使用GCMathParser进行iphone开发
我正在尝试在我的 iPhone 应用程序中使用 GCMathParser。为了编译它，我将 #import 更改为 #import 并将 pi 替换为 M_PI 并成功编译了代码。
它基本上工作正常，但是当我输入错误的语法（例如 3.3.3 或 3.. ）时，我会得到语法错误，正如我所期望的那样。但是下次我解析一个非常简单的公式（例如 5 ）时，我仍然会遇到语法错误。我确保分配新实例以确保它开始新的，但我仍然明白。有人有同样的问题吗？
I am trying to use GCMathParser in my iPhone application. To compile it, I changed #import <Cocoa/Cocoa.h> to #import <UIKit/UIKit.h> and replaced pi with M_PI and successfully compiled the codes.
It works basically fine, but when I input wrong syntax like 3.3.3 or 3.. , I get syntax error as I am supposed to. But the next time I parse a very simple formula such as 5 , I still get syntax error for that. I made sure to allocate new instance to make sure it starts new, but still i get it. Does anyone have the same issue?
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GCMathParser中似乎存在错误；不过，还有一个办法。有一个固定模式：当将格式错误的表达式输入解析器时，会引发异常。之后，即使提供了格式良好的表达式，也会再次引发异常。关键点是对格式良好的表达式求值两次。首先检查是否引发异常；如果是，只需重新计算相同的表达式。第二次评估格式良好的表达式时，不会引发异常。瞧！There seems to be a bug in the
GCMathParser; however there is a way around. There is a fixed pattern : when a malformed expression is fed into the parser an exception is raised. Right after that even if a well formed expression is fed, the exception is raised again. The key point is to evaluate the well formed expression twice. First check if an exception was raised; if YES simply reevaluate the same expression. Upon evaluating the well formed expression the second time, exception is not raised.Voila!