How to Use the strftime Function to Get the Numeric Representation of the Day of the Week? Easily Handle Date Conversion

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// This part is unrelated to the article content, it can be any PHP code</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Welcome to the PHP Date Tool!\n"</span></span><span>;
</span><span><span class="hljs-variable">$today</span></span><span> = </span><span><span class="hljs-title function_ invoke__">date</span></span><span>(</span><span><span class="hljs-string">"Y-m-d"</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Today's date is: <span class="hljs-subst">$today</span></span></span><span>\n";
</span><span><span class="hljs-meta">?&gt;</span></span><span>
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<p></span><?php<br>
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<p>Article Body: How to Use the strftime Function to Get the Numeric Representation of the Day of the Week? Easily Handle Date Conversion</p>
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<p>In PHP, sometimes we need to convert a date into its numeric representation of the day of the week (commonly 0 for Sunday, 1 for Monday, and so on).</p>
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<p>For this need, PHP provides a very handy function — strftime().</p>
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<p>Introduction to strftime</p>
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<p>The strftime() function returns formatted date and time information based on a given format string. Its basic syntax is as follows:</p>
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<p>string strftime(string $format [, int $timestamp = time()])</p>
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<p>$format: The format string, for example "%w" represents the numeric value of the day of the week (0-6, 0=Sunday).</p>
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<p>$timestamp: An optional timestamp. If not specified, the current time is used.</p>
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<p>Getting the Numeric Representation of the Day of the Week</p>
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<p>Below is an example of converting a specific date into the numeric value of the day of the week:<br>
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<p>// Set the timezone to avoid timezone offsets<br>
date_default_timezone_set('Asia/Shanghai');</p>
<p>// Suppose we have a date string<br>
$dateStr = "2025-08-28";</p>
<p>// Convert the date string into a timestamp<br>
$timestamp = strtotime($dateStr);</p>
<p>// Use strftime to get the numeric value of the day of the week<br>
$weekNumber = strftime("%w", $timestamp);</p>
<p>echo "The date $dateStr corresponds to weekday number: $weekNumber\n"; // Output: 4, which means Thursday</p>
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<p>3. Key Points</p>
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<p>%w Format Symbol:</p>
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<p>0 = Sunday</p>
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<p>1 = Monday</p>
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<p>2 = Tuesday</p>
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<p>3 = Wednesday</p>
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<p>4 = Thursday</p>
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<p>5 = Friday</p>
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<p>6 = Saturday</p>
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<p>Timestamp Conversion:</p>
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<p>Using strtotime() makes it easy to convert a date string into a timestamp, ensuring compatibility with the strftime function.</p>
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<p>Complete Function Example</p>
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<p>If you want to reuse it often, you can wrap it into a function:<br>
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<p>function getWeekNumber($date) {<br>
$timestamp = strtotime($date);<br>
return strftime("%w", $timestamp);<br>
}</p>
<p>// Test the function<br>
echo "Using the wrapped function: The date $dateStr corresponds to weekday number: " . getWeekNumber($dateStr) . "\n";</p>
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<p>5. Summary</p>
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<p>By using strftime("%w", $timestamp), you can easily get the numeric value of the day of the week for a given date.</p>
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<p data-is-last-node="">Combined with strtotime(), you can handle any date string format and quickly convert dates.<br>
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