How Can You Access Public Members of a Templated Base Class in C ?

Public Member Invisibility in Templated Class Inheritance

Consider the following C code:

<code class="cpp">class CBase {
public:
    char Arr[32];
    int Fn1();
    int Fn2();
};

class CDerived : public CBase {
public:
    int FnSum();
};</code>

In this code, CDerived inherits the public members of CBase. However, if this code is templated, making Arr and the functions templated, the public members of CBase become invisible to CDerived.

Solutions

To address this issue, several solutions exist:

• Solution #1: Prefix all references to CBase members with CBase::, where BYTES is the template parameter.
• Solution #2: Prefix all references to CBase members with this->.
• Solution #3: Use the using statement in CDerived to declare all the needed CBase members.

Problem with Solutions

Solutions #1 and #2 require verbose additions to the code, leading to source bloat and repetition. Solution #4, disabling strict conformance, is not portable and breaks away from the C standard.

Improved Solution

To simplify the code, one can use macros to automate the using statement addition in Solution #3:

<code class="cpp">#define USING_CBASE(param) USING_ALL(CBase<param>, Arr, Fn1, Fn2, Fn3, Fn4, Fn5)

// In CDerived<BYTES>, in a `public:` section
USING_CBASE(BYTES);</code>

This macro will automatically generate the necessary using statements for all the members of CBase that are used in CDerived.

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