CI framework Cannotmodifyheaderinformation-headersalreadysentby

APHPErrorwasencounteredSeverity: WarningMessage: Cannotmodifyheaderinformation a php Error was encountered

Severity: Warning

Message: Cannot modify header information-headers already sent by (output started at/var/www/fbz/application/models/Content. php: 268)

Filename: helpers/url_helper.php

It seems that

$ Logsession = $ this-> session-> all_userdata ();

This sentence will not be reported

Reply content:

A php Error was encountered

Severity: Warning

Message: Cannot modify header information-headers already sent by (output started at/var/www/fbz/application/models/Content. php: 268)

Filename: helpers/url_helper.php

It seems that

$ Logsession = $ this-> session-> all_userdata ();

This sentence will not be reported

Because the output has been made before the session is used.
Is it because of the PHP file?> Enter with a space at the end
Or echo or print is used.