可变参数模板 arguments 引用

Question

How can I make this template function variadic:

template <typename T>
void checkedAlloc(size_t count, T*& x) {
  x = new T[count]();
  if(nullptr == x){
    fprintf(stderr, "Error: not enough memory (%llux%llu bytes).\n\n", count, sizeof(T)); 
    exit(1);
  }
}
size_t *A; checkedAlloc(20, A);

so as to be able to do:

size_t *A, *B, *C; checkedAlloc(20, A, B, C);

?

Solutions:

C++17 : Dani

template <typename ...T>
void checkedAllocV(size_t count, T*& ...x) {
    ((checkedAlloc(count, x)), ...);
}

C++14 : mch

void checkedAlloc(size_t count) {}
template <typename T, class ... Ts>
void checkedAlloc(size_t count, T*& x, Ts&& ...args) {
  try { x = new T[count](); }
  catch (const std::bad_alloc) {
    fprintf(stderr, "Error allocating memory (%zux%zu bytes).\n", count, sizeof(T)); 
    exit(1);
  }
  checkedAlloc(count, args...);
}

Answer 1

template <typename ...T>
void checkedAllocV(size_t count, T*& ...x) {
    ((checkedAlloc(count, x)), ...);
}

Answer 2

The C++14 version: It handles 1 parameter and calls the function with 1 less parameter. Termination function, when there is only count left to break the recursion.

void checkedAlloc(size_t count) {}

template <typename T, class ... Ts>
void checkedAlloc(size_t count, T*& x, Ts&& ...args) {
  x = new T[count]();
  if(nullptr == x){
    fprintf(stderr, "Error: not enough memory (%zux%zu bytes).\n\n", count, sizeof(T)); 
    exit(1);
  }
  checkedAlloc(count, args...);
}

https://godbolt.org/z/16jjsb

Let's go through the call graph for this main function:

int main()
{
    MyClass *A;
    int *B;
    float *C;
    checkedAlloc(20, A, B, C);
    delete[] A;
    delete[] B;
    delete[] C; 
}

checkAlloc gets called with 4 parameters (20, A, B, C).
This call allocs 20 elements of type of A and calls checkAlloc with 3 parameters (20, B, C).
This call allocs 20 elements of type of B and calls checkAlloc with 2 parameters (20, C).
This call allocs 20 elements of type of C and calls checkAlloc with 1 parameter (20).
This call ends up in the non template function in line 1 and does nothing.