P99_FOR in C++11

Question

I am using the P99_FOR macro defined in P99 in my C99 code in order to iterate over VA_ARGS. It works perfectly.

P99_FOR(NAME, N, OP, FUNC,...)

Now I want to migrate to C++11 and I was wondering if there is any macro similar to P99_FOR.

Here is my code in C99:

#ifndef __cplusplus

    #include "p99/p99.h"

    #undef P00_VASSIGN
    #define P00_VASSIGN(NAME, X, I) NAME[I] = X

    #define FOREACH(x, y, z, u, ...) P99_FOR(x, y, z, u, __VA_ARGS__);

#else

    #define FOREACH(x, y, z, u, ...) ???  // C++ equivalent

#endif

#define set_OCTET_STRING(type, numParams, ...) { \
        FOREACH(type, numParams, P00_SEP, P00_VASSIGN, __VA_ARGS__); \
}

For example set_OCTET_STRING(myVar->speed, 3, 34, 10, 11) will expand to:

myVar->speed[0] = 34; myVar->speed[1] = 10; myVar->speed[2] = 11;

Answer 1

You have a couple of ways to go. If you can get iterators to your data, you can use std::accumulate.

The example is taken from the docs:

#include <iostream>
#include <vector>
#include <numeric>
#include <string>
#include <functional>

int main()
{
    std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    int sum = std::accumulate(v.begin(), v.end(), 0);

    int product = std::accumulate(v.begin(), v.end(), 1, std::multiplies<int>());

    [...]
}

---

If your arguments are not iterateable, e.g. single variables on the stack, you have to built it on your own, using variardic templates:

#include <vector>
#include <numeric>
#include <functional>
#include <iostream>

template <class Func, class ReturnType, class... Args>
ReturnType P99_FOR(Func op, ReturnType initialValue, Args... args) {
    std::vector<ReturnType> values{args...};
    return std::accumulate(values.begin(), values.end(), initialValue, op);
}

template <class... Tags>
struct TagList {};
int main(int argc, char* argv[])
{
    int a = 4, b = 10, c = 21;

    // You can use predefined binary functions, that come in the <functional> header
    std::cout << "Sum:" << P99_FOR(std::plus<int>(), 0, a, b, c) << std::endl;
    std::cout << "Product:" << P99_FOR(std::multiplies<int>(), 1, a, b, c) << std::endl;

    // You can also define your own operation inplace with lambdas
    std::cout << "Lambda Sum:" << P99_FOR([](int left, int right){ return left + right;}, 0, a, b, c) << std::endl;

    return 0;
}