Detailed explanation of how to delete cookie instances in php

This article mainly shares with you the detailed explanation of how to delete cookie instances in PHP. Let's first look at the mechanism of related cookies, hoping to help everyone.

bool setcookie ( string name [, string value [, int expire [, string path [, string domain [, bool secure]]]]] )

To delete a cookie, you need to ensure that its expiration date is in the past to trigger the browser's deletion mechanism.

The following example illustrates how to delete the cookie just set:

//将过期时间设为一小时前setcookie("TestCookie", "", time() - 3600);
setcookie("TestCookie", "", time() - 3600, "/~rasmus/", ".utoronto.ca", 1);
?>

The way to delete a cookie is to set the validity period of the cookie to before the current time. This is also the case for almost all cookies. All PHP programmers do this.

Later, a friend who was new to PHP told me that he wanted to set the value of a cookie to empty in the program, but the cookie was deleted directly. My first reaction at the time was that I didn't believe it, so I tested it:

setcookie("testcookie", '');
print_r($_COOKIE);

The result was that the entire $_COOKIE array was empty, not just $_COOKIE['testcookie']. So I used winsock to capture the packet and observed the returned http header. I found that the http header turned out to be "Set-Cookie: testcookie=deleted; expires=Mon, 18-Jun-2007 02:42:33 GMT", which means "setcookie("testcookie ", '');" indeed deletes the cookie testcookie directly, and there is no explanation at all in the PHP manual about this situation.

Finally read the PHP source code and finally discovered the truth (this is the benefit of open source, if there is any unclear inside story, just check the source code directly).

Copy the code as follows:

if (value && value_len == 0) {
    /* 
     * MSIE doesn't delete a cookie when you set it to a null value
     * so in order to force cookies to be deleted, even on MSIE, we
     * pick an expiry date 1 year and 1 second in the past
     */
    time_t t = time(NULL) - 31536001;
    dt = php_format_date("D, d-M-Y H:i:s T", sizeof("D, d-M-Y H:i:s T")-1, t, 0 TSRMLS_CC);
    sprintf(cookie, "Set-Cookie: %s=deleted; expires=%s", name, dt);
    efree(dt);
} else {
    sprintf(cookie, "Set-Cookie: %s=%s", name, value ? encoded_value : "");
    if (expires > 0) {
        strcat(cookie, "; expires=");
        dt = php_format_date("D, d-M-Y H:i:s T", sizeof("D, d-M-Y H:i:s T")-1, expires, 0 TSRMLS_CC);
        strcat(cookie, dt);
        efree(dt);
    }
}

The source code clearly shows "if (value && value_len == 0)". When "value_len" is 0, "sprintf(cookie, "Set-Cookie: %s=deleted; expires=%s", name, dt);" will send the http header to delete the cookie to the browser.

Finally we can draw the conclusion: using "setcookie($cookiename, '');" or "setcookie($cookiename, NULL);" in php will delete cookies, but of course there is no such manual.

Isn’t it very simple? Sometimes we still need to read the php source code carefully.

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Detailed explanation of getting cookies and deleting cookies using JavaScript

How to delete cookies in php

php cookie class (set, get, delete cookie value)

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