PHP在C / C isset（）函数的对口++ [英] Counterpart of PHP's isset() in C/C++

问题描述

PHP有一个非常好的功能，使用isset（$ VARIABLENAME）。它检查是否$ VARIABLENAME在程序中已经定义或没有。

PHP has a very nice function, isset($variableName). It checks if $variableName is already defined in the program or not.

我们可以建立C / C类似的功能++（某种符号表的查找）？

Can we build similar feature for C/C++ (some kind of symbol table lookup)?

推荐答案

我是一个C ++的家伙，但我记得在PHP中使用isset是用来检查一个变量包含通过GET / POST请求的传入，当值（我敢肯定还有其他的用途，但是这是一个常见的​​一种，我相信）。

I'm a C++ guy, but I remember in PHP isset is used to check if a variable contains a value when passed in through a get/post request (I'm sure there are other uses, but that's a common one I believe).

您真的没有什么动态类型在C ++中。所以你不能突然使用你没有previously明确定义的变量名。真的是因为在C ++中未设置变量没有这样的事。

You don't really have dynamic typing in C++. So you can't suddenly use a variable name that you haven't previously explicitly defined. There really is no such thing as an "unset" variable in C++.

就算你说诠释变种;不要初始化，变量有一个值，通常是垃圾，但在PHP意义上，它仍然套。

Even if you say "int var;" and do not initialize it, the variable has a value, usually garbage, but it's still "set" in the PHP sense.

我想的关闭将是preprocessor的#IFDEF和的#ifndef只检查是否已经定义使用​​#define的变量。但在我的经验，这是主要用于省略或​​添加基于标志code。例如：

The closes I suppose would be the preprocessor's #ifdef and #ifndef which only checks to see if you've defined a variable using #define. But in my experience this is mostly used for omitting or adding code based on flags. For example:

// code code code
#ifdef DEBUG
// debug only code that will not be included in final product.
#endif
// more code more code

您可以使用#define以确定是否包含调试code现在定义DEBUG。

You can define DEBUG using #define to determine whether to include "DEBUG" code now.

也许讲一点有关你想与使用isset的C ++相当于会给你如何去这样做的C ++之路更好地知道该怎么做。

Perhaps telling a bit more about what you're trying to do with the C++ equivalent of isset will give you a better idea of how to go about doing it "The C++ Way".

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