最近遇到的一个bug，根据条件搜索出来的数据，用PHPExcel导出Excel，很奇葩的问题是：只有某一天的数据导出来报错：找不到文件...
百思不得其解，各个步骤数据都获取到了，可以打印出来，没有毛病，后来用fiddler监听，发现报了一个500的错误：PHP Fatal error: Uncaught exception 'PHPExcel_Calculation_Exception' ...
查了一波，大多是说导出的数据中有特殊符号 “=” 导致Excel把等号后面的当成公式处理，所以出错
可是，问题是数据太大，这个“=”也不好找
在stack overflow上找到了答案：引用一下
I'm guessing that one of the values retrieved from your database begins with an = sign, in which case PHPExcel will "guess" that it's supposed to be a formula and store it as such.
If you have values that begin with an = that aren't formulae, then you need to tell PHPExcel that it is a string and that it should be stored as such.
This behaviour is defined in the default cell binder (PHPExcel/Cell/DefaultValueBinder.php).
If you want to force PHPExcel to store these values as strings, then you can use the setCellValueExplicit() method (which defaults to enforcing a string)
Or you can write a custom value binder and apply that instead of the default value binder
用setCellValueExplicit()把所有的输出到Excel表格的数据强制转为字符串，问题就解决了
马克一下