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• the C type of data is superficial (usually) when asking about orthogonality, the key in the switch between a file name of type char* and a file stream of type FILE* is what the data is representing.
• Orthogonality and complexity are orthogonal components
• Orthogonality and compactness are orthogonal

Inspect the libanalytics

use the source, Luke!

It’s on github.

Setting k

Goal: allow the user to specify a value of k as a command line argument

$ ./wordfreq -k 10 < jump.txt

We will start simple and just expect that the first command line argument will be the value of k, i.e.

$ ./wordfreq 10 < jump.txt

recall that because the shell performs the redirection associated with < jump.txt it does not pass those characters along to the program. In the preceding example the wordfreq will “see” 2 command line arguments:

argv[0]: "./wordfreq"
argv[1]: "10"
argv[2]: NULL

converting char* to long int

$ man strtol

We prefer strtol over the older atoi because we can perform more robust error checking with strtol (in fact atoi can not detect the difference between a string of “0” and a string of “not even a number”, both will return the integer value 0). Let’s modify our program, making judicial use of trace code (printing to standard error) to see what’s going on.

#include <stdio.h>
#include <stdlib.h> /* for strtol */

#include <analytics.h>

int main(int argc, char *argv[]) {
    int nlimit=10;
    /* additional variable declarations */

    if (argc > 1) {
        /* will be true if the user has supplied at least 1 command line
        argument */
        fprintf(stderr, "argv[1]: %s\n", argv[1]);
        /* argv[1] is a string (char*), but nlimit is an int */
        nlimit = strtol(argv[1], NULL, 10);
        fprintf(stderr, "nlimit: %d\n", nlimit);
        return 0; /* for testing, ignore the rest of the code for now */
    }

    /* rest of the implementation */
}

Compile and run this with a few different command line arguments

$ ./wordfreq 10
$ ./wordfreq "not even a number"
$ ./wordfreq

This as far as we got in class

Flexibility via CLAs

Parsing command line options

$ man getopt