Detect if stdin is a terminal or pipe in C/C++/Qt

#include <stdio.h>
#include <io.h>
...
if (isatty(fileno(stdin)))
    printf( "stdin is a terminaln" );
else
    printf( "stdin is a file or a pipen");

struct stat stats;
fstat(0, &stats);
if (S_ISCHR(stats.st_mode)) {
    // Looks like a tty, so we're in interactive mode.
} else if (S_ISFIFO(stats.st_mode)) {
    // Looks like a pipe, so we're in non-interactive mode.
}

#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main() {
  char tty[L_ctermid+1] = {0};
  ctermid(tty);
  cout << "ID: " << tty << 'n';
  int fd = ::open(tty, O_RDONLY);
  if (fd < 0) perror("Could not open terminal");
  else {
    cout << "Opened terminaln";
    struct termios term;
    int r = tcgetattr(fd, &term);
    if (r < 0) perror("Could not get attributes");
    else cout << "Got attributesn";
  }
  if (isatty(fileno(stdin))) cout << "Is a terminaln";
  else cout << "Is not a terminaln";
  struct stat stats;
  int r = fstat(fileno(stdin), &stats);
  if (r < 0) perror("fstat failed");
  else {
    if (S_ISCHR(stats.st_mode)) cout << "S_ISCHRn";
    else if (S_ISFIFO(stats.st_mode)) cout << "S_ISFIFOn";
    else if (S_ISREG(stats.st_mode)) cout << "S_ISREGn";
    else cout << "unknown stat moden";
  }
  return 0;
}

#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>
#include <iostream>
using namespace std;
int main() {
  char tty[L_ctermid+1] = {0};
  ctermid(tty);
  cout << "ID: " << tty << 'n';
  int fd = ::open(tty, O_RDONLY);
  if (fd < 0) perror("Could not open terminal");
  else {
    cout << "Opened terminaln";
    struct termios term;
    int r = tcgetattr(fd, &term);
    if (r < 0) perror("Could not get attributes");
    else cout << "Got attributesn";
  }
  if (isatty(fileno(stdin))) cout << "Is a terminaln";
  else cout << "Is not a terminaln";
  struct stat stats;
  int r = fstat(fileno(stdin), &stats);
  if (r < 0) perror("fstat failed");
  else {
    if (S_ISCHR(stats.st_mode)) cout << "S_ISCHRn";
    else if (S_ISFIFO(stats.st_mode)) cout << "S_ISFIFOn";
    else if (S_ISREG(stats.st_mode)) cout << "S_ISREGn";
    else cout << "unknown stat moden";
  }
  return 0;
}

/* Parse input from a file and execute it */

int
PyRun_AnyFileExFlags(FILE *fp, const char *filename, int closeit,
                     PyCompilerFlags *flags)
{
    if (filename == NULL)
        filename = "???";
    if (Py_FdIsInteractive(fp, filename)) {
        int err = PyRun_InteractiveLoopFlags(fp, filename, flags);

/*
 * The file descriptor fd is considered ``interactive'' if either
 *   a) isatty(fd) is TRUE, or
 *   b) the -i flag was given, and the filename associated with
 *      the descriptor is NULL or "<stdin>" or "???".
 */
int
Py_FdIsInteractive(FILE *fp, const char *filename)
{
    if (isatty((int)fileno(fp)))
        return 1;