Why Does g Throw an 'undefined reference to typeinfo' Error During Linking?

Understanding the "g undefined reference to typeinfo" Error

The "undefined reference to typeinfo" error in g is often encountered when linking multiple compilation units. It indicates that the linker is unable to resolve a reference to the type information for a specific class.

This error can occur when a virtual function is declared in a header file but not defined in the corresponding source file. When a virtual function is declared without a definition, it is essentially declared as "external," meaning that its implementation is assumed to be provided elsewhere. However, if the function is never defined, the linker will fail to find its implementation during linking.

This type of error also resembles situations where an external variable is declared without a definition in one compilation unit and a pointer to it is used in another compilation unit. At link time, the linker cannot resolve the address of the undefined variable and generates the error.

To resolve this error, it is necessary to define the virtual function in the source file where it is declared. This provides the linker with the necessary implementation details to successfully resolve the reference to the type information.

By understanding the underlying reasons for this error, developers can effectively troubleshoot and ensure that their code is properly defined and compiled without undefined references.

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