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Appending << and >> to a char *

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# 1  
Old 11-21-2012
Appending << and >> to a char *
I am writing a C++ function so I can pass a name and message

I will call as

Code:
pr_error(stream,3,"name","message");

hoping to get

Code:
<<name>>
message

However I am running into problems with my function shown below when trying to append ">>".

Code:
void pr_error (
  FILE*  stream,
  int    shift,
  const char*  name,
  const char*  msg
) {

  using namespace std;
  char*  s;

  s = const_cast<char *>(name);

  //strcat (s, ">>");

  //  strcpy (s, name);

  const char* cc = s;
//  strcat (name,">>");
  cout<<"Hello World"<< endl;
  const char*  format = "%*s\e[0;31m%s\e[0m\n";
//  fprintf (stream, format, shift, " ", s);
  fprintf (stream, format, shift, " ", msg);

}

# 2  
Old 11-21-2012
change the format specification to add << >> and let fprintf do the formatting:

Code:
const char*  format = "<<%*s>>\e[0;31m%s\e[0m\n";

I do not see the need for the escape sequences, especially if the output of the program gets redirected to a log. For example, you may get some crud on the screen users cannot read easily using an editor or whatever. In other words it presupposes (assumes) too much.
# 3  
Old 11-21-2012
I thought to put some color especially when errors occur. Is there a solution to the problem or the only way is to remove the escape sequences. Is there a way to know if the user is redirecting to a file?
# 4  
Old 11-21-2012
Yes, the isatty system call. It needs plain file descriptors, not FILE *, not iostream. STDOUT_FILENO is defined as 1. STDIN and STDERR are 0 and 2 respectively. Things like ls and grep use isatty to only print color output or columnar output to an interactive terminal.

Code:
#include <unistd.h>

int main(void)
{
        if(isatty(STDOUT_FILENO))
                fprintf(stderr, "stdout is a terminal\n");
        else  fprintf(stderr, "stdout is a file or non-terminal device\n");

        return(0);
}

# 5  
Old 11-22-2012
ls by default print columns of filenames, when the output is a pipe that behavior goes away.

When you make a general purpose program that can interface with pipes, redirection, etc. --- you normally call fstat on STDOUT_FILENO and isatty if you like, all of this to see if the destination is a pipe or whatever. isatty() is a convenience call, IMO.
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