How to convert a #define in a template (variadic?)

问题

I've two macros and I desire to convert them in C++ templates. I've problems in understendig how to convert them.

Here are the two macros:

#define __MATRIX_GETVALUE(C,T,val,dim0...) \
    va_list vl; \
    va_start(vl,dim0); \
    C->setPositions(vl,dim0); va_end(vl);\
    val = *((T *)(m_values)+posInValueVector())

#define __MATRIX_SETVALUE(C,T,val,dim0...) \
    va_list vl; \
    va_start(vl,dim0); \
    C->setPositions(vl,dim0); va_end(vl);\
    *((T *)(m_values)+posInValueVector())=val

The two macros above are used in the software in my first answer to this question.

回答1:

With C++11 and variadic template you can get n-dimensional matrices easily with for example:

template<typename T, int ...rest>
struct matrix;

template<typename T, int n>
struct matrix<T, n> {
    T data[n];
    matrix() {
        for (int i=0; i<n; i++) {
            data[i] = T(0);
        }
    }
    T& operator[](int index) { return data[index]; }
};

template<typename T, int n, int ...rest>
struct matrix<T, n, rest...> {
    matrix<T, rest...> data[n];
    matrix<T, rest...>& operator[](int index) { return data[index]; }
};

that can be used with:

matrix<double, 10, 9, 4> m;
for (int i=0; i<10; i++) {
    for (int j=0; j<9; j++) {
        for (int k=0; k<4; k++) {
            m[i][j][k] = i + j*2.718 + k*3.1416;
        }
    }
}

without the problems of the horrible macros you have now:

• reserved names
• regular names injection
• multiple evaluation of arguments
• variadic C function calls
• use of matrix object state for "current position"

来源：https://stackoverflow.com/questions/30010444/how-to-convert-a-define-in-a-template-variadic