windows - How to override cout in C++?

Question

I have a requirement, I need to use printf and cout to display the data into console and file as well. For printf I have done it but for cout I am struggling, how to do it?

   #ifdef _MSC_VER
     #define GWEN_FNULL "NUL"
     #define va_copy(d,s) ((d) = (s))
         #else
         #define GWEN_FNULL "/dev/null"
        #endif
        #include <iostream>
        #include <fstream>

        using namespace std;
        void printf (FILE *  outfile, const char * format, ...) 
        {

            va_list ap1, ap2;
            int i = 5;
            va_start(ap1, format);
            va_copy(ap2, ap1);
            vprintf(format, ap1);
            vfprintf(outfile, format, ap2);
            va_end(ap2);
            va_end(ap1);
        }
    /*    void COUT(const char* fmt, ...)
        {
            ofstream out("output-file.txt");
            std::cout << "Cout to file";
            out << "Cout to file";
        }*/
        int main (int argc, char *argv[]) {

            FILE *outfile;
            char *mode = "a+";
            char outputFilename[] = "PRINT.log";
            outfile = fopen(outputFilename, mode);

            char bigfoot[] = "Hello 

World!
";
        int howbad = 10;

        printf(outfile, "
--------
");
        //myout();

        /* then i realized that i can't send the arguments to fn:PRINTs */
        printf(outfile, "%s %i",bigfoot, howbad); /* error here! I can't send bigfoot and howbad*/

        system("pause");
        return 0;
    }

I have done it in COUT(caps, the commented part for the code above) . But I want to use normal std::cout, so how can I override it. And it should work for both sting and variables like

int i = 5;
cout << "Hello world" << i <<endl;

Or are there anyway to capture stdout data, so that they can be easily written into file and console as well.

Answer 1

If you have another stream buffer, you can just replace std::cout's:

std::cout.rdbuf(some_other_rdbuf);

See http://en.cppreference.com/w/cpp/io/basic_ios/rdbuf.