I have produced a number of tests below which walk through my findings of the ftruncate function. For the impatient among you ftruncate can be used to increase the size of the file and will fill the rest of the file with CHR 0 or ASCII NULL. It can be used as a very convenient way of making a 1Mb file for instance.
Test 1
<?php
/*
Test 1: Write "some text" to a file.
Result: The text "some text" should be present in test_1.txt
*/
$fp = fopen('test_1.txt', 'w+');
fwrite($fp, 'some text');
?>
The first test is only here to make sure that a file can be written with some text.
Test 2
<?php
/*
Test 2: Write "some text" to a file and ftruncate the file to 4 bytes.
Result: The text "some" should be present in test_2.txt as the file will have been truncated to 4 bytes.
*/
$fp = fopen('test_2.txt', 'w+');
fwrite($fp, 'some text');
ftruncate($fp, 4);
?>
As expected the file has been truncated to 4 bytes.
Test 3
<?php
/*
Test 3: Write "some text" to a file and ftruncate the file to 40 bytes.
Result: The text "some text" should be present in test_3.txt as the file will have been truncated to 40 bytes.
*/
$fp = fopen('test_3.txt', 'w+');
fwrite($fp, 'some text');
ftruncate($fp, 40);
?>
Interestingly the file has increased from 9 bytes to 40 bytes. The remaining 31 bytes of the file are ASCII code 0 or NULL though.
Further notes can be found here http://mikeleigh.com/links/ftruncate
ftruncate
(PHP 4, PHP 5)
ftruncate — ファイルを指定した長さに丸める
説明
bool ftruncate ( resource $handle, int $size )ファイルポインタhandleを引数とし、 ファイルを指定した長さ、サイズに丸めます。 成功した場合に TRUE を、失敗した場合に FALSE を返します。
注意: ファイルポインタは 追加 モードの時のみ変更されます。 書き込み モードの場合、 fseek() を追加でコールする必要があります。
注意: PHP 4.3.3未満では、 ftruncate() は成功の場合に booleanの TRUE ではなく integerの 1 を返します。
ftruncate
mike at mikeleigh dot com
04-Jan-2007 05:30
04-Jan-2007 05:30