


Why Do I Get \'Undefined References\' When Using Static Class Members in C ?
Dec 11, 2024 am 03:07 AMUndefined References to Static Class Members
In C , static members defined within classes require proper handling to avoid compilation errors.
Reason for Undefined References
Static members, despite being declared within class definitions, are not automatically defined unless explicitly done elsewhere. This is because declarations differ from definitions in C . A declaration merely introduces the member, while a definition allocates memory and provides an initial value.
Example
Consider the following class with an undeclared static member:
class Example { static bool exampleStaticMember; };
Attempting to use exampleStaticMember without defining it will result in "undefined references" errors.
Definition Requirements
To resolve this issue, the static member must be explicitly defined, typically in the source file (.cpp) that contains the class definitions. The definition simply declares the member again with its data type and a semicolon (';').
bool Example::exampleStaticMember;
Special Cases
- Const Integral/Enumeration Static Members: These can be initialized within the class definition itself.
- Static Template Members: Static members of class templates require definition in the header file.
Other Static Usages
Note that the static keyword has different meanings when applied outside of classes:
- Static Objects in Functions: Declares an object that retains its value between function calls.
- Static Objects/Functions in Namespace Scope: Declares objects/functions with internal linkage.
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