PHP beginner mistakes set

Please turn on all error prompts when doing development: error_reporting = E_ALL | E_STRICT
Blocking error prompts is equivalent to hiding your ears and stealing the bell.
Writing code in a standardized manner will reduce errors by half.

1: Why can’t I get the variable

I POST data name from one web page to another web page, why can’t I get any value when I output $name?

In PHP4.2 and later versions, register_global defaults to off
If you want to get the variables submitted from another page:

Method 1: Find register_global in PHP.ini and set it to on.
Method 2: Put this extract($_POST) at the front of the receiving web page; extract($_GET);(Note that there must be Session_Start() before extract($_SESSION)).
//extract ( array $var_array [, int $extract_type [, string $prefix ]] )

//This function is used to import variables from the array into the current symbol table. Accepts the associative array var_array as argument and uses the key //name as the variable name and the value as the variable's value. For each key/value pair a variable is created in the current symbol table, affected by the //extract_type and prefix parameters.
//import_request_variables ( string $types [, string $prefix ] ) is super global and has loopholes in $_ $*

Method 3: Read variables one by one $a=$_GET["a"];$b= $_POST["b"], etc. Although this method is troublesome, it is safer.

2: Debugging your program

You must know the value of a certain variable at runtime. This is what I did, create a file debug.php, its content is as follows:

PHP code: ---------------------------- -------------------------------------------------- --

Copy code

Ob_Start();
Session_Start();
Echo "

";<br> Echo "The _GET variables obtained on this page are:";<br> Print_R($_GET);<br> Echo " The _POST variables obtained on this page are: ";<br> Print_R($_POST);<br> Echo "The _COOKIE variables obtained on this page are: ";<br> Print_R($_COOKIE);<br> Echo "The _SESSION variables obtained on this page are :";<br> Print_R($_SESSION);<br> Echo "

";



-------------------------- -------------------------------------------------- ----

Then set include_path = "c:/php" in php.ini, and put debug.php in this folder.
You can include this file in each web page in the future and view the result Variable names and values.

3: How to use session

Everything related to session must call the function session_start() before;

Paying value for session is very simple, such as:


PHP code: ------- -------------------------------------------------- --------------------------

After php4.2, you can pay directly for the session:

PHP code:------ -------------------------------------------------- --------------------------

[php]
Session_Start();
$_SESSION["name"]="value";
[/ php]

------------------------------------------------- ----------------------------------

Cancel session like this:

PHP code:---- -------------------------------------------------- --------------------------

[php]
session_start();
session_unset();
session_destroy();
[/php ]

-------------------------------------------------- ----------------------------------


There is a BUG in canceling a certain session variable in php4.2 and above.



Note:

1: There cannot be any output before calling Session_Start(). For example, the following is wrong.
======================== ====================
1 line
2 lines [php]
3 lines Session_Start();//There was already output on the first line before
4 lines. ....
5 lines[/php]
======================================== ====


Tips 1:

Anytime "...headers already sent..." appears, it means that information is output to the browser before Session_Start().
It will be normal if you remove the output. (This error will also occur in COOKIE, and the cause of the error is the same)

Tips 2:

If your Session_Start() is placed in a loop statement, and it is difficult to determine where the information was output to the browser before, you can Use the following method:
Line 1 [php] Ob_Start(); [/php]
...Here is your program...



2: What is the error?

Warning: session_start(): open(/tmpsess_7d190aa36b4c5ec13a5c1649cc2da23f, O_RDWR) failed:....
Because you did not specify the storage path of the session file.

Solution:
(1) Create the folder tmp on the c drive
( 2) Open php.ini, find session.save_path, and change it to session.save_path= "c:/tmp"



4: Why do I only get the first half of the variable when I send it to another web page, and the one starting with a space? All lost


PHP code:--------------------------------------------- ----------------------------------------

[php]
$Var="hello php ";//Change to $Var=" hello php"; Try to get the result
$post= "receive.php?Name=".$Var;
header("location:$post");
[/php]

----------------- -------------------------------------------------- -------------

receive.php content:

PHP code:------------------------ -------------------------------------------------- ------

[php]
Echo "

";<br>Echo $_GET["Name"];<br>Echo "

";
[/php]

--- -------------------------------------------------- --------------------------


The correct method is:

PHP code:---------- -------------------------------------------------- --------------------

[php]
$Var="hello php";
$post= "receive.php?Name=".urlencode($ Var);
header("location:$post");
[/php]

----------------------------- -------------------------------------------------- -


You don’t need to use Urldecode() on the receiving page, the variables will be automatically encoded.


5: How to intercept Chinese characters of a specified length without ending with "[/php]", and the excess part will end with "... "Replace


Generally speaking, the variable to be intercepted comes from Mysql. First, make sure that the field length is long enough, usually char(200), which can hold 100 Chinese characters, including punctuation.

PHP code: --- -------------------------------------------------- --------------------------

[php]
$str="This character is so long,^_^";
$ Short_Str=showShort($str,4);//Intercept the first 4 Chinese characters, the result is: this character...
Echo "$Short_Str";
Function csubstr($str,$start,$len)
{
$ strlen=strlen($str);
$clen=0;
for($i=0;$i<$strlen;$i++,$clen++)
{
if ($clen>=$start+$len)
break ;
if(ord(substr($str,$i,1))>0xa0)
{
if ($clen>=$start)
$tmpstr.=substr($str,$i,2);
$i++;
}
else
{
if ($clen>=$start)
$tmpstr.=substr($str,$i,1);
}
}

return $tmpstr;
}
Function showShort ($str,$len)
{
$tempstr = csubstr($str,0,$len);
if ($str<>$tempstr)
$tempstr .= "..."; //To As for the ending, just modify it here.

return $tempstr;
}

-------------------------------- ----------------------------------------



6: Standardize your SQL statements


Add "`" in front of tables and fields, so that errors will not occur due to misuse of keywords.
Of course I do not recommend you to use keywords.

For example
$Sql="INSERT INTO `xltxlm` (`author`, `title`, `id`, `content`, `date`) VALUES ('xltxlm', 'use`', 1, 'criterion your sql string ' , '2003-07-11 00:00:00')"

"`"How to enter? On the TAB key.


7: How to prevent the string in Html/PHP format from being interpreted, but as it is Display


PHP code:--------------------------------------------- ----------------------------------------

[php]
$str="";
Echo "Interpreted: ".$str."
Processed:";
Echo htmlentities(nl2br($str));
[/php]

The nl2br() function inserts an HTML newline character (
) before each new line (n) in a string.
htmlentities(string,quotestyle,character-set)


quotestyle is optional. Specifies how single and double quotes are encoded.

ENT_COMPAT - Default. Only double quotes are encoded.
ENT_QUOTES - Encode double and single quotes.
ENT_NOQUOTES - Do not encode any quotes.

character-set

ISO-8859-1 - Default. Western Europe.
ISO-8859-15 - Western Europe (adds Euro symbol and French and Finnish letters).
UTF-8 - ASCII compatible multi-byte 8-bit Unicode
cp866 - DOS-specific Cyrillic character set
cp1251 - Windows-specific Cyrillic character set
cp1252 - Windows-specific Western European character set
KOI8-R - Russian
GB2312 - Simplified Chinese, country Standard character set
BIG5 - Traditional Chinese
----------------------------------------- ---------------------------------------



8: How to get it in the function Variable value outside the function


PHP code:--------------------------------------------- ----------------------------------------

[php]
$a= "PHP";
foo();
Function foo()
{
global $a;//Delete here and see what the result is
Echo "$a";
}
[/php]

---- -------------------------------------------------- --------------------------



9: How do I know what functions the system supports by default


PHP code:---- -------------------------------------------------- --------------------------

[php]
$arr = get_defined_functions();
Function php() {
}
echo "

";<br>Echo "Here displays all functions supported by the system, and custom functions phpn";<br>print_r($arr);<br>echo "

";
[/php]
-------- -------------------------------------------------- -----------------------


10: How to compare the difference between two dates


PHP code:--------- -------------------------------------------------- ---------------------

[php]
$Date_1="2003-7-15";//It can also be:$Date_1="2003- 6-25 23:29:14";
$Date_2="1982-10-1";
$Date_List_1=explode("-",$Date_1);
$Date_List_2=explode("-",$Date_2);
$d1=mktime(0,0,0,$Date_List_1[1],$Date_List_1[2],$Date_List_1[0]);
$d2=mktime(0,0,0,$Date_List_2[1],$ Date_List_2[2],$Date_List_2[0]);
$Days=round(($d1-$d2)/3600/24);
Echo "I have struggled for $Days days^_^";
[/php ]

(strtotime($Date_1) - strtotime($Date_2))/3600/24
----------------------------- -------------------------------------------------- -


11: Why after I upgraded PHP, the original program showed a full screen Notice: Undefined variable:


This is a warning, caused by the variable being undefined.
Open php.ini and find the bottom error_reporting, change to error_reporting = E_ALL & ~E_NOTICE

For Parse error error
error_reporting(0) cannot be turned off.
If you want to turn off any error prompts, open php.ini, find display_errors, set display_errors = Off. Any errors in the future No prompt will be given.

Then what is error_reporting?



12: I want to add a file at the beginning and end of each file. But adding one by one is very troublesome

1: Open the php.ini file
Set include_path= "c:"

2: Write two files
auto_prepend_file.php and auto_append_file.php and save them on the c drive, they will automatically be attached to the head and tail of each php file.

3: In php. Found in ini:
Automatically add files before or after any PHP document.
auto_prepend_file = auto_prepend_file.php; attached to the head
auto_append_file = auto_append_file.php; attached to the tail

In the future, each of your PHP files will be equivalent to

PHP Code:------------------------------------------------ --------------------------------

[php]
Include "auto_prepend_file.php" ;

... ....//Here is your program


Include "auto_append_file.php";
[/php]

---------------------- -------------------------------------------------- --------




13: How to use PHP to upload files



PHP code:----------------------- -------------------------------------------------- -------
[php]

Please select the file:

$upload_file=$_FILES['upload_file']['tmp_name'];
$upload_file_name=$_FILES['upload_file']['name'];

if($upload_file){
$file_size_max = 1000*1000;//1M limit file upload maximum capacity (bytes)
$store_dir = "d: /";//Storage location of uploaded files
$accept_overwrite = 1;//Whether overwriting the same file is allowed
// Check file size
if ($upload_file_size > $file_size_max) {
echo "Sorry, your file capacity is greater than Regulations";
exit;
}

//Check read and write files
if (file_exists($store_dir . $upload_file_name) && !$accept_overwrite) {
Echo "Files with the same file name exist";
exit;
}

//Copy the file to the specified directory
if (!move_uploaded_file($upload_file,$store_dir.$upload_file_name)) {
echo "Failed to copy file";
exit;
}

}

Echo "

You Uploaded file: ";
echo $_FILES['upload_file']['name'];
echo "
";
//The original name of the client machine file.

Echo "The MIME type of the file is:";
echo $_FILES['upload_file']['type'];
//The MIME type of the file, the browser needs to provide support for this information, such as "image/gif" .
echo "
";

Echo "Upload file size:";
echo $_FILES['upload_file']['size'];
//The size of the uploaded file, in bytes.
echo "
";

Echo "After the file is uploaded, it is temporarily stored as:";
echo $_FILES['upload_file']['tmp_name'];
//The temporary file name stored on the server after the file is uploaded.
echo "
";


$Erroe=$_FILES['upload_file']['error'];
switch($Erroe){
                                                                                                                                                               1:
                                                           .
Case 3: c Echo "files are only uploaded"; Break;
Case 4:
Echo "No files are uploaded"; break;
}
[/pHP]

------------------------------------------------------------------------------------------------------------------------ -------------------------------------------------- --------------------



14: How to configure the GD library


The following is my configuration process
1: Use dos command (can also be operated manually , copy all dll files in the dlls folder to the system32 directory) copy c:phpdlls*.dll c:windowssystem32
2: Open php.ini
set extension_dir = "c:/php/extensions/";
3:
extension =php_gd2.dll; Remove the comma in front of extension. If there is no php_gd2.dll, the same goes for php_gd.dll. Make sure this file does exist c:/php/extensions/php_gd2.dll
4: Run the following program to test

PHP code:------------------------------------------------ ----------------------------------

[php]
Ob_end_flush();
//Attention, here No information can be output to the browser before. Please pay attention to whether auto_prepend_file is set.
header ("Content-type: image/png");
$im = @imagecreate (200, 100)
or die ("Unable to create image" );
$background_color = imagecolorallocate ($im, 0,0, 0);
$text_color = imagecolorallocate ($im, 230, 140, 150);
imagestring ($im, 3, 30, 50, "A Simple Text String", $text_color);
imagepng ($im);
[/php]

-------------------------------- -------------------------------------------------- -



Click here to view the results



15: What is UBB code


UBB code is a variant of HTML, which is adopted by Ultimate Bulletin Board (a foreign BBS program, and many places in China also use this program) A special TAG.
Even if the use of HTML is prohibited, you can still use UBBCode? to achieve it. Maybe you prefer to use UBBCode? instead of HTML, even if the forum allows the use of HTML, because it uses less code and is safer.

Q3boy's UBB has examples, you can run the test directly


16: I want to modify the MySQL user and password

First of all, I must declare that in most cases, modifying MySQL requires root permissions in mysql.
So general users cannot change their passwords unless they request the administrator.

Method 1
Use phpmyadmin, this is the simplest, modify the user table of the mysql library,
But don’t forget to use the PASSWORD function.

Method 2
Using mysqladmin, this is a special case stated earlier.
　Mysqladmin -u root -p password mypasswd
　After entering this command, you need to enter the original password of root, and then the password of root will be changed to mypasswd.
　Change root in the command to your username, and you can change your own password.
　Of course, if your mysqladmin cannot connect to the mysql server, or you cannot execute mysqladmin,
　then this method is invalid.
　And mysqladmin cannot clear the password.

The following methods are all used at the mysql prompt and must have mysql root permissions:
　Method 3
　mysql> INSERT INTO mysql.user (Host,User,Password)
　VALUES('%','jeffrey', PASSWORD('biscuit'));
　mysql> FLUSH PRIVILEGES
　To be precise, this is adding a user with the username jeffrey and the password biscuit.
There is this example in the "mysql Chinese Reference Manual", so I wrote it out.
　Note to use the PASSWORD function, and then use FLUSH PRIVILEGES.

Method 4
Same as method 3, just using the REPLACE statement
Mysql> REPLACE INTO mysql.user (Host,User,Password)
VALUES('%','jeffrey',PASSWORD('biscuit'));
　mysql> FLUSH PRIVILEGES

Method 5
　Use the SET PASSWORD statement,
　　mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit');
　You must also use the PASSWORD() function,
　But there is no need to use FLUSH PRIVILEGES.

Method 6
　Use GRANT... IDENTIFIED BY statement
　mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit';
　The PASSWORD() function is unnecessary here, and there is no need to use FLUSH PRIVILEGES.

Note: PASSWORD() [does not] perform password encryption in the same way as Unix password encryption.


17: I want to know which website he connected to this page through



PHP code:-------------------------- -------------------------------------------------- ----

[php]
//You must enter through a super connection to have output
Echo $_SERVER['HTTP_REFERER'];
[/php]

------------- -------------------------------------------------- ------------------



18: What should you pay attention to when putting data into the database and taking it out to display on the page

When entering the database
$str=addslashes($str) ;
$sql="insert into `tab` (`content`) values('$str')";
When leaving the library
$str=stripslashes($str);
When displaying
$str=htmlspecialchars(nl2br( $str)) ;



addslashes() function adds a backslash before the specified predefined characters.

These predefined characters are:

single quote (')
double quote (")
backslash()
NULL

stripslashes() function removes backslashes added by addslashes() function.
htmlspecialchars( ) function converts some predefined characters into HTML entities

19: How to read the current address bar information



PHP code:-------------------- -------------------------------------------------- ----------

[php]
$s="http://{$_SERVER['HTTP_HOST']}:{$_SERVER["SERVER_PORT"]}{$_SERVER['SCRIPT_NAME' ]}";
$se='';
foreach ($_GET as $key => $value) {
$se.=$key."=".$value."&";
}
$se =Preg_Replace("/(.*)&$/","$1",$se);
$se?$se="?".$se:"";
echo $s."?$se";
[/php]
-------------------------------------------------- ------------------------------------




20: I clicked the back button, why before The filled-in items are missing

This is because you used session.
Solution:

PHP code:-------------------------- -------------------------------------------------- ---

[php]
session_cache_limiter('private, must-revalidate');
session_start();
..........
..........
[ /php]

------------------------------------------------ ----------------------------------



21: How to display IP address in pictures


PHP code:------------------------------------------------ ----------------------------------

[php]
Header("Content-type: image/png ");
$img = ImageCreate(180,50);
$ip = $_SERVER['REMOTE_ADDR'];
ImageColorTransparent($img,$bgcolor);
$bgColor = ImageColorAllocate($img, 0x2c,0x6D,0xAF ); // Background color
$shadow = ImageColorAllocate($img, 250,0,0); // Shadow color
$textColor = ImageColorAllocate($img, oxff,oxff,oxff); // Font color
ImageTTFText($ img,10,0,78,30,$shadow,"d:/windows/fonts/Tahoma.ttf",$ip); //Show background
ImageTTFText($img,10,0,25,28,$textColor ,"d:/windows/fonts/Tahoma.ttf","your ip is".$ip); // Display IP
ImagePng($img);
imagecreatefrompng($img);
ImageDestroy($img);
[/php]

-------------------------------------------------- ------------------------------------



22: How to get the user’s real IP


PHP code:------------------------------------------------ ----------------------------------

[php]
function iptype1 () {
if (getenv( "Http_client_ip") {
Return Getenv ("http_client_ip"); Forwardeded_For ")) {
Return Getenv ("HTTP_X_FORWARDED_FOR");
}
else {
return "none";
}
}
function iptype3 () {
if (getenv("REMOTE_ADDR")) {
return getenv("REMOTE_ADDR");
}
else {
Return "none";
}
}
function ip() {
$ip1 = iptype1();
$ip2 = iptype2();
$ip3 = iptype3();
if (isset($ip1) && $ip1 != "none" && $ip1 != "unknown") {
  return $ip1;
}
elseif (isset($ip2) && $ip2 != "none" && $ ip2 != "unknown") {
return $ip2;
}
elseif (isset($ip3) && $ip3 != "none" && $ip3 != "unknown") {
return $ip3;
}
else {
return "none";
}
}

Echo ip();
[/php]
-------------------------- -------------------------------------------------- ----



23: How to read all records within three days from the database

First of all, there must be a DATETIME field in the table to record the time,
The format is '2003-7-15 16:50:00'

SELECT * FROM `xltxlm` WHERE TO_DAYS(NOW()) - TO_DAYS(`date`) <= 3;


24: How to remotely connect to Mysql database


There is a host field in the mysql table where users are added, Change it to "%", or specify the IP address that allows the connection, so that you can call it remotely.

$link=mysql_connect("192.168.1.80:3306","root","");


25: How to use regular expressions

Click here
Special characters in regular expressions


26:Use After Apache, garbled characters appear on the homepage


Method one:
AddDefaultCharset ISO-8859-1 changed to AddDefaultCharset off

Method two:
AddDefaultCharset GB2312
==================== ======================================
tip:
GB2312 will be explained when everyone posts the code

If you change it to this, it will not happen
GB2312

10: How to compare the number of days between two dates, (simpler algorithm)


PHP code:-------- -------------------------------------------------- -----------------------

[php]
$Date_1="2003-7-15";//It can also be:$Date_1="2003 -7-15 23:29:14";
$Date_2="1982-10-1";
$d1=strtotime($Date_1);
$d2=strtotime($Date_2);
$Days=round(( $d1-$d2)/3600/24);
Echo "I have struggled for $Days days^_^";
[/php]

---------------- -------------------------------------------------- ---------------
round(123.456,2) = 123.46
ROUND ( numeric_expression , length )

round(123.456,-2) =100

When length is a positive number, numeric_expression rounds to the number of decimal places specified by length . When length is negative, numeric_expression is based on the left side of the decimal point as specified by Length; -------                                                                                                                                                  .45), CEILING(0.0)

The following is the result set:

--------- ================================================== ================

27: Why do single quotes and double quotes become ('") on the acceptance page


Solution:
Method 1: In php.ini Setting: magic_quotes_gpc = Off
Method 2: $str=stripcslashes($str)


28: How to keep the program running instead of stopping after more than 30 seconds


set_time_limit(60)//Maximum running time one Minutes
set_time_limit(0)//Run until the program ends by itself, or stop manually


29: Calculate the number of people currently online

Example 1: Use text to implement

PHP code:---------- -------------------------------------------------- -------------------

[php]
//First you must have permission to read and write files
//This program can be run directly, and an error will be reported the first time, You can do it later
$online_log = "count.dat"; //Save the file of the number of people,
$timeout = 30; //If there is no action within 30 seconds, it will be considered offline
$entries = file($online_log);

$temp = array();

for ($i=0;$i$entry = explode(",",trim($entries[$i]));
if (($entry[0] != getenv('REMOTE_ADDR')) && ($entry[1] > time() )) {
  array_push($temp,$entry[0].",".$entry[1]."n"); //Get the information of other viewers, remove the timeout ones, and save it in $temp
}
}

array_push($temp,getenv('REMOTE_ADDR').",".(time() + ($timeout))."n"); //Update the viewer's time
$users_online = count($ temp); //Calculate the number of people online

$entries = implode("",$temp);
//Write to file
$fp = fopen($online_log,"w");
flock($fp,LOCK_EX) ; //flock() does not work properly in NFS and some other network file systems
fputs($fp,$entries);
flock($fp,LOCK_UN);
fclose($fp);

echo "Current There is ".$users_online."人在线";

[/php]
-------------------------------- ----------------------------------------

Example 2:
Use database to implement online users


30: What is a template and how to use it


Here are several articles about templates

I use phplib template
Here are the uses of several of the functions

$T->Set_File("Any definition","template file.tpl");

$T->Set_Block("defined in set_file","" ,"define whatever you want");

$T->Parse("defined in Set_Block","",true);

$T->Parse( "Output the results at will", "defined in Set_File");

Set the loop format to:



How to generate a static web page from a template

PHP code:--------------------------------------------- ----------------------------------------

[php]
//here Use phplib template
                                                                                                     $tpl->get("output");// $output is the entire web page content


function wfile($file,$content,$mode='w') {
$oldmask = umask(0);
$fp = fopen($file, $mode);
if (!$fp) return false;
fwrite($fp,$content);
fclose($fp);
umask($oldmask);
return true;
}
//Write to file
Wfile($FILE,$output);
header("location:$FILE");//Redirect to the generated web page
}
[/php]
---- -------------------------------------------------- --------------------------



phplib download address smarty download address


31: How to use php to interpret characters

For example: Input 2+2*(1+2) and automatically output 8
You can use the eval function

PHP code:-------------------------- -------------------------------------------------- ----

[php]
$str=$_POST['str'];
eval("$o=$str;");
Echo "$o";
[/php]

------ -------------------------------------------------- -----------------------


In addition, you must be particularly careful when using this function!!
What will be the result if someone enters format: d:?