FFI::Platypus::Type::StringPointer3pm

In your C code:

 void
 string_pointer_argument(const char **string)
 {
   ...
 }
 const char **
 string_pointer_return(void)
 {
   ...
 }

In your Platypus::FFI code:

 use FFI::Platypus 2.00;
 
 my $ffi = FFI::Platypus->new( api => 2 );
 $ffi->load_custom_type('::StringPointer' => 'string_pointer');
 
 $ffi->attach(string_pointer_argument => ['string_pointer'] => 'void');
 $ffi->attach(string_pointer_return   => [] => 'string_pointer');
 
 my $string = "foo";
 
 string_pointer_argument(\$string); # $string may be modified
 
 $ref = string_pointer_return();
 
 print $$ref;  # print the string pointed to by $ref