How to implement "when the name does not exist in the database, go to the error page." ”？

Dear Friends: This code is "Query password first step: Enter the member name", want to achieve the effect: when the name does not exist in the database, go to the error page.
I always show this code: Warning:cannot Modify Header Information-headers already sent by (output started at F:\PHPSites\member\getpwd 1-1.php:23) in F:\PHPSites\member\getpwd1-1.php on line 36
How should we change it? Thanks a lot!

 
  
 
  
 
  
 
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Reply to discussion (solution)

Output at 23 lines of getpwd1-1.php
Lead to the header ("location:message-1.php?error=3"); Error

Is it really necessary to check that output first? Can you adjust to somewhere else?
If not, can be in require_once (' connections/member.php '); Before adding
Ob_start ();
To avoid

Output at 23 lines of getpwd1-1.php
Lead to the header ("location:message-1.php?error=3"); Error

Is it really necessary to check that output first? Can you adjust to somewhere else?
If not, can be in require_once (' connections/member.php '); Before adding
Ob_start ();
To avoid
......

Moderator Adult: I put up is getpwd1-1.php all the code, how to adjust?
If in require_once (' connections/member.php '); Before adding Ob_start (), then go directly to the error page, rather than "Enter the nonexistent user name and go to the error page". Please advise, thank you very much!

Careless, not verifying the file name.
Move content from 16 to 33 rows (with 33 rows) to the back of the 39 line

Another 10 to 14 rows should be in a conditional branch of 7 rows

Careless, not verifying the file name.
Move content from 16 to 33 rows (with 33 rows) to the back of the 39 line

Another 10 to 14 rows should be in a conditional branch of 7 rows

Moderator: I follow your instructions to change, such as the next, but still go directly to the error page Ah!

 
  
 
  
 
  
 
  
 
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5 to 21 lines change to

Think for yourself, ask what to write like this?

5 to 21 lines change to
PHP code?123456789101112131415
Originally can this, finally put this logic clear, thank you moderator adult!

