perl如何调用其它编程语言（如C）

Question

问题描述:
unix环境下，在perl中
1、如何调用一个标准C函数。
2、如何调用一个4gl编写的函数。
3、如何调用一个操作系统函数或系统调用。

操作系统环境：
linux

具体测试代码和例子：

Makefile.PL内容如下：
代码:

2. use ExtUtils::MakeMaker;
3. # See lib/ExtUtils/MakeMaker.pm for details of how to influence
4. # the contents of the Makefile that is written.
5. WriteMakefile(
6.     'NAME'              =>; 'Mytest',
7.     'VERSION_FROM'      =>; 'Mytest.pm', # finds $VERSION
8.     'PREREQ_PM'         =>; {}, # e.g., Module::Name =>; 1.1
9.     'LIBS'              =>; [''], # e.g., '-lm'
10.     'DEFINE'            =>; '', # e.g., '-DHAVE_SOMETHING'
11.     'INC'               =>; '', # e.g., '-I/usr/include/other'
12. );

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Mytest.PM的内容如下：
代码:

2. package Mytest;
4. require 5.005_62;
5. use strict;
6. use warnings;
8. require Exporter;
9. require DynaLoader;
11. our @ISA = qw(Exporter DynaLoader);
13. # Items to export into callers namespace by default. Note: do not export
14. # names by default without a very good reason. Use EXPORT_OK instead.
15. # Do not simply export all your public functions/methods/constants.
17. # This allows declaration       use Mytest ':all';
18. # If you do not need this, moving things directly into @EXPORT or @EXPORT_OK
19. # will save memory.
20. our %EXPORT_TAGS = ( 'all' =>; [ qw(
22. ) ] );
24. our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
25. our @EXPORT = qw(
27. );
28. our $VERSION = '0.01';
30. bootstrap Mytest $VERSION;
32. # Preloaded methods go here.
34. 1;
35. __END__
36. # Below is stub documentation for your module. You better edit it!
38. =head1 NAME
40. Mytest - Perl extension for blah blah blah
42. =head1 SYNOPSIS
44.   use Mytest;
45.   blah blah blah
46. =head1 DESCRIPTION
48. Stub documentation for Mytest, created by h2xs. It looks like the
49. author of the extension was negligent enough to leave the stub
50. unedited.
52. Blah blah blah.
54. =head2 EXPORT
56. None by default.
59. =head1 AUTHOR
61. A. U. Thor, a.u.thor@a.galaxy.far.far.away
63. =head1 SEE ALSO
65. perl(1).
67. =cut

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Mytest.xs内容如下：

代码:

2. #include "EXTERN.h"
3. #include "perl.h"
4. #include "XSUB.h"
6. MODULE = Mytest         PACKAGE = Mytest

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上面这个是大体的框架，我现在自己写了一个c函数，例如：
代码:

2. #include <stdio.h>;
4. static int testfun( int );
6. int main( void )
7. {
8.     (void)fprintf(stderr,"Sample for test.\n");
9.     if( testfun( 100 ) < 0 ) {
10.         (void)fprintf(stderr,"testfun error!\n");
11.         exit(-1);
12.     }
13.     exit(0);
14. }
16. int testfun(int num )
17. {
18.     if( num >; 0 )
19.         printf("Int num = %d\n", num );
20.     else
21.         return -1;
22.     return 0;
23. }

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需求：
现在如何在上面那几个文件中添加，让perl可以执行c的函数。
如果使用其它的方式，怎么使用，具体的例子是什么