c++ - 如何在 C++ 中重写 cout？

Question

我有一个要求，我需要使用printf 和cout 将数据显示到控制台和文件 中。对于printf我做到了但是对于cout我很纠结，怎么办？

   #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!\n";
        int howbad = 10;

        printf(outfile, "\n--------\n");
        //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;
    }

我已经在COUT(大写，上面代码的注释部分)中完成了。但我想使用普通的 std::cout，所以我该如何覆盖它。它应该适用于 sting 和变量，比如

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

或者无论如何都可以捕获stdout 数据，以便它们也可以轻松写入文件和控制台。

Answer 1

如果你有另一个流缓冲区，你可以只替换 std::cout 的:

std::cout.rdbuf(some_other_rdbuf);

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