Compiler error initializer element is not a compile-time constant

Question

When compiling this code  I get the error  initializer element is not a compile-time constant   Can anyone explain why    import  PreferencesController h    implementation PreferencesController  -  id init       self    super init       if  self               Initialization code here             return self      NSImage  imageSegment     NSImage alloc  initWithContentsOfFile    User asd jpg     error here

User · Answer

A global variable has to be initialized to a constant value, like 4 or 0.0 or @"constant string" or nil. A object constructor, such as init, does not return a constant value.

If you want to have a global variable, you should initialize it to nil and then return it using a class method:

NSImage *segment = nil;

+ (NSImage *)imageSegment
{
    if (segment == nil) segment = [[NSImage alloc] initWithContentsOfFile:@"/user/asd.jpg"];
    return segment;
}

User · Answer

Because you are asking the compiler to initialize a static variable with code that is inherently dynamic

User · Answer

You can certainly  define a macro as shown below  The compiler will replace  IMAGE SEGMENT  with its value before compilation  While you will achieve defining a global lookup for your array  it is not the same as a global variable  When the macro is expanded  it works just like inline code and so a new image is created each time  So if you are careful in where you use the macro  then you would have effectively achieved creating a global variable    define IMAGE SEGMENT   NSImage alloc  initWithContentsOfFile    User asd jpg      Then use it where you need it as shown below  Each time the below code is executed  a new object is created with a new memory pointer   imageSegment   IMAGE SEGMENT

User · Answer

The reason is that your are defining your imageSegment outside of a function in your source code  static variable    In such cases  the initialization cannot include execution of code  like calling a function or allocation a class  Initializer must be a constant whose value is known at compile time    You can then initialize your static variable inside of your init method  if you postpone its declaration to init

User · Answer

When you define a variable outside the scope of a function  that variable s value is actually written into your executable file  This means you can only use a constant value  Since you don t know everything about the runtime environment at compile time  which classes are available  what is their structure  etc    you cannot create objective c objects until runtime  with the exception of constant strings  which are given a specific structure and guaranteed to stay that way  What you should do is initialize the variable to nil and use  initialize to create your image  initialize is a class method which will be called before any other method is called on your class   Example   NSImage  imageSegment   nil     void initialize       if  imageSegment          imageSegment     NSImage alloc  initWithContentsOfFile    User asd jpg      -  id init         self    super init         if  self                   Initialization code here                 return self

[objective-c] Compiler error: "initializer element is not a compile-time constant"

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