How Can I Determine if Standard Input (stdin) is a Terminal or a Pipe in C or C ?

Determining Terminal or Pipe Connection in C or C

When executing a program, it is often necessary to determine whether the standard input (stdin) is connected to a terminal or a pipe. This distinction is crucial for understanding the type of input the program is receiving and adjusting behavior accordingly.

Problem Analysis

As observed, "python" behaves differently depending on whether it is called from a terminal or through a pipe. This indicates that the program detects the presence or absence of a terminal connection.

C or C Detection Solution

In C or C , the function isatty can be used to determine whether the specified file descriptor refers to a terminal or not. It takes a file descriptor as an argument, which is typically fileno(stdin) for stdin.

Example Code

Here is an example of how to use isatty in C or C :

#include <stdio.h>
#include <io.h> // For _isatty and _fileno on Windows

int main() {
  if (isatty(fileno(stdin))) {
    printf("stdin is a terminal\n");
  } else {
    printf("stdin is a file or a pipe\n");
  }

  return 0;
}</io.h></stdio.h>

On Windows, the functions isatty and fileno are prefixed with underscores, so the code becomes:

#include <stdio.h>
#include <io.h>

int main() {
  if (_isatty(_fileno(stdin))) {
    printf("stdin is a terminal\n");
  } else {
    printf("stdin is a file or a pipe\n");
  }

  return 0;
}</io.h></stdio.h>

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