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(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

shmop_writeWrite data into shared memory block


shmop_write(Shmop $shmop, string $data, int $offset): int

shmop_write() will write a string into shared memory block.



The shared memory block identifier created by shmop_open()


A string to write into shared memory block


Specifies where to start writing data inside the shared memory segment. The offset must be greater than or equal to zero and less than or equal to the actual size of the shared memory segment.

Return Values

The size of the written data.


If offset is out of range, or a read-only shared memory segment should be written to, a ValueError is thrown.


Version Description
8.0.0 Prior to PHP 8.0.0, false was returned on failure.
8.0.0 shmop expects a Shmop instance now; previously, a resource was expected.


Example #1 Writing to shared memory block

= shmop_write($shm_id, $my_string, 0);

This example will write data inside $my_string into shared memory block, $shm_bytes_written will contain the number of bytes written.

See Also

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User Contributed Notes 2 notes

mark at manngo dot net
1 year ago
On thing you might want to do is replace an old string with a shorter one, or to clear out the string altogether.

To replace the string, you can zero-byte pad the string you are writing:

// $shmid is from shmop_open()
$size = 128;
$string = 'something';

// write
$string = str_pad(string, $size, "\0");
shmop_write($shmid, $string, 0);

// read
print rtrim(shmop($shmid,0,0),,"\0");

// clear
$string = str_repeat("\0",$size);
shmop_write($shmid, $string, 0);
radupb at yahoo dot com
3 years ago
I guess pack-unpack are the handy functions for encoding/decoding data as/from a binary string for shmop_write/shmop_read. Example:

$format='LLLLSSCCCC'; //data format for pack
if( !($shmid=shmop_open($key,'n',0660,30)) )
die('shmop_open failed.');

//my data to encode:

$tmp=pack( $format, $hd['ALIVE1'],$hd['ALIVE2'],$hd['ALIVE3'],$hd['ALIVE4'], $hd['CRTPTR'],$hd['CRTSEQ'],$hd['CTW'],$hd['LOCK'],$hd['PLAY'],$hd['MISS'] );

if( ($w=shmop_write($shmid,$tmp,0))!=24 )
die('write error $w='.$w);

And reading from some other process:
if( !($shmid=shmop_open($key,'w',0,0)) )
die('shmop_open failed.');

$formatR='L4ALIVE/SCRTPTR/SCRTSEQ/CCTW/CLOCK/CPLAY/CMISS'; //data format for unpack

$hd=unpack( $formatR, shmop_read( $shmid,0,24) );
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