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In PHP, rewind() is a commonly used file operation function that resets the file pointer to the beginning of the file. It is often used when you need to reread a file. However, when using rewind(), you may encounter a “resource cannot be rewound” error. This error usually occurs when the file resource has already been closed, or when the resource itself does not support rewinding.
In PHP, the rewind() function is used to reset an already opened file pointer back to the start of the file. The function prototype is as follows:
<span><span><span class="hljs-keyword">bool</span></span><span> </span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(resource </span><span><span class="hljs-variable">$file</span></span><span>);
</span></span>Parameter: $file is a file resource opened by fopen().
Return Value: On success, rewind() returns true; on failure, it returns false.
The root cause of this error usually falls into the following scenarios:
Before calling rewind(), make sure the file resource hasn’t been closed prematurely. If the file resource has been closed using fclose(), any further operations on that resource—including rewind()—will fail and trigger an error.
Example:
<span><span><span class="hljs-variable">$file</span></span><span> = </span><span><span class="hljs-title function_ invoke__">fopen</span></span><span>(</span><span><span class="hljs-string">'example.txt'</span></span><span>, </span><span><span class="hljs-string">'r'</span></span><span>);
</span><span><span class="hljs-title function_ invoke__">fclose</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>);
</span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>); </span><span><span class="hljs-comment">// Error: Resource cannot be rewound</span></span><span>
</span></span>The rewind() function requires a valid file resource as its argument. Passing an invalid resource, or a resource of the wrong type, will result in an error. For example, passing null or a closed resource.
Example:
<span><span><span class="hljs-variable">$invalid_resource</span></span><span> = </span><span><span class="hljs-literal">null</span></span><span>;
</span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(</span><span><span class="hljs-variable">$invalid_resource</span></span><span>); </span><span><span class="hljs-comment">// Error: Resource cannot be rewound</span></span><span>
</span></span>Certain stream types in PHP do not support the rewind() operation. For example, some special streams opened via fopen() (such as remote URLs or pipes) may not support resetting the pointer. For these streams, calling rewind() will fail with a “resource cannot be rewound” error.
Example:
<span><span><span class="hljs-variable">$file</span></span><span> = </span><span><span class="hljs-title function_ invoke__">fopen</span></span><span>(</span><span><span class="hljs-string">'http://example.com'</span></span><span>, </span><span><span class="hljs-string">'r'</span></span><span>); </span><span><span class="hljs-comment">// Open remote file</span></span><span>
</span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>); </span><span><span class="hljs-comment">// Error: Resource cannot be rewound</span></span><span>
</span></span>If the file pointer has moved to the end of the file, calling rewind() may not throw an immediate error, but without proper checks, it may cause unexpected behavior. Therefore, it’s best practice to perform necessary file checks before calling rewind().
Example:
<span><span><span class="hljs-variable">$file</span></span><span> = </span><span><span class="hljs-title function_ invoke__">fopen</span></span><span>(</span><span><span class="hljs-string">'example.txt'</span></span><span>, </span><span><span class="hljs-string">'r'</span></span><span>);
</span><span><span class="hljs-title function_ invoke__">fseek</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>, </span><span><span class="hljs-number">100</span></span><span>); </span><span><span class="hljs-comment">// Move file pointer to a certain position</span></span><span>
</span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>); </span><span><span class="hljs-comment">// Normally resets pointer to the beginning</span></span><span>
</span></span>Check if the File Has Been Closed:
Before calling rewind(), ensure the file resource is open and has not been accidentally closed. Use simple conditional checks to confirm this.
<span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">is_resource</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>)) {
</span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>);
} </span><span><span class="hljs-keyword">else</span></span><span> {
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"File resource is unavailable or already closed"</span></span><span>;
}
</span></span>Verify the Resource Type:
Ensure the argument passed to rewind() is a valid file resource. If unsure, you can check with the is_resource() function.
Check If the Stream Supports Rewinding:
If you’re working with remote files or special streams, verify whether they support the rewind() operation. Refer to the PHP manual for details on specific stream behaviors and limitations.
Ensure the File Pointer Hasn’t Been Unexpectedly Moved:
If the file pointer is at the end of the file, try using fseek() to move it to another position before calling rewind().
Use Error Handling:
Suppress error messages with the @ operator and use error_get_last() to retrieve detailed error information to aid troubleshooting.
<span><span><span class="hljs-keyword">if</span></span><span> (@</span><span><span class="hljs-title function_ invoke__">rewind</span></span><span>(</span><span><span class="hljs-variable">$file</span></span><span>) === </span><span><span class="hljs-literal">false</span></span><span>) {
</span><span><span class="hljs-variable">$error</span></span><span> = </span><span><span class="hljs-title function_ invoke__">error_get_last</span></span><span>();
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Error message: "</span></span><span> . </span><span><span class="hljs-variable">$error</span></span><span>[</span><span><span class="hljs-string">'message'</span></span><span>];
}
</span></span>The “resource cannot be rewound” error usually occurs when the file resource has already been closed, when an invalid resource is passed, or when the stream itself doesn’t support rewinding. To troubleshoot, first check the validity of the resource, confirm the file hasn’t been closed, and verify whether the stream supports rewinding. With proper error checking and conditional handling, this issue can usually be effectively avoided and resolved.
