#include <fstream>

void test(void)
{
    std::ifstream file1("1.txt",std::ios_base::in | std::ios_base::binary);
    std::ifstream file2("2.txt",std::ios_base::in | std::ios_base::binary);
    std::ifstream file3("3.txt",std::ios_base::in | std::ios_base::binary);
    std::ofstream filecomm("com.txt",std::ios_base::out | std::ios_base::binary);

    filecomm << file1.rdbuf();
    filecomm << file2.rdbuf();
    filecomm << file3.rdbuf();

    file1.close();
    file2.close();
    file3.close();
    filecomm.close();
}