A warning is not reported for the output before the header in php.

No output is available before header or session_start (). Otherwise, a warning error is reported, but why not. Version: wamp {code...} used in 5.3.5 ...} directly skip and change to session_start () without reporting the error level php. ini sets error_rep... no output is available before header or session_start (). Otherwise, a warning error is reported, but why not.
Version: 5.3.5
Wamp used

    
 
Skip directly and change it to session_start ().
Error level php. ini is set to error_reporting = E_ALL | E_STRICT
                                                    
Reply content:
No output is available before header or session_start (). Otherwise, a warning error is reported, but why not.
Version: 5.3.5
Wamp used
    
  
Skip directly and change it to session_start ().
Error level php. ini is set to error_reporting = E_ALL | E_STRICT
                                                                
                                    
Check whether output_buffering is enabled in phpinfo. If yes, there is no problem.
                                        
                                    
Check whether there is any warning prompt:
  
  

   
   
Check whether there is any print on the webpage. you have read it. No
   
   
Check whether there is any error log. The default xampp/wamp settings are more secure (rather than easy-to-use development by default) and do not directly display the error information on the webpage.
  
  
If you have read all the logs, you still cannot find the warning record. Check why the logs are not displayed and not logged. (assume that a warning is generated ):
Print phpinfo () and check which php. ini file is loaded in your runtime environment. After locating the php. ini file
  
  

   
   
Check the error_reporting settings (you have checked, but are not sure if other INI files are used)
   
   
Check display_error settings
   
   
Check error_log settings
  
  
If the above check is correct (the INI file is configured with warning, but you did not find it in the log file), it means that the current environment configuration will not generate warning, then let's go to the output buffer settings as described by felix021 upstairs.