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Gurusamy Sarathy


h2xs - convert .h C header files to Perl extensions


h2xs [-ACOPXcdf] [-v version] [-n module_name] [-p prefix] [-s sub] [headerfile ... [extra_libraries]]

h2xs -h


h2xs builds a Perl extension from C header files. The extension will include functions which can be used to retrieve the value of any #define statement which was in the C header files.

The module_name will be used for the name of the extension. If module_name is not supplied then the name of the first header file will be used, with the first character capitalized.

If the extension might need extra libraries, they should be included here. The extension Makefile.PL will take care of checking whether the libraries actually exist and how they should be loaded. The extra libraries should be specified in the form -lm -lposix, etc, just as on the cc command line. By default, the Makefile.PL will search through the library path determined by Configure. That path can be augmented by including arguments of the form -L/another/library/path in the extra-libraries argument.



Omit all autoload facilities. This is the same as -c but also removes the use AutoLoader statement from the .pm file.


Omits creation of the Changes file, and adds a HISTORY section to the POD template.


Additional flags to specify to C preprocessor when scanning header for function declarations. Should not be used without -x.


Allows a pre-existing extension directory to be overwritten.


Omit the autogenerated stub POD section.


Omit the XS portion. Used to generate templates for a module which is not XS-based. -c and -f are implicitly enabled.


Omit constant() from the .xs file and corresponding specialised AUTOLOAD from the .pm file.


Turn on debugging messages.


Allows an extension to be created for a header even if that header is not found in /usr/include.


Print the usage, help and version for this h2xs and exit.

-n module_name

Specifies a name to be used for the extension, e.g., -n RPC::DCE

-p prefix

Specify a prefix which should be removed from the Perl function names, e.g., -p sec_rgy_ This sets up the XS PREFIX keyword and removes the prefix from functions that are autoloaded via the constant() mechanism.

-s sub1,sub2

Create a perl subroutine for the specified macros rather than autoload with the constant() subroutine. These macros are assumed to have a return type of char *, e.g., -s sec_rgy_wildcard_name,sec_rgy_wildcard_sid.

-v version

Specify a version number for this extension. This version number is added to the templates. The default is 0.01.


Automatically generate XSUBs basing on function declarations in the header file. The package C::Scan should be installed. If this option is specified, the name of the header file may look like NAME1,NAME2. In this case NAME1 is used instead of the specified string, but XSUBs are emitted only for the declarations included from file NAME2.

Note that some types of arguments/return-values for functions may result in XSUB-declarations/typemap-entries which need hand-editing. Such may be objects which cannot be converted from/to a pointer (like long long), pointers to functions, or arrays.


        # Default behavior, extension is Rusers
        h2xs rpcsvc/rusers

        # Same, but extension is RUSERS
        h2xs -n RUSERS rpcsvc/rusers

        # Extension is rpcsvc::rusers. Still finds <rpcsvc/rusers.h>
        h2xs rpcsvc::rusers

        # Extension is ONC::RPC.  Still finds <rpcsvc/rusers.h>
        h2xs -n ONC::RPC rpcsvc/rusers

        # Without constant() or AUTOLOAD
        h2xs -c rpcsvc/rusers

        # Creates templates for an extension named RPC
        h2xs -cfn RPC

        # Extension is ONC::RPC.
        h2xs -cfn ONC::RPC

        # Makefile.PL will look for library -lrpc in 
        # additional directory /opt/net/lib
        h2xs rpcsvc/rusers -L/opt/net/lib -lrpc

        # Extension is DCE::rgynbase
        # prefix "sec_rgy_" is dropped from perl function names
        h2xs -n DCE::rgynbase -p sec_rgy_ dce/rgynbase

        # Extension is DCE::rgynbase
        # prefix "sec_rgy_" is dropped from perl function names
        # subroutines are created for sec_rgy_wildcard_name and sec_rgy_wildcard_sid
        h2xs -n DCE::rgynbase -p sec_rgy_ \
        -s sec_rgy_wildcard_name,sec_rgy_wildcard_sid dce/rgynbase

        # Make XS without defines in perl.h, but with function declarations
        # visible from perl.h. Name of the extension is perl1.
        # When scanning perl.h, define -DEXT=extern -DdEXT= -DINIT(x)=
        # Extra backslashes below because the string is passed to shell.
        # Note that a directory with perl header files would 
        #  be added automatically to include path.
        h2xs -xAn perl1 -F "-DEXT=extern -DdEXT= -DINIT\(x\)=" perl.h

        # Same with function declaration in proto.h as visible from perl.h.
        h2xs -xAn perl2 perl.h,proto.h


No environment variables are used.


Larry Wall and others


perl, perlxstut, ExtUtils::MakeMaker, and AutoLoader.


The usual warnings if it cannot read or write the files involved.



Original version; created by h2xs $H2XS_VERSION


my $const_doc = ''; my $fdecl_doc = ''; if (@const_names and not $opt_P) { $const_doc = <<EOD; \n=head2 Exported constants

  @{[join "\n  ", @const_names]}

EOD } if (defined $fdecls and @$fdecls and not $opt_P) { $fdecl_doc = <<EOD; \n=head2 Exported functions

  @{[join "\n  ", @$fdecls]}


$pod = <<"END" unless $opt_P; ## Below is the stub of documentation for your module. You better edit it! # #=head1 NAME # #$module - Perl extension for blah blah blah # #=head1 SYNOPSIS # # use $module; # blah blah blah # #=head1 DESCRIPTION # #Stub documentation for $module was created by h2xs. It looks like the #author of the extension was negligent enough to leave the stub #unedited. # #Blah blah blah. #$const_doc$fdecl_doc$revhist #=head1 AUTHOR # #$author, $email # #=head1 SEE ALSO # #perl(1). # #=cut END

$pod =~ s/^\#//gm unless $opt_P; print PM $pod unless $opt_P;

close PM;

if( ! $opt_X ){ # print XS, unless it is disabled warn "Writing $ext$modpname/$modfname.xs\n";

print XS <<"END"; #include "EXTERN.h" #include "perl.h" #include "XSUB.h"

END if( @path_h ){ foreach my $path_h (@path_h) { my($h) = $path_h; $h =~ s#^/usr/include/##; if ($^O eq 'VMS') { $h =~ s#.*vms\]#sys/# or $h =~ s#.*[:>\]]##; } print XS qq{#include <$h>\n}; } print XS "\n"; }

if( ! $opt_c ){ print XS <<"END"; static int not_here(char *s) { croak("$module::%s not implemented on this architecture", s); return -1; }

static double constant(char *name, int arg) { errno = 0; switch (*name) { END

my(@AZ, @az, @under);

foreach(@const_names){ @AZ = 'A' .. 'Z' if !@AZ && /^[A-Z]/; @az = 'a' .. 'z' if !@az && /^[a-z]/; @under = '_' if !@under && /^_/; }

foreach $letter (@AZ, @az, @under) {

    last if $letter eq 'a' && !@const_names;

    print XS "    case '$letter':\n";
    while (substr($const_names[0],0,1) eq $letter) {
        $name = shift(@const_names);
        $macro = $prefix{$name} ? "$opt_p$name" : $name;
        next if $const_xsub{$macro};
        print XS <<"END";
        if (strEQ(name, "$name"))
#ifdef $macro
            return $macro;
            goto not_there;
    print XS <<"END";
print XS <<"END";
    errno = EINVAL;
    return 0;

not_there: errno = ENOENT; return 0; }


$prefix = "PREFIX = $opt_p" if defined $opt_p; # Now switch from C to XS by issuing the first MODULE declaration: print XS <<"END";

MODULE = $module PACKAGE = $module $prefix


foreach (sort keys %const_xsub) { print XS <<"END"; char * $_()

#ifdef $_
    RETVAL = $_;
    croak("Your vendor has not defined the $module macro $_");



# If a constant() function was written then output a corresponding # XS declaration: print XS <<"END" unless $opt_c;

double constant(name,arg) char * name int arg


my %seen_decl;

sub print_decl { my $fh = shift; my $decl = shift; my ($type, $name, $args) = @$decl; return if $seen_decl{$name}++; # Need to do the same for docs as well?

  my @argnames = map {$_->[1]} @$args;
  my @argtypes = map { normalize_type( $_->[0] ) } @$args;
  my @argarrays = map { $_->[4] || '' } @$args;
  my $numargs = @$args;
  if ($numargs and $argtypes[-1] eq '...') {
    $argnames[-1] = '...';
  local $" = ', ';
  $type = normalize_type($type);
  print $fh <<"EOP";

$type $name(@argnames) EOP

  for $arg (0 .. $numargs - 1) {
    print $fh <<"EOP";
        $argtypes[$arg] $argnames[$arg]$argarrays[$arg]

# Should be called before any actual call to normalize_type(). sub get_typemap { # We do not want to read ./typemap by obvios reasons. my @tm = qw(../../../typemap ../../typemap ../typemap); my $stdtypemap = "$Config::Config{privlib}/ExtUtils/typemap"; unshift @tm, $stdtypemap; my $proto_re = "[" . quotemeta('\$%&*@;') . "]" ; my $image;

  foreach $typemap (@tm) {
    next unless -e $typemap ;
    # skip directories, binary files etc.
    warn " Scanning $typemap\n";
    warn("Warning: ignoring non-text typemap file '$typemap'\n"), next 
      unless -T $typemap ;
    open(TYPEMAP, $typemap) 
      or warn ("Warning: could not open typemap file '$typemap': $!\n"), next;
    my $mode = 'Typemap';
    while (<TYPEMAP>) {
      next if /^\s*\#/;
      if (/^INPUT\s*$/)   { $mode = 'Input'; next; }
      elsif (/^OUTPUT\s*$/)  { $mode = 'Output'; next; }
      elsif (/^TYPEMAP\s*$/) { $mode = 'Typemap'; next; }
      elsif ($mode eq 'Typemap') {
        next if /^\s*($|\#)/ ;
        if ( ($type, $image) = 
             # This may reference undefined functions:
             and not ($image eq 'T_PACKED' and $typemap eq $stdtypemap)) {
    close(TYPEMAP) or die "Cannot close $typemap: $!";
  %std_types = %types_seen;
  %types_seen = ();

sub normalize_type { my $ignore_mods = '(?:\b(?:__const__|static|inline|__inline__)\b\s*)*'; my $type = shift; $type =~ s/$ignore_mods//go; $type =~ s/([\]\[()])/ \1 /g; $type =~ s/\s+/ /g; $type =~ s/\s+$//; $type =~ s/^\s+//; $type =~ s/\b\*/ */g; $type =~ s/\*\b/* /g; $type =~ s/\*\s+(?=\*)/*/g; $types_seen{$type}++ unless $type eq '...' or $type eq 'void' or $std_types{$type}; $type; }

if ($opt_x) { for $decl (@$fdecls_parsed) { print_decl(\*XS, $decl) } }

close XS;

if (%types_seen) { my $type; warn "Writing $ext$modpname/typemap\n"; open TM, ">typemap" or die "Cannot open typemap file for write: $!";

  for $type (keys %types_seen) {
    print TM $type, "\t" x (6 - int((length $type)/8)), "T_PTROBJ\n"

  close TM or die "Cannot close typemap file for write: $!";

} # if( ! $opt_X )

warn "Writing $ext$modpname/Makefile.PL\n"; open(PL, ">Makefile.PL") || die "Can't create $ext$modpname/Makefile.PL: $!\n";

print PL <<'END'; use ExtUtils::MakeMaker; # See lib/ExtUtils/MakeMaker.pm for details of how to influence # the contents of the Makefile that is written. END print PL "WriteMakefile(\n"; print PL " 'NAME' => '$module',\n"; print PL " 'VERSION_FROM' => '$modfname.pm', # finds \$VERSION\n"; if( ! $opt_X ){ # print C stuff, unless XS is disabled print PL " 'LIBS' => ['$extralibs'], # e.g., '-lm' \n"; print PL " 'DEFINE' => '', # e.g., '-DHAVE_SOMETHING' \n"; print PL " 'INC' => '', # e.g., '-I/usr/include/other' \n"; } print PL ");\n"; close(PL) || die "Can't close $ext$modpname/Makefile.PL: $!\n";

warn "Writing $ext$modpname/test.pl\n"; open(EX, ">test.pl") || die "Can't create $ext$modpname/test.pl: $!\n"; print EX <<'_END_'; # Before `make install' is performed this script should be runnable with # `make test'. After `make install' it should work as `perl test.pl'

######################### We start with some black magic to print on failure.

# Change 1..1 below to 1..last_test_to_print . # (It may become useful if the test is moved to ./t subdirectory.)

BEGIN { $| = 1; print "1..1\n"; } END {print "not ok 1\n" unless $loaded;} _END_ print EX <<_END_; use $module; _END_ print EX <<'_END_'; $loaded = 1; print "ok 1\n";

######################### End of black magic.

# Insert your test code below (better if it prints "ok 13" # (correspondingly "not ok 13") depending on the success of chunk 13 # of the test code):

_END_ close(EX) || die "Can't close $ext$modpname/test.pl: $!\n";

unless ($opt_C) { warn "Writing $ext$modpname/Changes\n"; open(EX, ">Changes") || die "Can't create $ext$modpname/Changes: $!\n"; print EX "Revision history for Perl extension $module.\n\n"; print EX "$TEMPLATE_VERSION ",scalar localtime,"\n"; print EX "\t- original version; created by h2xs $H2XS_VERSION\n\n"; close(EX) || die "Can't close $ext$modpname/Changes: $!\n"; }

warn "Writing $ext$modpname/MANIFEST\n"; open(MANI,'>MANIFEST') or die "Can't create MANIFEST: $!"; @files = <*>; if (!@files) { eval {opendir(D,'.');}; unless ($@) { @files = readdir(D); closedir(D); } } if (!@files) { @files = map {chomp && $_} `ls`; } if ($^O eq 'VMS') { foreach (@files) { # Clip trailing '.' for portability -- non-VMS OSs don't expect it s%\.$%%; # Fix up for case-sensitive file systems s/$modfname/$modfname/i && next; $_ = "\U$_" if $_ eq 'manifest' or $_ eq 'changes'; $_ = 'Makefile.PL' if $_ eq 'makefile.pl'; } } print MANI join("\n",@files), "\n"; close MANI; !NO!SUBS!

close OUT or die "Can't close $file: $!"; chmod 0755, $file or die "Can't reset permissions for $file: $!\n"; exec("$Config{'eunicefix'} $file") if $Config{'eunicefix'} ne ':'; chdir $origdir;