sized arrays as function parameter types in C++

Question

I am using templates for my struct like:

#pragma pack(push, 1)
template <typename T>
struct S
{
   T t;

   inline void Set(const T& val) { t = val; }
}
#pragma pack(pop)

T can be an float, int, short or char[10], char[1] or char[2] (and preferably any length would be great).

While the above seems to work quite nicely for the integral types, I'm having difficulty implementing the char[n] portion in that:

1. I need to use strncpy or memcpy instead of the assignment operator
2. Using the above, the compiler complains about the signature (const char[2]& val) and my calling it via s.Set("T").
3. The interface between S with integral and character types has to be same as it's generic code that is calling them (and it doesn't care what type they are).

Answer 1

You can define template specializations for T in the case of char[10] , etc. Do any issues remain when you do that? But as Mat has already noted, using a string is an approach worth considering.

#include <iostream>

#pragma pack(push, 1)
template <typename T>
struct S
{
   T t;

   inline void Set(const T& val) { std::cout << "general\n"; }
};

template <int len>
struct S<char[len]>
{
   char t[len];

   inline void Set(const std::string& val) { std::cout << "specialization\n"; }
};
#pragma pack(pop)

int main() {

    S<int> a;
    a.Set(10);

    S<char[20]> b;
    b.Set("turkey!");

    return 0;
}

http://codepad.org/X8YVuFja output:

general
specialization

Answer 2

Well, a partial specialization might do the trick:

template <typename T> struct S
{
  T x;
  void set(const T & y) { x = y; }
};

template <typename T, unsigned int N> struct S<T[N]>
{
  T x[N];
  void set(const T (&y)[N]) { std::copy(y, y + N, x); }
};

Usage:

S<char[10]> b;
char c[10] = "Hello";
b.set(c);

Answer 3

Works fine for me: http://codepad.org/03FSqZC6

#pragma pack(push, 1)
template <typename T>
struct S
{
   T t;

   inline void Set(const T& val) {}
};
#pragma pack(pop)

int main() {
    typedef char (carray)[10];  //do you have a line like this?
    S<carray> lhs;
    carray rhs = "HELLO";
    lhs.Set(rhs);
    return 0;
}

Most likely your problem is caused by using the incorrect array type. See my code for an example of a correct typedef.

EDIT:

I just realized this becomes a pain to call Set if you already have a std::string or dynamic array of any sort. Do the template specialization.