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ExtUtils::CChecker.3pm

NAME

"ExtUtils::CChecker" - configure-time utilities for using C headers, libraries, or OS features

SYNOPSIS

  use Module::Build;
  use ExtUtils::CChecker;
 
  my $check_PF_MOONLASER = <<'EOF';
  #include <stdio.h>
  #include <sys/socket.h>
  int main(int argc, char *argv[]) {
    printf("PF_MOONLASER is %d\n", PF_MOONLASER);
    return 0;
  }
  EOF
 
  ExtUtils::CChecker->new->assert_compile_run(
     diag => "no PF_MOONLASER",
     source => $check_PF_MOONLASER,
  );
 
  Module::Build->new(
    ...
  )->create_build_script;
 
 

DESCRIPTION

Often Perl modules are written to wrap functionallity found in existing C headers, libraries, or to use OS-specific features. It is useful in the Build.PL or Makefile.PL file to check for the existance of these requirements before attempting to actually build the module.

Objects in this class provide an extension around ExtUtils::CBuilder to simplify the creation of a .c file, compiling, linking and running it, to test if a certain feature is present.

It may also be necessary to search for the correct library to link against, or for the right include directories to find header files in. This class also provides assistance here.

CONSTRUCTOR

$cc = ExtUtils::CChecker->new

Returns a new instance of a "ExtUtils::CChecker" object.

METHODS

$dirs = $cc->include_dirs

Returns the currently-configured include directories in an ARRAY reference.

$flags = $cc->extra_compiler_flags

Returns the currently-configured extra compiler flags in an ARRAY reference.

$flags = $cc->extra_linker_flags

Returns the currently-configured extra linker flags in an ARRAY reference.

$success = $cc->try_compile_run( %args )

$success = $cc->try_compile_run( $source )

Try to compile, link, and execute a C program whose source is given. Returns true if the program compiled and linked, and exited successfully. Returns false if any of these steps fail.

Takes the following named arguments. If a single argument is given, that is taken as the source string.

*

source => STRING

The source code of the C program to try compiling, building, and running.

*

extra_compiler_flags => ARRAY

Optional. If specified, pass extra flags to the compiler.

*

extra_linker_flags => ARRAY

Optional. If specified, pass extra flags to the linker.

*

define => STRING

Optional. If specified, then the named symbol will be defined on the C compiler commandline if the program ran successfully (by passing an option "-DSYMBOL").

$cc->assert_compile_run( %args )

Calls "try_compile_run". If it fails, die with an "OS unsupported" message. Useful to call from Build.PL or Makefile.PL.

Takes one extra optional argument:

*

diag => STRING

If present, this string will be appended to the failure message if one is generated. It may provide more useful information to the user on why the OS is unsupported.

$success = $cc->try_find_include_dirs_for( %args )

Try to compile, link and execute the given source, using extra include directories.

When a usable combination is found, the directories required are stored in the object for use in further compile operations, or returned by "include_dirs". The method then returns true.

If no a usable combination is found, it returns false.

Takes the following arguments:

*

source => STRING

Source code to compile

*

dirs => ARRAY of ARRAYs

Gives a list of sets of dirs. Each set of dirs should be strings in its own array reference.

*

define => STRING

Optional. If specified, then the named symbol will be defined on the C compiler commandline if the program ran successfully (by passing an option "-DSYMBOL").

$success = $cc->try_find_libs_for( %args )

Try to compile, link and execute the given source, when linked against a given set of extra libraries.

When a usable combination is found, the libraries required are stored in the object for use in further link operations, or returned by "extra_linker_flags". The method then returns true.

If no usable combination is found, it returns false.

Takes the following arguments:

*

source => STRING

Source code to compile

*

libs => ARRAY of STRINGs

Gives a list of sets of libraries. Each set of libraries should be space-separated.

*

define => STRING

Optional. If specified, then the named symbol will be defined on the C compiler commandline if the program ran successfully (by passing an option "-DSYMBOL").

$cc->find_include_dirs_for( %args )

$cc->find_libs_for( %args )

Calls "try_find_include_dirs_for" or "try_find_libs_for" respectively. If it fails, die with an "OS unsupported" message.

Each method takes one extra optional argument:

*

diag => STRING

If present, this string will be appended to the failure message if one is generated. It may provide more useful information to the user on why the OS is unsupported.

$mb = $cc->new_module_build( %args )

Construct and return a new Module::Build object, preconfigured with the "include_dirs", "extra_compiler_flags" and "extra_linker_flags" options that have been configured on this object, by the above methods.

This is provided as a simple shortcut for the common use case, that a Build.PL file is using the "ExtUtils::CChecker" object to detect the required arguments to pass.

EXAMPLES

Socket Libraries

Some operating systems provide the BSD sockets API in their primary libc. Others keep it in a separate library which should be linked against. The following example demonstrates how this would be handled.

  use Module::Build;
  use ExtUtils::CChecker;
 
  my $cc = ExtUtils::CChecker->new;
 
  $cc->find_libs_for(
     diag => "no socket()",
     libs => [ "", "socket nsl" ],
     source => q[
  #include <sys/socket.h>
  int main(int argc, char *argv) {
    int fd = socket(PF_INET, SOCK_STREAM, 0);
    if(fd < 0)
      return 1;
    return 0;
  }
  ] );
 
  $cc->new_module_build(
     module_name => "Your::Name::Here",
     requires => {
        'IO::Socket' => 0,
     },
     ...
  )->create_build_script;
 
 

By using the "new_module_build" method, the detected "extra_linker_flags" value has been automatically passed into the new "Module::Build" object.

Testing For Optional Features

Sometimes a function or ability may be optionally provided by the OS, or you may wish your module to be useable when only partial support is provided, without requiring it all to be present. In these cases it is traditional to detect the presence of this optional feature in the Build.PL script, and define a symbol to declare this fact if it is found. The XS code can then use this symbol to select between differing implementations. For example, the Build.PL:

  use Module::Build;
  use ExtUtils::CChecker;
 
  my $cc = ExtUtils::CChecker->new;
 
  $cc->try_compile_run(
     define => "HAVE_MANGO",
     source => <<'EOF' );
  #include <mango.h>
  #include <unistd.h>
  int main(void) {
    if(mango() != 0)
      exit(1);
    exit(0);
  }
  EOF
 
  $cc->new_module_build(
     ...
  )->create_build_script;
 
 

If the C code compiles and runs successfully, and exits with a true status, the symbol "HAVE_MANGO" will be defined on the compiler commandline. This allows the XS code to detect it, for example

  int
  mango()
    CODE:
  #ifdef HAVE_MANGO
      RETVAL = mango();
  #else
      croak("mango() not implemented");
  #endif
    OUTPUT:
      RETVAL
 
 

This module will then still compile even if the operating system lacks this particular function. Trying to invoke the function at runtime will simply throw an exception.

Linux Kernel Headers

Operating systems built on top of the Linux kernel often share a looser association with their kernel version than most other operating systems. It may be the case that the running kernel is newer, containing more features, than the distribution's libc headers would believe. In such circumstances it can be difficult to make use of new socket options, "ioctl()"s, etc.. without having the constants that define them and their parameter structures, because the relevant header files are not visible to the compiler. In this case, there may be little choice but to pull in some of the kernel header files, which will provide the required constants and structures.

The Linux kernel headers can be found using the /lib/modules directory. A fragment in Build.PL like the following, may be appropriate.

  chomp( my $uname_r = `uname -r` );
 
  my @dirs = (
     [],
     [ "/lib/modules/$uname_r/source/include" ],
  );
 
  $cc->find_include_dirs_for(
     diag => "no PF_MOONLASER",
     dirs => \@dirs,
     source => <<'EOF' );
  #include <sys/socket.h>
  #include <moon/laser.h>
  int family = PF_MOONLASER;
  struct laserwl lwl;
  int main(int argc, char *argv[]) {
    return 0;
  }
  EOF
 
 

This fragment will first try to compile the program as it stands, hoping that the libc headers will be sufficient. If it fails, it will then try including the kernel headers, which should make the constant and structure visible, allowing the program to compile.

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>