在目标C中访问给出链接器错误的全局变量 [英] Accesing global variable giving linker error in objective C

问题描述

我已经声明了一个全局变量，如下所示：

  extern NSString * name; 
 @interface viewcontrollerOne {} 
  

在实现文件中，我使用某种方法访问全局变量像

   - （void）someMethod 
 {
 name = @hello; 
} 
  

但是这给了链接器错误。

name，引用自：
- viewcontrollerOne.o中的[viewcontrollerOne someMethod]
ld：符号（s）找不到架构i386
clang：error：linker命令失败，退出代码1（使用-v查看调用）

解决方案

以下仅仅是一个声明：

  extern NSString * const name; //<<注意：这通常应该是const 
  

它声明有一个符号 NSString * 命名为 name 。它不会创建存储。

为此，您需要为 name 提供一个定义。为此，请将以下添加到.m 文件中：

  NSString * const name = @ 你好; 
  

---

如果您想在实例方法中设置它，如你的例子所示，那么你可以声明它：

MONFile.h

  extern NSString * name; 
  

定义它：

MONFile.m

  NSString * name = 0; 
  

然后你可以写 name = @hello; 在你的实例方法中。

I have declared a global variable like below

extern NSString *name;
@interface viewcontrollerOne{}

in implementation file i am accessing that global variable in some method like

-(void)someMethod
{
name = @"hello";
}

but this is giving linker error.

"name", referenced from: -[viewcontrollerOne someMethod] in viewcontrollerOne.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation)

解决方案

The following is merely a declaration:

extern NSString * const name; // << side note: this should typically be const

It declares there is a symbol of NSString* named name. It does not create storage.

To do that, you will need to provide a definition for name. To do this, add the following to your .m file:

NSString * const name = @"hello";

---

If you want to set it in an instance method, as seen in your example, then you can declare it:

MONFile.h

extern NSString * name;

Define it:

MONFile.m

NSString * name = 0;

then you can write name = @"hello"; in your instance method.

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