重复符号错误——全局常量

问题描述

在类的头部，接口声明之外，我已经声明了全局常量:

In the header of the class, outside of interface declaration, I've declared global constants:

NSString * const gotFilePathNotification = @"gotFilePath";
NSString * const gotResultNotification = @"gotResultOfType";

gotResultNotification 仅在此类中使用(目前)，但我在另一个类实现中引用了 gotFilePathNotificaion.为此，我导入了这个标题.

gotResultNotification is used only in this class (yet), but I reference gotFilePathNotificaion in another class implementation. To do it, I import this header.

当我尝试编译时，我在此标头中收到有关 gotFilePathNotification 的重复符号链接器错误.为什么会这样?

When I try to compile, I get a duplicate symbol linker error about gotFilePathNotification in this header. Why does it happen?

推荐答案

您在文件范围内的两个不同编译单元中有两个同名标识符.这违反了一个定义规则.相反，您需要 -

You have two identifier(s) with same name across two different compilation unit(s) at file scope. This violates One Definition Rule. Instead you need to -

1. 在头文件中声明全局变量标记为具有外部链接.

1. Declare the global variables marking to have external linkage in a header file.

extern NSString * const gotFilePathNotification;

现在在仅一个源文件中提供定义.

Now provide the definition in only one source file.

NSString * const gotFilePathNotification = @"gotFilePath";

现在，无论您何时需要使用这些变量，请在源文件中包含标头.

Now where ever you need to use these variables, include the header in the source file.

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