odbc_longreadlen()

(PHP 4, PHP 5, PHP 7)

Handling of LONG columns

说明

odbc_longreadlen(resource $result_id,int $length): bool

Enables handling of LONG and LONGVARBINARY columns.

参数

$result_id: The result identifier.
$length: The number of bytes returned to PHP is controlled by the parameter length. If it is set to 0, Long column data is passed through to the client.

返回值

成功时返回TRUE，或者在失败时返回FALSE。

注释

Note:
Handling of LONGVARBINARY columns is also affected by odbc_binmode().

Hi
If you are experiencing troubles with truncated and/or strangely encoded data when using PHP with MS SQL via ODBC try setting odbc.defaultlrl ( in php.ini or via ini_set() ) to a largish number, say 65536, as stated in the other notes here. 
The trick is to know how long your data is going to be, so you may want to provide some overhead. Unfortunately you have to know how long your piece of string is before you cut it.
Doing this will allow your app to read up to this amount in one go. I'm sure there is a reason for this behaviour but I hadn't experienced anything like it in 5 years of MySQL and Postgres development.
If you still experience problems AND are using unicode data in the long column of your table, make sure it is set to type "ntext", if it is "text". MSDN has some info on data types for Unicode data.
This caused about 3 days of headaches for me, "binary" data crashing browsers and cyclical result sets (i.e repeating data after odbc.defaultlrl bytes). 
This fix was only found by poking things with sticks.
HTH

I've tried to use a suggestion in the first comment but that didn't actually worked as I would expect... I wanted to get all data no matter how big it is, but strange things happened and I finally found this solution (works fine at least for MS SQL 2000 for at least few MB of binary data):
<?php
// connection
$link = odbc_connect($odbc_source_name, $user, $pass);
// query (note - one row in this example)
$sql = 'SELECT image_data_column FROM some_table WHERE record_id=1';
// run
$result = odbc_exec ($link, $sql)
if (!$result)
{
  trigger_error ('[sql] exec: '.$sql, E_USER_ERROR);
}
// fetch settings
odbc_binmode ($result, ODBC_BINMODE_PASSTHRU); 
odbc_longreadlen ($result, 0);
// get contents
ob_start(); // you would probably need to move this inside if you expect more rows
while (odbc_fetch_row($result))
{
  odbc_result($result, 1); // this actually echos all of the contents of the image_data_column
}
odbc_free_result($result);
$contents = ob_get_clean();
?>

It's not mentioned in the notes here, but odbc_longreadlen($result, 0); only affects the output from odbc_result(). Setting the read length to 0 (or less than zero) will just output a blank string in the odbc_fetch_object(), odbc_fetch_array() and odbc_result_all() functions

I was reading from a MEMO field (long varchar) in MSAccess, but the data was consistently truncated at 255 characters. I tried all the combinations of odbc_longreadlen() and odbc_binmode() (and odbc.defaultlrl) that I could think of but none of them resolved the problem.
The only fix that worked was to modify my query from "SELECT Field1, Field2 FROM TableName" to "SELECT * FROM TableName".
I suspect that you could cast the field to force the appropriate data type, but when it finally worked after three days of struggle I didn't even try.

An alternative is to adjust your php.ini file and set:
odbc.defaultlrl=65536
Or something else sufficiently large.
lrl = long read length

I had a heck of a time figuring out what to do with this function. Here's a little piece of code from Jason Lee which I found that might help someone else...
$cur = odbc_exec($cnx, $query); 
if(!$cur) { 
/* error handler */ 
} 
odbc_binmode($cur, ODBC_BINMODE_PASSTHRU); 
odbc_longreadlen($cur, 16384); /* Allow 16kb thru */ 
while(odbc_fetch_row($cur)) { 
$bigger_than_4096_var = odbc_result($cur, 1); 
/* etc... */ 
Hope this helps someone, John

Aaargh!
I was wondering about truncated data when reading from a TEXT (LONG VARCHAR) column.
With this I was able to increase the buffer size...