float divide(const float a, const float b) {
  return a / b;
}

template<typename T>
auto divide(const T a,const T b) {
  return a/b;
}

template<typename T>
auto divide(const T a,const T b) {
  return a/b;
}

int main()
{

  float a = divide(5.0,10.0); // a == 0.5

  float b = divide(5,10);     // b == 0.0

  printf("%lf %lf", a,b);

  getchar();
}

//入力が浮動小数点の時はそのまま返す
//それ以外の時はfloatを返す
template<typename T, bool isint>struct IsRealT;
template<typename T>struct IsRealT<T, true> { using type = T; };
template<typename T>struct IsRealT<T, false> { using type = float; };

//入力が整数ならfloatを返す
template<typename T>
struct RealIfInt {
	using type = typename IsRealT<T, std::is_floating_point<T>::value>::type;
};

template<typename T>
auto divide(const T a, const T b) {

  using realT = typename RealIfInt<T>::type;

  return static_cast<realT>(a) / static_cast<realT>(b);
}

int main()
{

  auto a = divide(5.0, 10.0); // a == 0.5

  auto b = divide(5, 10);     // b == 0.5

  printf("%lf %lf", a, b);

  getchar();
}

#include<array>

#include<cstring>

template<size_t SIZE>
class NByteData {
  std::array<unsigned char, SIZE> m_data;
public:
  using ThisT = NByteData<SIZE>;

  unsigned char* data() { return m_data.data(); }

  ThisT& operator=(const ThisT& t) {
    for (size_t i = 0; i < m_data.size(); i++) {
      m_data[i] = t.m_data[i];
    }
    return *this;
  }

  bool operator==(const ThisT& t)const {
    for (size_t i = 0; i < SIZE; i++) {
      if (m_data[i] != t.m_data[i])
        return false;
    }
    return true;
  }

  bool operator!=(const ThisT& t)const {
    return !this->operator==(t);
  }

  NByteData() {}

  NByteData(const ThisT& src) {
    this->operator=(src);
  }

  NByteData(std::initializer_list<unsigned char> inits) {
    unsigned char* p = m_data.data();
    for (auto uc : inits) {
      *p = uc;
      ++p;
    }
  }

};

#include <iostream>
#include<vector>

#pragma warning(disable:4996)

#include "NByteData.hpp"

// 3byte rgbの画素作成
NByteData<3> uc3rgb(
  unsigned char r, 
  unsigned char g, 
  unsigned char b) {

  return NByteData<3>({r,g,b});
}

void pnmP3_Write(const char* const fname, const int vmax, const int width, const int height, const unsigned char* const p);

int main()
{

  std::vector<NByteData<3> > rgb_ppm;

  int width = 255;
  int height = 30;
  rgb_ppm.resize(width*height);

  for (int y = 0; y < height; y++) {
    for (int x = 0; x < width; x++) {
      rgb_ppm[y*width+x] = uc3rgb(x, 0, 0);
    }
  }

  pnmP3_Write(R"(C:\data\rgb.ppm)", 255, width, height, rgb_ppm.begin()->data());

}