new for perl v5.26.0 =head1 DESCRIPTION This document describes the differences between the 5.24.0 release and the 5.26.0 release. =head1 Notice This release includes three updates with widespread effects: =over 4 =item * C no longer in C For security reasons, the current directory (C) is no longer included by default at the end of the module search path (C). This may have widespread implications for the building, testing and installing of modules, and for the execution of scripts. See the section L) from C >> for the full details. =item * C may now warn C now gives a deprecation warning when it fails to load a file which it would have loaded had C been in C. =item * In regular expression patterns, a literal left brace C should be escaped See L characters in regular expression patterns are no longer permissible>. =back =head1 Core Enhancements =head2 Lexical subroutines are no longer experimental Using the C feature introduced in v5.18 no longer emits a warning. Existing code that disables the C<:lexical_subs> warning category that the feature previously used will continue to work. The C feature has no effect; all Perl code can use lexical subroutines, regardless of what feature declarations are in scope. =head2 Indented Here-documents This adds a new modifier C to here-docs that tells the parser that it should look for C^\s*$DELIM\n/> as the closing delimiter. These syntaxes are all supported: modifier will strip, from each line in the here-doc, the same whitespace that appears before the delimiter. Newlines will be copied as-is, and lines that don't include the proper beginning whitespace will cause perl to croak. For example: if (1) { print Specifying two C characters to modify a regular expression pattern does everything that a single one does, but additionally TAB and SPACE characters within a bracketed character class are generally ignored and can be added to improve readability, like S>. Details are at Lx and Exx>. =head2 C, C, and C C exposes the capture buffers of the last match as an array. So C is C. This is a more efficient equivalent to code like C, and you don't have to keep track of the C either. This variable has no single character equivalent. Note that, like the other regex magic variables, the contents of this variable is dynamic; if you wish to store it beyond the lifetime of the match you must copy it to another array. C is equivalent to C (I, named captures). Other than being more self-documenting there is no difference between the two forms. C is equivalent to C (I, all named captures). Other than being more self-documenting there is no difference between the two forms. =head2 Declaring a reference to a variable As an experimental feature, Perl now allows the referencing operator to come after L|perlfunc/my>, L|perlfunc/state>, L|perlfunc/our>, or L|perlfunc/local>. This syntax must be enabled with C. It is experimental, and will warn by default unless C is in effect. It is intended mainly for use in assignments to references. For example: use experimental 'refaliasing', 'declared_refs'; my \$a = \$b; See L for more details. =head2 Unicode 9.0 is now supported A list of changes is at L. Modules that are shipped with core Perl but not maintained by p5p do not necessarily support Unicode 9.0. L<:normalize> does work on 9.0. =head2 Use of C}> uses the improved Script_Extensions property Unicode 6.0 introduced an improved form of the Script (C) property, and called it Script_Extensions (C). Perl now uses this improved version when a property is specified as just C}>. This should make programs more accurate when determining if a character is used in a given script, but there is a slight chance of breakage for programs that very specifically needed the old behavior. The meaning of compound forms, like C}> are unchanged. See L. =head2 Perl can now do default collation in UTF-8 locales on platforms that support it Some platforms natively do a reasonable job of collating and sorting in UTF-8 locales. Perl now works with those. For portability and full control, L<:collate> is still recommended, but now you may not need to do anything special to get good-enough results, depending on your application. See L: Collation: Text Comparisons and Sorting>. =head2 Better locale collation of strings containing embedded C characters In locales that have multi-level character weights, Cs are now ignored at the higher priority ones. There are still some gotchas in some strings, though. See L characters>. =head2 C subroutines for hash and array functions callable via reference The hash and array functions in the C namespace (C, C, C, C, C, C, C and C) can now be called with ampersand syntax (C) and via reference (C(\%hash) >>). Previously they could only be used when inlined. =head2 New Hash Function For 64-bit Builds We have switched to a hybrid hash function to better balance performance for short and long keys. For short keys, 16 bytes and under, we use an optimised variant of One At A Time Hard, and for longer keys we use Siphash 1-3. For very long keys this is a big improvement in performance. For shorter keys there is a modest improvement. =head1 Security =head2 Removal of the current directory (C) from C The perl binary includes a default set of paths in C. Historically it has also included the current directory (C) as the final entry, unless run with taint mode enabled (C). While convenient, this has security implications: for example, where a script attempts to load an optional module when its current directory is untrusted (such as F), it could load and execute code from under that directory. Starting with v5.26, C is always removed by default, not just under tainting. This has major implications for installing modules and executing scripts. The following new features have been added to help ameliorate these issues. =over =item * F There is a new F option, C (enabled by default) which builds a perl executable without C; unsetting this option using C reverts perl to the old behaviour. This may fix your path issues but will reintroduce all the security concerns, so don't build a perl executable like this unless you're I confident that such issues are not a concern in your environment. =item * C There is a new environment variable recognised by the perl interpreter. If this variable has the value 1 when the perl interpreter starts up, then C will be automatically appended to C (except under tainting). This allows you restore the old perl interpreter behaviour on a case-by-case basis. But note that this is intended to be a temporary crutch, and this feature will likely be removed in some future perl version. It is currently set by the C utility and C<:harness> to ease installation of CPAN modules which have not been updated to handle the lack of dot. Once again, don't use this unless you are sure that this will not reintroduce any security concerns. =item * A new deprecation warning issued by C. While it is well-known that C and C use C to search for the file to load, many people don't realise that C also searches C if the file is a relative path. With the removal of C, a simple C will fail to read in and execute C from the current directory. Since this is commonly expected behaviour, a new deprecation warning is now issued whenever C fails to load a file which it otherwise would have found if a dot had been in C. =back Here are some things script and module authors may need to do to make their software work in the new regime. =over =item * Script authors If the issue is within your own code (rather than within included modules), then you have two main options. Firstly, if you are confident that your script will only be run within a trusted directory (under which you expect to find trusted files and modules), then add C back into the path; I: BEGIN { my $dir = "/some/trusted/directory"; chdir $dir or die "Can't chdir to $dir: $!\n"; # safe now push @INC, '.'; } use "Foo::Bar"; # may load /some/trusted/directory/Foo/Bar.pm do "config.pl"; # may load /some/trusted/directory/config.pl On the other hand, if your script is intended to be run from within untrusted directories (such as F), then your script suddenly failing to load files may be indicative of a security issue. You most likely want to replace any relative paths with full paths; for example, do "foo_config.pl" might become do "$ENV{HOME}/foo_config.pl" If you are absolutely certain that you want your script to load and execute a file from the current directory, then use a C<.> prefix; for example: do "./foo_config.pl" =item * Installing and using CPAN modules If you install a CPAN module using an automatic tool like C, then this tool will itself set the C environment variable while building and testing the module, which may be sufficient to install a distribution which hasn't been updated to be dot-aware. If you want to install such a module manually, then you'll need to replace the traditional invocation: perl Makefile.PL && make && make test && make install with something like (export PERL_USE_UNSAFE_INC=1; \ perl Makefile.PL && make && make test && make install) Note that this only helps build and install an unfixed module. It's possible for the tests to pass (since they were run under C), but for the module itself to fail to perform correctly in production. In this case, you may have to temporarily modify your script until a fixed version of the module is released. For example: use Foo::Bar; { local @INC = (@INC, '.'); # assuming read_config() needs '.' in @INC $config = Foo::Bar->read_config(); } This is only rarely expected to be necessary. Again, if doing this, assess the resultant risks first. =item * Module Authors If you maintain a CPAN distribution, it may need updating to run in a dotless environment. Although C and other such tools will currently set the C during module build, this is a temporary workaround for the set of modules which rely on C being in C for installation and testing, and this may mask deeper issues. It could result in a module which passes tests and installs, but which fails at run time. During build, test, and install, it will normally be the case that any perl processes will be executing directly within the root directory of the untarred distribution, or a known subdirectory of that, such as F. It may well be that F or F will attempt to include local modules and configuration files using their direct relative filenames, which will now fail. However, as described above, automatic tools like F will (for now) set the C environment variable, which introduces dot during a build. This makes it likely that your existing build and test code will work, but this may mask issues with your code which only manifest when used after install. It is prudent to try and run your build process with that variable explicitly disabled: (export PERL_USE_UNSAFE_INC=0; \ perl Makefile.PL && make && make test && make install) This is more likely to show up any potential problems with your module's build process, or even with the module itself. Fixing such issues will ensure both that your module can again be installed manually, and that it will still build once the C crutch goes away. When fixing issues in tests due to the removal of dot from C, reinsertion of dot into C should be performed with caution, for this too may suppress real errors in your runtime code. You are encouraged wherever possible to apply the aforementioned approaches with explicit absolute/relative paths, or to relocate your needed files into a subdirectory and insert that subdirectory into C instead. If your runtime code has problems under the dotless C, then the comments above on how to fix for script authors will mostly apply here too. Bear in mind though that it is considered bad form for a module to globally add a dot to C, since it introduces both a security risk and hides issues of accidentally requiring dot in C, as explained above. =back =head2 Escaped colons and relative paths in PATH On Unix systems, Perl treats any relative paths in the C environment variable as tainted when starting a new process. Previously, it was allowing a backslash to escape a colon (unlike the OS), consequently allowing relative paths to be considered safe if the PATH was set to something like C\:.>. The check has been fixed to treat C as tainted in that example. =head2 New C switch is now required for PerlIO debugging output This is used for debugging of code within PerlIO to avoid recursive calls. Previously this output would be sent to the file specified by the C environment variable if perl wasn't running setuid and the C or C switches hadn't been parsed yet. If perl performed output at a point where it hadn't yet parsed its switches this could result in perl creating or overwriting the file named by C even when the C switch had been supplied. Perl now requires the C switch to be present before it will produce PerlIO debugging output. By default this is written to C, but can optionally be redirected to a file by setting the C environment variable. If perl is running setuid or the C switch was supplied, C is ignored and the debugging output is sent to C as for any other C switch. =head1 Incompatible Changes =head2 Unescaped literal C characters in regular expression patterns are no longer permissible You have to now say something like C or C to specify to match a LEFT CURLY BRACKET; otherwise, it is a fatal pattern compilation error. This change will allow future extensions to the language. These have been deprecated since v5.16, with a deprecation message raised for some uses starting in v5.22. Unfortunately, the code added to raise the message was buggy and failed to warn in some cases where it should have. Therefore, enforcement of this ban for these cases is deferred until Perl 5.30, but the code has been fixed to raise a default-on deprecation message for them in the meantime. Some uses of literal C occur in contexts where we do not foresee the meaning ever being anything but the literal, such as the very first character in the pattern, or after a C meaning alternation. Thus qr/{fee|{fie/ matches either of the strings C or C. To avoid forcing unnecessary code changes, these uses do not need to be escaped, and no warning is raised about them, and there are no current plans to change this. But it is always correct to escape C, and the simple rule to remember is to always do so. See L-- HERE> in mE%sE>. =head2 C return signature changed The value returned for C will no longer show information about the buckets allocated in the hash. It will simply return the count of used keys. It is thus equivalent to C. A form of backward compatibility is provided via L|Hash::Util/bucket_ratio> which provides the same behavior as C provided in Perl 5.24 and earlier. =head2 C returned from an lvalue subroutine C returned from an lvalue subroutine can no longer be assigned to in list context. sub foo : lvalue { keys(%INC) } (foo) = 3; # death sub bar : lvalue { keys(@_) } (bar) = 3; # also an error This makes the lvalue sub case consistent with C and C, which are also errors. L =head2 The C facility has been removed The special behaviour associated with assigning a value to this variable has been removed. As a consequence, the L pragma's default mode is no longer supported. If you still need to write your source code in encodings other than UTF-8, use a source filter such as L<:encoding> on CPAN or L's C option. =head2 C<:tmpnam> has been removed The fundamentally unsafe C interface was deprecated in Perl 5.22 and has now been removed. In its place, you can use, for example, the L<:temp> interfaces. =head2 require ::Foo::Bar is now illegal. Formerly, C would try to read F. Now any bareword require which starts with a double colon dies instead. =head2 Literal control character variable names are no longer permissible A variable name may no longer contain a literal control character under any circumstances. These previously were allowed in single-character names on ASCII platforms, but have been deprecated there since Perl 5.20. This affects things like C>, where I is a literal control (such as a C or C character) in the source code. =head2 C is no longer permissible in C The name of a character may no longer contain non-breaking spaces. It has been deprecated to do so since Perl 5.22. =head1 Deprecations =head2 String delimiters that aren't stand-alone graphemes are now deprecated For Perl to eventually allow string delimiters to be Unicode grapheme clusters (which look like a single character, but may be a sequence of several ones), we have to stop allowing a single character delimiter that isn't a grapheme by itself. These are unlikely to exist in actual code, as they would typically display as attached to the character in front of them. =head2 C> that maps to a printable is no longer deprecated This means we have no plans to remove this feature. It still raises a warning, but only if syntax warnings are enabled. The feature was originally intended to be a way to express non-printable characters that don't have a mnemonic (C and C are mnemonics for two non-printable characters, but most non-printables don't have a mnemonic.) But the feature can be used to specify a few printable characters, though those are more clearly expressed as the printable itself. See L. =head1 Performance Enhancements =over 4 =item * A hash in boolean context is now sometimes faster, I if (!%h) { ... } This was already special-cased, but some cases were missed (such as C), and even the ones which weren't have been improved. =item * New Faster Hash Function on 64 bit builds We use a different hash function for short and long keys. This should improve performance and security, especially for long keys. =item * readline is faster Reading from a file line-by-line with C or CE >> should now typically be faster due to a better implementation of the code that searches for the next newline character. =item * Assigning one reference to another, I C has been optimized in some cases. =item * Remove some exceptions to creating Copy-on-Write strings. The string buffer growth algorithm has been slightly altered so that you're less likely to encounter a string which can't be COWed. =item * Better optimise array and hash assignment: where an array or hash appears in the LHS of a list assignment, such as C, it's likely to be considerably faster, especially if it involves emptying the array/hash. For example, this code runs about a third faster compared to Perl 5.24.0: my @a; for my $i (1..10_000_000) { @a = (1,2,3); @a = (); } =item * Converting a single-digit string to a number is now substantially faster. =item * The C builtin is now slightly faster in many cases: in particular for the two specially-handled forms my @a = split ...; local @a = split ...; =item * The rather slow implementation for the experimental subroutine signatures feature has been made much faster; it is now comparable in speed with the traditional C. =item * Bareword constant strings are now permitted to take part in constant folding. They were originally exempted from constant folding in August 1999, during the development of Perl 5.6, to ensure that C would still apply to bareword constants. That has now been accomplished a different way, so barewords, like other constants, now gain the performance benefits of constant folding. This also means that void-context warnings on constant expressions of barewords now report the folded constant operand, rather than the operation; this matches the behaviour for non-bareword constants. =back =head1 Modules and Pragmata =head2 Updated Modules and Pragmata =over 4 =item * IO::Compress has been upgraded from version 2.069 to 2.074. =item * L<:tar> has been upgraded from version 2.04 to 2.24. =item * L has been upgraded from version 0.11 to 0.12. =item * L has been upgraded from version 0.27 to 0.29. The deprecation message for the C<:unique> and C<:locked> attributes now mention that they will disappear in Perl 5.28. =item * L has been upgraded from version 1.62 to 1.68. =item * L<:concise> has been upgraded from version 0.996 to 0.999. Its output is now more descriptive for C flags. =item * L<:debug> has been upgraded from version 1.23 to 1.24. =item * L<:deparse> has been upgraded from version 1.37 to 1.40. =item * L<:xref> has been upgraded from version 1.05 to 1.06. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 2.23 to 2.25. =item * L has been upgraded from version 0.42 to 0.47. =item * L has been upgraded from version 1.40 to 1.42. =item * L has been upgraded from version 1.43 to 1.44. =item * L<:raw::bzip2> has been upgraded from version 2.069 to 2.074. =item * L<:raw::zlib> has been upgraded from version 2.069 to 2.074. =item * L<:perl::v> has been upgraded from version 0.25 to 0.28. =item * L has been upgraded from version 2.11 to 2.18. =item * L<:meta> has been upgraded from version 2.150005 to 2.150010. =item * L<:dumper> has been upgraded from version 2.160 to 2.167. The XS implementation now supports Deparse. =item * L has been upgraded from version 1.835 to 1.840. =item * L<:peek> has been upgraded from version 1.23 to 1.26. =item * L<:ppport> has been upgraded from version 3.32 to 3.35. =item * L<:selfstubber> has been upgraded from version 1.05 to 1.06. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 1.34 to 1.36. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 1.17 to 1.17_01. =item * L<:md5> has been upgraded from version 2.54 to 2.55. =item * L<:sha> has been upgraded from version 5.95 to 5.96. =item * L has been upgraded from version 1.38 to 1.42. =item * L has been upgraded from version 2.80 to 2.88. =item * L has been upgraded from version 2.17 to 2.19. This module's default mode is no longer supported. It now dies when imported, unless the C option is being used. =item * L<:warnings> has been upgraded from version 0.12 to 0.13. This module is no longer supported. It emits a warning to that effect and then does nothing. =item * L has been upgraded from version 1.25 to 1.28. It now documents that using C automatically loads Errno for you. It now uses 3-arg C instead of 2-arg C. L =item * L<:embed> has been upgraded from version 1.33 to 1.34. It now uses 3-arg C instead of 2-arg C. L =item * L<:makemaker> has been upgraded from version 7.10_01 to 7.24. =item * L<:miniperl> has been upgraded from version 1.05 to 1.06. =item * L<:parsexs> has been upgraded from version 3.31 to 3.34. =item * L<:typemaps> has been upgraded from version 3.31 to 3.34. =item * L has been upgraded from version 1.42 to 1.47. =item * L<:copy> has been upgraded from version 2.31 to 2.32. =item * L<:fetch> has been upgraded from version 0.48 to 0.52. =item * L<:glob> has been upgraded from version 1.26 to 1.28. It now Issues a deprecation message for C<:glob::glob>. =item * L<:spec> has been upgraded from version 3.63 to 3.67. =item * L has been upgraded from version 2.02 to 2.03. =item * L<:simple> has been upgraded from version 0.92 to 0.93. It no longer treats C immediately following C as end-of-file. L =item * L<:long> has been upgraded from version 2.48 to 2.49. =item * L<:std> has been upgraded from version 1.11 to 1.12. =item * L<:util> has been upgraded from version 0.19 to 0.22. =item * L<:tiny> has been upgraded from version 0.056 to 0.070. Internal 599-series errors now include the redirect history. =item * L<:langtags> has been upgraded from version 0.40 to 0.42. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 1.36 to 1.38. =item * L<:socket::ip> has been upgraded from version 0.37 to 0.38. =item * L<:cmd> has been upgraded from version 0.92 to 0.96. =item * L<:sysv> has been upgraded from version 2.06_01 to 2.07. =item * L<:pp> has been upgraded from version 2.27300 to 2.27400_02. =item * L has been upgraded from version 0.63 to 0.64. It now uses 3-arg C instead of 2-arg C. L =item * L<:util> has been upgraded from version 1.42_02 to 1.46_02. =item * L<:codes> has been upgraded from version 3.37 to 3.42. =item * L<:maketext> has been upgraded from version 1.26 to 1.28. =item * L<:maketext::simple> has been upgraded from version 0.21 to 0.21_01. =item * L<:bigint> has been upgraded from version 1.999715 to 1.999806. =item * L<:bigint::fastcalc> has been upgraded from version 0.40 to 0.5005. =item * L<:bigrat> has been upgraded from version 0.260802 to 0.2611. =item * L<:complex> has been upgraded from version 1.59 to 1.5901. =item * L has been upgraded from version 1.03 to 1.03_01. =item * L<:corelist> has been upgraded from version 5.20170420 to 5.20170530. =item * L<:load::conditional> has been upgraded from version 0.64 to 0.68. =item * L<:metadata> has been upgraded from version 1.000031 to 1.000033. =item * L has been upgraded from version 1.18 to 1.20. =item * L<:ping> has been upgraded from version 2.43 to 2.55. IPv6 addresses and C sockets are now supported, along with several other enhancements. =item * L has been upgraded from version 0.65 to 0.67. =item * L has been upgraded from version 1.34 to 1.39. =item * L has been upgraded from version 1.10 to 1.11. =item * L<:process> has been upgraded from version 1.11 to 1.12. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 1.26 to 1.28. Its compilation speed has been improved slightly. =item * L has been upgraded from version 0.234 to 0.236. =item * L has been upgraded from version 1.50 to 1.51. It now ignores F on non-Unix systems. L =item * L<:ostype> has been upgraded from version 1.009 to 1.010. =item * L has been upgraded from version 5.021010 to 5.021011. =item * L has been upgraded from version 1.09 to 1.10. =item * L<:encoding> has been upgraded from version 0.24 to 0.25. =item * L<:scalar> has been upgraded from version 0.24 to 0.26. =item * L<:checker> has been upgraded from version 1.60 to 1.73. =item * L<:functions> has been upgraded from version 1.10 to 1.11. =item * L<:html> has been upgraded from version 1.22 to 1.2202. =item * L<:perldoc> has been upgraded from version 3.25_02 to 3.28. =item * L<:simple> has been upgraded from version 3.32 to 3.35. =item * L<:usage> has been upgraded from version 1.68 to 1.69. =item * L has been upgraded from version 1.65 to 1.76. This remedies several defects in making its symbols exportable. L The C<:tmpnam> interface has been removed, see L"POSIX::tmpnam() has been removed">. The following deprecated functions have been removed: POSIX::isalnum POSIX::isalpha POSIX::iscntrl POSIX::isdigit POSIX::isgraph POSIX::islower POSIX::isprint POSIX::ispunct POSIX::isspace POSIX::isupper POSIX::isxdigit POSIX::tolower POSIX::toupper Trying to import POSIX subs that have no real implementations (like C<:atend>) now fails at import time, instead of waiting until runtime. =item * L has been upgraded from version 0.32 to 0.34 This adds support for the new Lxx>|perlre/Ex and Exx> regular expression pattern modifier, and a change to the L>|re/'strict' mode> experimental feature. When S> is enabled, a warning now will be generated for all unescaped uses of the two characters C and C in regular expression patterns (outside bracketed character classes) that are taken literally. This brings them more in line with the C character which is always a metacharacter unless escaped. Being a metacharacter only sometimes, depending on an action at a distance, can lead to silently having the pattern mean something quite different than was intended, which the S> mode is intended to minimize. =item * L has been upgraded from version 2.39 to 2.40. =item * L<:util> has been upgraded from version 1.42_02 to 1.46_02. =item * L has been upgraded from version 2.56 to 2.62. Fixes L. =item * L has been upgraded from version 1.07 to 1.08. =item * L<:syslog> has been upgraded from version 0.33 to 0.35. =item * L<:ansicolor> has been upgraded from version 4.04 to 4.06. =item * L<:readline> has been upgraded from version 1.15 to 1.16. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 1.28 to 1.30. It now uses 3-arg C instead of 2-arg C. L =item * L<:harness> has been upgraded from version 3.36 to 3.38. =item * L<:simple> has been upgraded from version 1.001014 to 1.302073. =item * L<:queue> has been upgraded from version 3.09 to 3.12. =item * L<:semaphore> has been upgraded from 2.12 to 2.13. Added the C method. =item * L has been upgraded from version 2.07 to 2.15. =item * L<:shared> has been upgraded from version 1.51 to 1.56. =item * L<:hash::namedcapture> has been upgraded from version 0.09 to 0.10. =item * L<:hires> has been upgraded from version 1.9733 to 1.9741. It now builds on systems with C++11 compilers (such as G++ 6 and Clang++ 3.9). Now uses C. =item * L<:local> has been upgraded from version 1.2300 to 1.25. =item * L<:collate> has been upgraded from version 1.14 to 1.19. =item * L<:ucd> has been upgraded from version 0.64 to 0.68. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 0.9916 to 0.9917. =item * L<:dclsym> has been upgraded from version 1.06 to 1.08. It now uses 3-arg C instead of 2-arg C. L =item * L has been upgraded from version 1.36 to 1.37. =item * L<:typemap> has been upgraded from version 0.14 to 0.15. =item * L has been upgraded from version 0.21 to 0.27. Fixed a security hole in which binary files could be loaded from a path outside of L|perlvar/@INC>. It now uses 3-arg C instead of 2-arg C