The horror! Scientific code and how not to read your arguments…

Over the years I have seen many, many examples of poor programming practise, usually kludges and quick fixes but today I saw the most horrible code for reading in command-line arguments in a C program ever. I just had to share the horror…

   if ( (argc-1) < 5 ) {
	[ Usage error response code removed]

   /* read in command-line arguments */
   numFiles = (argc-1) - 6;
   sscanf( argv[ numFiles+1 ], "%s", insFileName );
   sscanf( argv[ numFiles+2 ], "%s", outFileName );
   sscanf( argv[ numFiles+3 ], "%d", &outType );
   sscanf( argv[ numFiles+4 ], "%hd", &windowStartTimeCodeword0 );
   sscanf( argv[ numFiles+5 ], "%d", &newStartLine );
   sscanf( argv[ numFiles+6 ], "%d", &newEndLine);

Now, where can I start with this? Erm, I’m a bit dumbfounded actually.

Not only does the test for the incorrect number of arguments test for the wrong number but then it uses an index from the last value to reference the other values! Of course, this means that if the wrong numbers of arguments are given then the values are put into the wrong variables. Worse, that could be read from memory the process doesn’t own.

And there’s more.. it blindly sscanf()s them into variables.

Now, you may have seen that if one argument is left off the command line the input file now becomes the executable itself and the output file is actually the input data file. This is how this came to my attention. Trying to debug the program for a student it was found that it wasn’t reading the data correctly… and the data file was mysteriously emptied of its hundreds of megabytes of data each time the program was run. Oops!

So, dear readers, have any of you ever seen a worse command line parsing code segment?

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