CODEWITHSUNDEEP
c++ccommand-line-interface
ahab
ahab

Reputation: 373

Best practice for creating silent CLI option?

I have a program that writes occasional status updates, but I'm sure some will want it to run silently so I have provided a -s / --silent CLI option. What would be the best way to have my program abide by that parameter?

This method adds a global variable, and still executes the fprintf functions adding to the smell slightly.

FILE *outfile
if (silent) {
   *outfile = NULL;}
else {
   *outfile = stderr;}
fprintf (outfile, "This program can run silently");

This method also adds a global variable, and if statments littered throughout the code also adding to the smell.

if (!(silent)){
   fprintf (stdout, "This program can run silently");
}

Ternary operators with a global variable might be more elegant:

(silent) ? : fprintf(stdout, "This program can run silently");

Are there better practices than any of these methods? Are there shortcomings to any one that I'm not seeing?

Upvotes: 1

Views: 97

Answers (2)

MSalters
MSalters

Reputation: 180145

Since it's also tagged C++, I'd like to point out that you can replace the output buffer of std::cout by calling std::cout.rdbuf(newbuf). A "devnull buff" is trivial to implement.

Upvotes: 1

Jeremy Friesner
Jeremy Friesner

Reputation: 73294

As Don Shankin said in his comment, the most maintainable way to do it is by wrapping fprintf() in a function that implements your filtering logic, and then have your code call the wrapper function rather than calling fprintf() directly. That way you only have to implement the filtering logic in a single location and not all over the place. Here's a program that demonstrates the technique:

#include <stdio.h>
#include <stdarg.h>

bool silent = false;

void my_fprintf(FILE * outFile, const char * fmt, ...)
{
   if (silent == false)
   {
      va_list argsList;
      va_start(argsList, fmt);
      vfprintf(outFile, fmt, argsList);
      va_end(argsList);
   }
}

int main(int argc, char ** argv)
{
   my_fprintf(stdout, "Not silent now...\n");
   silent = true;
   my_fprintf(stdout, "But now I'm silent, so you won't see this!\n");
   silent = false;
   my_fprintf(stdout, "Silent is false again!\n");
   return 0;
}

... and here is the output from the program:

Not silent now...
Silent is false again!

Upvotes: 2

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