In PHP, SplFileObject::fwrite() is useful when your application needs a specific operation rather than manually reproducing it. Writes bytes from a string to the stream and returns the number of bytes written.
The SplFileObject class combines file I/O with iterator behavior. Close the object before cleaning up a temporary file.
What Is fwrite() in PHP?
Writes bytes from a string to the stream and returns the number of bytes written.
Signature:
SplFileObject::fwrite(string $data, int $length = 0): mixedParameters:
$data— Raw bytes or text passed to the operation.$length— Requested byte count or upper bound; reads can return fewer bytes.
Return value: The return type depends on the result of this operation; inspect errors and exceptions as documented for the API..
Example 1: Basic Usage
This first example shows the method or function in a minimal context. For environment-dependent operations, adapt the required path, stream or connection before running it.
<?php
$tempPath = tempnam(sys_get_temp_dir(), "php-guide-");
file_put_contents($tempPath, "First line\nSecond line\n");
$file = new SplFileObject($tempPath, "r+");
$result = $file->fwrite('New data\n');
var_dump($result);
$file = null;
unlink($tempPath);
The important operation is SplFileObject::fwrite(). Writes bytes from a string to the stream and returns the number of bytes written.
Example 2: Another Input or Scenario
The next example changes the input or surrounding context to show how the operation behaves in a second situation.
<?php
$tempPath = tempnam(sys_get_temp_dir(), "php-guide-");
file_put_contents($tempPath, "Name,Score\nAda,93\nLeo,88\n");
$file = new SplFileObject($tempPath, "r+");
$result = $file->fwrite('New data\n');
var_dump($result);
$file = null;
unlink($tempPath);
Compare the inputs and the handling of the return value with the first example. Avoid assuming that filesystem paths, resource states or binary bytes are interchangeable.
Practical Example: Applying the Operation
This example illustrates how the operation fits into a small application workflow. Paths, streams and secrets must be created or provided securely by the calling application.
<?php
$tempPath = tempnam(sys_get_temp_dir(), "php-guide-");
file_put_contents($tempPath, "Name,Score\nAda,93\nLeo,88\n");
$file = new SplFileObject($tempPath, "r+");
$file->setFlags(SplFileObject::DROP_NEW_LINE);
$result = $file->fwrite('New data\n');
var_dump($result);
$file = null;
unlink($tempPath);
Practical note: Writes bytes from a string to the stream and returns the number of bytes written.
Important Behavior and Edge Cases
- Writes bytes from a string to the stream and returns the number of bytes written.
- Check failure values and exceptions; do not assume every environment supports the same stream wrapper, extension or filesystem capability.
- When handling paths, streams or external input, validate inputs before using results and release resources after use.
Comparison With Related Functions
| Function or Method | Behavior |
|---|---|
SplFileObject::fwrite() | writes a string of raw bytes. |
fputcsv() | writes a correctly escaped CSV row. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
Assuming fwrite() can be used without its required setup | Provide the correct file, stream, state, key or object before calling it; Writes bytes from a string to the stream and returns the number of bytes written. |
| Mixing byte offsets, line numbers and CSV records | Read the method contract: seek() targets line numbers, while fseek() and ftell() work with byte offsets. |
| Assuming every read returns a whole record | Handle end-of-file, empty lines and partial reads correctly; configure CSV handling when reading CSV. |
Key Takeaways
SplFileObject::fwrite()writes bytes from a string to the stream and returns the number of bytes written.- Use appropriate input types and verify results before continuing.
- Prefer specialized, safer APIs when the operation concerns untrusted input, encryption or network traffic.
In summary: Writes bytes from a string to the stream and returns the number of bytes written. Build in error handling and use this function where its specific behavior matches the application requirements.