/ 
FFI-C-0.15
River stage two • 11 direct dependents • 25 total dependents
/ FFI::C::File

NAME

FFI::C::File - Perl interface to C File pointer

VERSION

version 0.15

SYNOPSIS

use FFI::C::File;

my $file1 = FFI::C::File->fopen("foo.txt", "w");
my $content1 = "hello world!\n";
$file1->fwrite(\$content1, length $content);
$file1->fclose;

my $file2 = FFI::C::File->fopen("foo.txt", "r");
# take gets the file pointer, $file2 is no longer
# usable.
my $ptr = $file2->take;

# reconstitute the File object using the same file
# pointer
my $file3 = FFI::C::File->new($ptr);
my $content3 = "\0" x length $content;
$file3->fread(\$content3, length $content);
print $content3;  # "hello world!\n";

DESCRIPTION

This class provides an interface to the standard C library file pointers. Normally from Perl you want to use the native Perl file interfaces, but sometimes you might be working with a C library that uses C library file pointers (anytime you see the FILE* type this is the case), and having C native interface can be useful.

For example, if you have a C function that takes a file pointer:

void foo(FILE *fp);

You can use it from your Perl code like so:

use FFI::Platypus 1.00;
use FFI::C::File;

my $ffi = FFI::Platypus->new( api => 1 );
$ffi->attach( foo => ['object(FFI::C::File)'] );

my $file = FFI::C::File->fopen("foo.txt", "r");
foo($file);

As long as this class "owns" the file pointer it will close it automatically when it falls out of scope. If the C API you are calling is taking ownership of the file pointer and is expected to close the file itself, then you can use the take method to take the file pointer. Once this method is called, the file object is no longer usable (though it can be later reconstituted using the new constructor).

use FFI::Platypus 1.00;
use FFI::C::File;

my $ffi = FFI::Platypus->new( api => 1 );
$ffi->attach( foo => ['opaque'] );

my $file = FFI::C::File->fopen("foo.txt", "r");
my $ptr = $file->ptr;
foo($ptr);

Likewise, if a C API returns a file pointer that you are expected to close you can create a new File object from the opaque pointer using the new constructor. C:

FILE *bar();

Perl:

use FFI::Platypus 1.00;
use FFI::C::File;

my $ffi = FFI::Platypus->new( api => 1 );
$ffi->attach( bar => [] => 'opaque' );

my $ptr = bar();
my $file = FFI::C::File->new($ptr);
# can now read/write etc to/from $file

Constructors and methods will throw an exception on errors. End-of-File (EOF) is not considered an error.

The subclass FFI::C::PosixFile extends this class by adding some POSIX extensions for platforms that support them.

CONSTRUCTOR

fopen

my $file = FFI::C::File->fopen($filename, $mode);

Opens the file with the given mode. See your standard library C documentation for the exact format of $mode.

tmpfile

my $file = FFI::C::File->tmpfile;

Creates and opens a temporary file. The file is opened as binary file for update. On Windows this may require administrator privileges.

new

my $file = FFI::C::File->new($ptr);

Create a new File instance object from the opaque pointer. Note that it isn't possible to do any error checking on the type, so make sure that the pointer you are providing really is a C file pointer.

METHODS

freopen

$file->freopen($filename, $mode);

Re-open the file stream. If $filename is undef, then the same file is reopened. This can be useful for reopening a file in a different mode. Note that the mode changes that are allowed are platform dependent.

On some platforms (Linux, macOS and possibly some others) you can pass undef as the $filename. This is a way to change the $mode without changing the file.

fread

my $bytes = $file->fread(\$buffer, $size);

Read up to $size bytes into $buffer. $buffer must be preallocated, otherwise memory corruption will happen. Returns the number of bytes actually read, which may be fewer than the number of bytes requested if the end of file is reached.

fwrite

my $bytes = $file->fwrite(\$buffer, $size);

Write up to $size bytes from $buffer. Returns the number of bytes actually written.

fseek

$file->fseek($offset, $whence);

Seek to the specified location in the file. $whence should be one of the following (either strings, or constants can be used, the constants can be imported from this module):

'set' | SEEK_SET

Relative to the start of the file

'cur' | SEEK_CUR

Relative to the current location of the file pointer.

'end' | SEEK_END

Relative to the end of the file.

ftell

my $offset = $file->ftell;

Returns the file position indicator for the file pointer.

rewind

$file->rewind;

Moves the file position indicator to the beginning of the file.

fflush

$file->fflush;

Flush the file stream.

clearerr

$file->clearerr;

Clear the error flag for the file stream.

feof

my $bool = $file->feof;

Returns true if the end of file has been reached. False otherwise.

ferror

my $error = $file->ferror;

Returns the file error code.

take

my $ptr = $file->take;

Takes ownership of the file from the object and returns the opaque file pointer.

fclose

$file->close;

Close the file.

SEE ALSO

FFI::C
FFI::C::Array
FFI::C::ArrayDef
FFI::C::Def
FFI::C::File
FFI::C::PosixFile
FFI::C::Struct
FFI::C::StructDef
FFI::C::Union
FFI::C::UnionDef
FFI::C::Util
FFI::Platypus::Record

AUTHOR

Graham Ollis <plicease@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2020-2022 by Graham Ollis.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.