Undefined index with POST

Question

I am trying to relearn some PHP basics for making a simple login script  however I get an error I have not received before I made the same script a little over a year ago and never had this error  I simplified the code as much as I could to test to see which area was problematic and here is the issue    lt  php  user     POST  username    if  user    null        echo  user      echo   is your username     else       echo  no username supplied       gt    Now this code works fine when I send a variable to the script  but when no variable is supplied it spits out an error  In theory this will be fine because if no username pass is supplied then an error is expected  I will be checking to make sure of this before the code is send to the script  however I fear that somehow a blank string may leak through and spit out some unknown error  Here is the error I get         Notice  Undefined index  username in C  wamp www verify login php on line 2  Call Stack      Time    Memory  Function    Location 1   0 0003  668576   main          verify login php 0   no username supplied  as you can see the code registers that no variable was supplied  but it gives out and error that I assume means that a variable was not found were one was expected or something like that  Can someone please clarify this for me

User · Answer

Use   if  isset   POST  user            do something     But you probably should be using some more proper validation  Try a simple regex or a rock-solid implementation from Zend Framework or Symfony    http   framework zend com manual en zend validate introduction html  http   symfony com doc current book validation html  Or even the built-in filter extension   http   php net manual en function filter-var php  Never trust user input  be smart  Don t trust anything  Always make sure what you receive is really what you expect  If it should be a number  make SURE it s a number   Much improved code    user   filter var   POST  user    FILTER SANITIZE STRING    isValid   filter var  user  FILTER VALIDATE REGEXP  array  options    gt  array  regexp    gt      a-zA-Z0-9           if   isValid           do something     Sanitization and validation

User · Answer

Try this   I use this everywhere where there is a   POST request     username isset   POST  username        POST  username           This is just a short hand boolean  if isset it will set it to   POST  username    if not then it will set it to an empty string   Usage example   if  username        echo  Field is blank    else   echo  Success

User · Answer

Instead of isset   you can use something shorter getting errors muted  it is    POST  field    Then  if the field is not set  you ll get no error printed on a page

User · Answer

In PHP  a variable or array element which has never been set is different from one whose value is null  attempting to access such an unset value is a runtime error    That s what you re running into  the array   POST does not have any element at the key  username   so the interpreter aborts your program before it ever gets to the nullity test   Fortunately  you can test for the existence of a variable or array element without actually trying to access it  that s what the special operator isset does   if  isset   POST  username          user     POST  username      echo  user    echo   is your username      else       user   null    echo  no username supplied       This looks like it will blow up in exactly the same way as your code  when PHP tries to get the value of   POST  username   to pass as an argument to the function isset    However  isset   is not really a function at all  but special syntax recognized before the evaluation stage  so the PHP interpreter checks for the existence of the value without actually trying to retrieve it    It s also worth mentioning that as runtime errors go  a missing array element is considered a minor one  assigned the E NOTICE level   If you change the error reporting level so that notices are ignored  your original code will actually work as written  with the attempted array access returning null  But that s considered bad practice  especially for production code   Side note  PHP does string interpolation  so the echo statements in the if block can be combined into one   echo   user is your username

User · Answer

Prior to PHP 5 2 0 and above you should use filter input   which is especially created for that to get a specific external user inputs such as get  post or cookie variables by name and optionally filters it to avoid any XSS Injection attacks on your site  For example   user   filter input INPUT POST   username     You may use one of INPUT GET  INPUT POST  INPUT COOKIE  INPUT SERVER  or INPUT ENV  By using optional 3rd argument  you can extend it by variety of filters  for validating  sanitizing  filtering or other   e g  FILTER SANITIZE SPECIAL CHARS  FILTER SANITIZE ENCODED  etc  For example   lt  php  search html   filter input INPUT GET   search   FILTER SANITIZE SPECIAL CHARS    search url   filter input INPUT GET   search   FILTER SANITIZE ENCODED   echo  quot You have searched for  search html  n quot   echo  quot  lt a href   search  search url  gt Search again  lt  a gt  quot     gt   The syntax is   mixed filter input   int  type   string  variable name    int  filter   FILTER DEFAULT    mixed  options       PHP 5  gt   5 2 0  PHP 7   See also  Why is better to use filter input

User · Answer

I know that this is old post but someone can help   function POST  index   default NULL           if isset   POST  index                          if  empty trim   POST  index                         return   POST  index                     return  default          This code above are my basic POST function what I use anywhere  Here you can put filters  regular expressions  etc  Is faster and clean  My advanced POST function is more complicate to accept and check arrays  string type  default values etc  Let s your imagination work here   You easy can check username like this    username   POST  username    if  username   null       echo    username  is in the house        Also I added  default string that you can define some default value if POST is not active or content not exists   echo   lt h1 gt   POST  title    Stack Overflow     lt  h1 gt      Play with it

User · Answer

Related question   What is the best way to access unknown array elements without generating PHP notice   Using the answer from the question above  you can safely get a value from   POST without generating PHP notice if the key does not exists   echo  arr   POST   username    no username supplied         will print   POST  username   or  no username supplied

User · Answer

try  if isset   POST  username         echo   POST  username     is your username   else     echo  no username supplied

User · Answer

When you say    user     POST  username      You re asking the PHP interpreter to assign  user the value of the   POST array that has a key  or index  of username  If it doesn t exist  PHP throws a fit   Use isset   POST  user    to check for the existence of that variable   if  isset   POST  user          user     POST  username

User · Answer

Your code assumes the existence of something    user     POST  username      PHP is letting you know that there is no  username  in the   POST array  In this instance  you would be safer checking to see if the value isset   before attempting to access it   if   isset    POST  username                    proceed            Alternatively  you could hi-jack the    operator to assign a default    user     POST  username       visitor      As long as the user s name isn t a falsy value  you can consider this method pretty reliable  A much safer route to default-assignment would be to use the ternary operator    user   isset    POST  username         POST  username      visitor

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