XE6如何检查UnicodeString是否为null? [英] XE6 How do you check if a UnicodeString is null?

问题描述

我正在使用C++ Builder XE6.我得到一个UnicodeString作为参数，我希望检查字符串是否设置为NULL，而不是空字符串.

I'm using C++ Builder XE6. I'm getting a UnicodeString as a parameter and I wish to check if the string is set to NULL, and not an empty string.

我尝试进行一些简单的比较，以查看参数是否为null，但似乎失败了.我正在使用==运算符，该运算符似乎不起作用，这使我认为它已超载.

I've tried to do some simple compares to see if the param is null, but seem to be failing. I'm using the == operator which doesn't seem to be working, which makes me think it is overloaded.

我尝试过:

if (searchString == NULL)

在调试器视图中，它在局部变量中显示{ NULL }的值.如果将变量添加到监视列表，则表明它具有"Data"的属性，该属性为NULL.

In the debugger view, it shows the value of { NULL } in the local variables. If I add the variable to the watch list, then it shows it has a property of "Data" which is NULL.

关于如何正确进行比较的任何想法?

Any ideas on how I can properly do the compare?

推荐答案

没有像UnicodeString的NULL值这样的东西.字符串是一系列字符，但是NULL是指针(好吧-实际上，它是一个计算为int 0的宏，但是如果编译器未将其用于指示空指针，支持nullptr).

There is no such thing as a NULL value for a UnicodeString. A string is a series of characters, but NULL is a pointer (well - actually it is a macro that evaluates to an int, 0, but it is supposed to be used to indicate null pointers if your compiler doesn't support nullptr).

在内部，UnicodeString的data成员在字符串为空时为NULL，而在字符串具有至少1个字符时为非NULL.

Internally, the data member of UnicodeString is NULL when the string is empty, and non-NULL when the string has at least 1 character.

要检查字符串是否为空，请使用IsEmpty()方法，该方法检查data成员是否为NULL.只有一个空状态.像某些语言一样，空"和空"之间没有区别.

To check if the string is empty, use the IsEmpty() method, which checks if the data member is NULL or not. There is only one empty state; there is no distinction between "empty" and "null" like some languages have.

在调试器中看到的值是UnicodeString的内部data成员，而不是UnicodeString界面的一部分.当您在调试器中看到NULL时，应将其视为空字符串.

The value you see in the debugger is the internal data member of UnicodeString, it is not a part of UnicodeString's interface. When you see NULL in the debugger, you should treat it as being an empty string.

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