获取Tcl解释器的输出

我正在尝试获得Tcl解释器的输出，如回答这个问题所描述的Tcl C API:将嵌入式Tcl接口的stdout重定向到一个文件而不影响整个程序。而不是写入数据到文件，我需要得到它使用管道。我将Tcl_OpenFileChannel更改为Tcl_MakeFileChannel，并将管道的写端传递给它。然后我做空了Tcl_Eval和一些看跌期权。管道读端没有数据。

#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <tcl.h>
#include <iostream>
int main() {
    int pfd[2];
    if (pipe(pfd) == -1) { perror("pipe"); exit(EXIT_FAILURE); }
/*
        int saved_flags = fcntl(pfd[0], F_GETFL);
        fcntl(pfd[0], F_SETFL, saved_flags | O_NONBLOCK);
*/
        Tcl_Interp *interp = Tcl_CreateInterp(); 
        Tcl_Channel chan;
        int rc;
        int fd;
        /* Get the channel bound to stdout.
         * Initialize the standard channels as a byproduct
         * if this wasn't already done. */
        chan = Tcl_GetChannel(interp, "stdout", NULL);
        if (chan == NULL) {
                return TCL_ERROR;
        }
        /* Duplicate the descriptor used for stdout. */
        fd = dup(1);
        if (fd == -1) {
                perror("Failed to duplicate stdout");
                return TCL_ERROR;
        }
        /* Close stdout channel.
         * As a byproduct, this closes the FD 1, we've just cloned. */
        rc = Tcl_UnregisterChannel(interp, chan);
        if (rc != TCL_OK)
                return rc;
        /* Duplicate our saved stdout descriptor back.
         * dup() semantics are such that if it doesn't fail,
         * we get FD 1 back. */
        rc = dup(fd);
        if (rc == -1) {
                perror("Failed to reopen stdout");
                return TCL_ERROR;
        }
        /* Get rid of the cloned FD. */
        rc = close(fd);
        if (rc == -1) {
                perror("Failed to close the cloned FD");
                return TCL_ERROR;
        }
        chan = Tcl_MakeFileChannel((void*)pfd[1], TCL_WRITABLE | TCL_READABLE);
        if (chan == NULL)
                return TCL_ERROR;
        /* Since stdout channel does not exist in the interp,
         * this call will make our file channel the new stdout. */
        Tcl_RegisterChannel(interp, chan);

        rc = Tcl_Eval(interp, "puts test");
        if (rc != TCL_OK) {
                fputs("Failed to eval", stderr);
                return 2;
        }
        char buf;
        while (read(pfd[0], &buf, 1) > 0) {
            std::cout << buf;
        }
}