In Mixing C and C++ Code in the Same Program the following example (slightly abbreviated here to the relevant parts) is given. Assume buf.h
contains the following:
struct buf {
char* data;
unsigned count;
};
// some declarations of existing C functions for handling buf...
It is then recommended to use
extern "C" {
#include "buf.h"
}
class mybuf : public buf {
public:
mybuf() : data(0), count(0) { }
// add new methods here (e.g. wrappers for existing C functions)...
};
in order to use the struct within C++ with added features.
However, this clearly will produce the following error:
error: class `mybuf' does not have any field named `data'
error: class `mybuf' does not have any field named `count'
The reasons for this are explained in How can I initialize base class member variables in derived class constructor?, C++: Initialization of inherited field, and Initialize parent's protected members with initialization list (C++).
Thus, I have the following two questions:
Update: Using aggregation initialization as suggested, i.e.,
mybuf() : buf{0, 0} {}
works, but requires C++11. I therefore add the following question:
Using C++03, is there a better way to achieve the desired outcome than using the following constructor?
mybuf() {
data = 0;
count = 0;
}
To initialize a class member variable, put the initialization code in a static initialization block, as the following section shows. To initialize an instance member variable, put the initialization code in a constructor.
There are two ways to initialize a class object: Using a parenthesized expression list. The compiler calls the constructor of the class using this list as the constructor's argument list. Using a single initialization value and the = operator.
An initializer specifies the initial value of a variable. You can initialize variables in these contexts: In the definition of a variable: C++ Copy. int i = 3; Point p1{ 1, 2 };
If you can use a c++11 compatible compiler then this would be a perfect use case for an initializer list using aggregate initialization.
mybuf() : buf{0, 0}
{}
One "correct" way, if your compiler is C++11 capable, is to use e.g.
mybuf() : buf{0, 0} {}
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