Warning: Cannot modify header information - headers already sent in - wordpress after activating custom plugin

Warning: Cannot modify header information - headers already sent by

If you got error like this after activation a new custom plugin in wordpress then you can use

error_reporting(0);    // Turn off all error reporting
  
Include this statement in every file due to which you are getiing warning . You are done , no more errors now :)

But remember if you are a developer..... you are only hiding errors ... not solving them ...
Try to solve them first ... If unable only then use this :)