php cannot delete cookies

Let’s first look at the mechanism of related cookies.

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:

<?php
//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 what almost all PHP programmers do. 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.

The following code can be found near line 99 of ext/standard/head.c in the php5.20 Linux source package:

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);
    }
}

It is clear in the source code Display "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 conclude that using "setcookie($cookiename, '');" or "setcookie($cookiename, NULL);" in php will delete cookies.

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