How to Use ftell and fread Together to Read Data from a Specific Position in a File?

gitbox 2025-09-11

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How to Use ftell and fread Together to Read Data from a Specific Position in a File?

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In PHP, when handling files, sometimes we need to read data from a specific position in the file. The ftell() and fread() functions can work well together to accomplish this task.

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1. ftell() Function

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The ftell() function returns the current position of the file pointer (in bytes). With ftell(), we can determine where we are in the file during reading.

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2. fread() Function

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The fread() function is used to read a specified length of data from a file. Its basic usage is as follows:

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<br>
fread(resource $handle, int $length);<br>

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Here, $handle is the file resource, and $length is the number of bytes to read.

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3. Example of Using Them Together

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Suppose we have a text file called example.txt, and we want to read 20 bytes starting from the 10th byte:

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// Check the current position
\$position = ftell(\$handle);
echo 'Current pointer position: ' . \$position . \"\\n\";

// Read 20 bytes
\$data = fread(\$handle, 20);
echo 'Data read: ' . \$data;

fclose(\$handle);

} else {
echo 'Unable to open file';
}
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In this example:

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Use fseek(\$handle, 10) to move the file pointer to the 10th byte.
Use ftell(\$handle) to confirm the current pointer position.
Use fread(\$handle, 20) to read 20 bytes of data from the current pointer position.

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4. Summary

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By combining fseek(), ftell(), and fread(), we can precisely read data from any position in a file. This is especially useful when working with large files or when specific content needs to be skipped.

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