Frequently Asked Questions for PHP Beginners

The fourteen most troublesome problems for PHP beginners

Management reminder: This post was pinned to the top by haowubai (2009-04-16) [1] Variables get, post, session cannot be passed between pages in the latest PHP version Automatic global variables are turned off, so to get the submitted variables from the previous page, use $_GET['foo'], $_POST['foo'], $_SESSION['foo']. Of course, you can also modify the automatic global variables to be on (php.ini changed to register_globals = On); considering compatibility, it is better to force yourself to be familiar with the new writing method.

【2】When apache uses the get method to pass Chinese parameters under Win, an error will occur:

　test.php?a=Hello&b=你好

　Passing parameters will cause an internal error
　
　Solution: "test. php ?a=".urlencode(Hello)."&b=".urlencode(Hello)

【3】session under win does not work properly

　php .ini default session.save_path = /tmp

This is obviously a configuration under Linux. PHP under win cannot read and write the session file, causing the session to be unusable. Just change it to an absolute path. For example, session.save_path = c:windows emp

【4】Display error message

　 When display_errors = On and error_reporting = E_ALL in php.ini, all errors and prompts will be displayed. It is best to turn them on during debugging for error correction. If you use the previous php writing method, most of the error messages are about undefined variables. There will be a prompt when a variable is called before it is assigned a value. The solution is to detect or shield it.

　For example, to display $foo, you can if(isset($foo)) echo $foo or echo @$foo

【5】mail() cannot send emails under Win

　 Sendmail configured under Linux can be sent, You need to call the smtp server to send emails under win, modify the SMTP of php.ini = ip //ip is an smtp server without verification function (hard to find online)

　The best solution for php to send emails is to use socket Send directly to the other party's email server without a forwarding server.

【6】If the password is not set for the initial installation of mysql, you should use update mysql.user set password="yourpassword" where user="root" to change the password

【7】header already sent

This error usually occurs when you It appears when using HEADER. It may be due to several reasons: You PRING or ECHO before using HEADER. There is a blank line in front of your current file. You may have INCLUDEd a file and there is a blank line at the end of the file or the output will also appear. This kind of mistake. !

【8】No change after changing php .ini

　 Restart the web server, such as IIS, Apache, etc., and then the latest settings will be applied.

【9】php is installed on 00 (the installation method of ISAPI, please ask experts for advice)

　 PHP's php isapi.dll seems to have some conflicts with 00, and can only be installed in CGI mode

　 Step 1, first go to www.php.net There is an installation program. I installed it: php -..-installer.exe. You can also find the latest version. Make sure your IIS6.0 is started before installing php -..-installer.exe. and be able to access. After installation, go to the default website-->Application configuration.

　 Step 2: Click web service extension --> Create a new web service extension.

　Step 3: Extension-->php, then add

Step 4: Find the path to php.exe and add it.

　Step 5: Just confirm! ​
​
​ Step 6: Select the PHP service extension and click Allow.

【10】Sometimes the sql statement does not work and the database operation fails. The easiest way to debug is to echo the sql sentence and see if the value of the variable can be obtained.

【11】The difference between include and require

There is not much difference between the two. If the file to be included does not exist, include will prompt notice, and then continue to execute the following statement, require will prompt a fatal error and exit.

According to my testing, under the win platform, they are included first and then executed, so it is best not to have include or require statements in the included files, which will cause directory confusion. Maybe the situation is different under *nux, I haven't tested it yet.

　If a file does not want to be included multiple times, you can use include_once or require_once## to read and write document data.

function r($file_name) {
$filenum=@fopen($file_name,"r");
@flock($filenum,LOCK_SH);
$file_data=@fread($filenum,filesize($file_name)) ;
@fclose($filenum);
return $file_data;
}
function w($file_name,$data,$method="w"){
$filenum=@fopen($file_name,$method);
flock ($filenum,LOCK_EX);
$file_data=fwrite($filenum,$data);
fclose($filenum);
return $file_data;
}
【12】The difference between isset() and empty()

　Both are used to test variables, but isset() tests whether a variable has been assigned a value, while empty() tests whether a variable that has been assigned a value is empty.

　 If a variable is referenced in PHP without being assigned a value, it is allowed, but there will be a notice prompt. If a variable is assigned a null value, $foo="" or $foo=0 or $foo=false, then empty ($foo) returns true, isset($foo) also returns true, which means assigning a null value will not unregister a variable.
　
　 To unregister a variable, you can use unset($foo) or $foo=NULL

【13】Mysql query statement contains keywords

　When php queries mysql, sometimes the mysql table name or column name has key words words, there will be errors in the query at this time. For example, if the table name is order, an error will occur during the query. The simple way is to add `[above the tab key] to the table name or column name in the sql statement to distinguish it, for example, select * from `order`

【14】Through HTTP protocol There are two ways to upload multiple files at one time, which are two implementations of the same method. The specific procedures need to be designed by yourself.

　、Set multiple file input boxes in the form and name them with arrays, as follows:

＜form action="" method=post＞

＜input type=file name=usefile[]＞

＜input type =file name=usefile[]＞
＜input type=file name=usefile[]＞
＜/form＞
In this way, do the following test on the server side:

echo "＜pre＞";

print_r($_FILES) ;

echo "＜/pre＞";
　 Set multiple file input boxes in the form, but with different names, as follows:

＜form action="" method=post＞

＜input type=file name=usefile_a＞

＜input type=file name=usefile_b＞
＜input type=file name=usefile_c＞
＜/form＞
Do the same test on the server side:

echo "＜pre＞";

print_r($_FILES);

echo "＜/pre＞";