This error message can spring up in a previously functional PHP script when the memory requirements exceed the default 8MB limit. Don’t fret, though, because this is an easy problem to overcome.To change the memory limit for one specific script by including a line such as this at the top of the script:
ini_set("memory_limit","12M");
The 12M sets the limit to 12 megabytes (12582912 bytes). If this doesn’t work, keep increasing the memory limit until your script fits or your server squeals for mercy.
You can also make this change permanently for all PHP scripts running on the server by adding a line like this to the server’s php.ini file:
memory_limit = 12M
Keep in mind that a huge memory limit is a poor substitute for good coding. A poorly written script may inefficiently squander memory which can cause severe problems for frequently executed scripts. However, some applications are run infrequently and require lots of memory like importing and processing a big data file.
如果是vps云主機，服務(wù)器用戶推薦大家采用第三種方法。
