PHP shmop_size() returns the capacity, in bytes, of a shared-memory block. The examples below show how the call behaves, where it is useful, and which limitations matter.
What Is shmop_size() in PHP?
Returns the capacity, in bytes, of a shared-memory block.
Its call structure is:
shmop_size($shmop)The arguments identify the values or resources passed to shmop_size(). Read the examples with attention to the type of each supplied argument and to whether the function modifies its input or returns a separate result.
Requires the corresponding System V shared-memory or SHMOP extension and suitable operating-system support. IPC keys used below are illustrative; use coordinated, environment-appropriate keys in real deployments.
Example 1: Basic Usage
This example introduces shmop_size with a direct call and a small, readable input.
<?php
$memory = shmop_open(0x34591, "n", 0600, 128);
if ($memory !== false) { echo shmop_size($memory); shmop_delete($memory); }Returns the capacity, in bytes, of a shared-memory block. Capacity is not the length of meaningful application content.
Example 2: Another Behavior or Input
Compare this input with the previous example: changing the data or option can affect how shmop_size behaves.
<?php
$memory = shmop_open(0x34592, "n", 0600, 256);
if ($memory !== false) { var_dump(shmop_size($memory) >= 100); shmop_delete($memory); }The changed input illustrates why output may differ with the chosen values or environment. Capacity is not the length of meaningful application content.
Practical Example: Using the Feature
The following example incorporates shmop_size into a workflow. Values such as paths, connection handles and configuration options must come from trusted application settings.
<?php
$memory = shmop_open(0x34593, "n", 0600, 128);
if ($memory !== false) { $data = "hello"; if (strlen($data) <= shmop_size($memory)) { shmop_write($memory, $data, 0); } shmop_delete($memory); }In a real application, check each operation result, validate values before use and clean up acquired resources. Capacity is not the length of meaningful application content.
Important Behavior and Edge Cases
- Purpose: Returns the capacity, in bytes, of a shared-memory block.
- Key limitation: Capacity is not the length of meaningful application content.
- Failure handling: Check return values and handle invalid inputs and unavailable operating-system or extension features where relevant.
Comparison With Related Functions
| Function or Approach | Best Fit |
|---|---|
shmop_size() | Returns the capacity, in bytes, of a shared-memory block. |
shmop_read() | Reads the stored bytes; shmop_size() reports the entire segment capacity. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Capacity is not the length of meaningful application content. | The correct approach depends on this behavior: Capacity is not the length of meaningful application content. |
| Ignoring errors or cleanup after the operation. | Validate inputs and check each result; close files, restore settings or release resources when the operation requires it. |
Key Takeaways
- Returns the capacity, in bytes, of a shared-memory block.
- Capacity is not the length of meaningful application content.
- Use the examples as starting points, and adapt environmental paths, resources and permissions rather than assuming fixed results.
shmop_size is useful when its specific behavior fits the problem. The safest implementations combine the correct API with input validation, error checking and resource cleanup.