C++でcatコマンド

#include <iostream>
#include <fstream>
#include <functional>

void write(const char* filename)
{
    std::ifstream file(filename);
    if(file.good())
    {
        std::cout << file.rdbuf();
    }
    else
    {
        std::cout << "CANNOT OPEN " << filename << '\n';
    }
}

int main(int argc, char* argv[])
{
    if(argc == 1)
    {
        std::cout << std::cin.rdbuf();
    }
    else
    {
        std::for_each(argv + 1, argv + argc, std::ptr_fun(write));
    }
    return 0;
}