The php setcookie value is null or a null string (delete cookie)

For a long time, when deleting cookies in php
Bool setcookie (string $ name [, string $ value [, int $ expire = 0 [, string $ path [, string

$ Domain [, bool $ secure = false [, bool $ httponly = false])

$ Value can be written at will, and $ expire can be set to a time that has passed.

This is also written in the official document:

Http://www.php.net/manual/en/function.setcookie.php

Example #2 setcookie () delete example
When deleting a cookie you shoshould assure that the expiration date is in the past, to trigger

The removal mechanic in your browser. Examples follow how to delete cookies sent in previous

Example:

The code is as follows:	Copy code
<? Php // Set the expiration date to one hour ago Setcookie ("TestCookie", "", time ()-3600 ); Setcookie ("TestCookie", "", time ()-3600 ,"/~ Rasmus/"," example.com ", 1 ); ?>

Today, I encountered a strange thing. When I set the cookie, I passed an empty string to $ value, and the result was that the cookie was deleted.

...

The code is as follows:	Copy code
$ Name = "post_url "; $ Value = ""; Setcookie ($ name, $ value, time () + 60*60*3 ,"/"); Delete_cookie

Rather puzzled.

Go to php 5.4.13 source code:

Ext/standard/head. c

The code is as follows:

Copy code

173 PHP_FUNCTION (setcookie) 174 { 175 char * name, * value = NULL, * path = NULL, * domain = NULL; 176 long expires = 0; 177 zend_bool secure = 0, httponly = 0; 178 int name_len, value_len = 0, path_len = 0, domain_len = 0; 179 180 if (zend_parse_parameters (ZEND_NUM_ARGS () TSRMLS_CC, "s | slssbb", & name, 181 & name_len, & value, & value_len, & expires, & path, 182 & path_len, & domain, & domain_len, & secure, & httponly) = FAILURE ){ 183 return; 184} 185 186 if (php_setcookie (name, name_len, value, value_len, expires, path, path_len, domain, Domain_len, secure, 1, httponly TSRMLS_CC) = SUCCESS ){ 187 RETVAL_TRUE; 188} else { 189 RETVAL_FALSE; 190} 191}       76 PHPAPI int php_setcookie (char * name, int name_len, char * value, int value_len, time_t Expires, char * path, int path_len, char * domain, int domain_len, int secure, int url_encode, Int httponly TSRMLS_DC) 77 { 78 char * cookie, * encoded_value = NULL; 79 int len = sizeof ("Set-Cookie :"); 80 char * dt; 81 sapi_header_line ctr = {0 }; 82 int result; 83 84 if (name & strpbrk (name, "=,; trn1314 ")! = NULL) {/* man isspace for 13 And 14 */ 85 zend_error (E_WARNING, "Cookie names cannot contain any of the following '= ,; \ T \ r \ n \ 013 \ 014 '"); 86 return FAILURE; 87} 88 89 if (! Url_encode & value & strpbrk (value, ",; trn1314 ")! = NULL) {/* man Isspace for 13 and 14 */ 90 zend_error (E_WARNING, "Cookie values cannot contain any of the following ',; \ T \ r \ n \ 013 \ 014 '"); 91 return FAILURE; 92} 93 94 len + = name_len; 95 if (value & url_encode ){ 96 int encoded_value_len; 97 98 encoded_value = php_url_encode (value, value_len, & encoded_value_len ); 99 len + = encoded_value_len; 100} else if (value ){ 101 encoded_value = estrdup (value ); 102 len + = value_len; 103} 104 if (path ){ 105 len + = path_len; 106} 107 if (domain ){ 108 len + = domain_len; 109} 110 111 cookie = emalloc (len + 100 ); 112 113 if (value & value_len = 0 ){ 114 /* 115 * MSIE doesn't delete a cookie when you set it to a null value 116 * so in order to force cookies to be deleted, even on MSIE, we 117 * pick an expiry date in the past 118 */ 119 dt = php_format_date ("D, d-M-Y H: I: s T", sizeof ("D, d-M-Y H: I: s T")-1, 1, 0 TSRMLS_CC ); 120 snprintf (cookie, len + 100, "Set-Cookie: % s = deleted; expires = % s", name, dt ); 121 efree (dt ); 122} else { 123 snprintf (cookie, len + 100, "Set-Cookie: % s = % s", name, value? Encoded_value: ""); 124 if (expires> 0 ){ 125 const char * p; 126 strlcat (cookie, "; expires =", len + 100 ); 127 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 ); 128/* check to make sure that the year does not exceed 4 digits in length */ 129 p = zend_memrchr (dt, '-', strlen (dt )); 130 if (! P | * (p + 5 )! = ''){

The value type in the parameter is char * in C, and value_len indicates its length.
If value_len is 0, the following cookie is written:
The value is "deleted" and the expiration time is Thu. 01-Jan-1970 08:00:01 CST or Thu, 01-Jan-1970 00:00:01

GMT

It seems that setcookie ($ name, "") can indeed delete this cookie...
Similarly, in php, strval (NULL) === "", so setcookie ($ name, NULL) is equivalent to setcookie ($ name,

You can also delete this cookie.

In addition, I'm curious about the following:

The code is as follows:	Copy code
If (value & value_len = 0 ){ } Else { }

Else contains the case where value is null. What is the case?

It seems that setcookie ($ name, "") can indeed delete this cookie...
Similarly, in php, strval (NULL) === "", so setcookie ($ name, NULL) is equivalent to setcookie ($ name,

You can also delete this cookie.

In addition, I'm curious about the following:

The code is as follows:	Copy code
If (value & value_len = 0 ){ } Else { }

Else contains the case where value is null. What is the case?