意外的头部空白行或输出和Cookie设置问题

PHP setcookie() or PHP header(‘Location:’) Not Working – With SolutionThe setcookie() or header() functions of PHP does not work at all!

The PHP setcookie() and header() should be called before ANY browser output. If there are any echo or print calls, or any accidental whitespaces, those functions just won’t work. If it works on your localhost (strangely it does under some conditions!) but not on your server, check for the no-output-before-headers violations and fix them to get them working.

Explanation
HTTP headers should be sent before any HTTP content, else they will not work. The PHP header() function is used for sending standard as well as custom HTTP headers, so naturally they should be called before any browser output. setcookie() is a wrapper function to header(‘Set-Cookie:’), so ultimately it’s a header() call, so setcookie() too will not work if it’s called after any browser output.

Notes

The PHP header() function is used for sending standard as well as custom HTTP headers
header() should be called before any browser output
setcookie() should be called before any browser output
setcookie() is a wrapper function to header(‘Set-Cookie:’)
php-setcookie-or-php-headerlocation-not-working-with-solution.html">http://www.hacksparrow.com/php-setcookie-or-php-headerlocation-not-working-with-solution.html

额外提示:

这是为什么最好不要在PHP文件的末尾使用关闭符号

     <?php

        echo hello world;

     ?>

的原因，因为很可能在这个关闭行之外输入以外的空白行、空白符