Command line arguments reading for flags and file names in C

Question

Hello I have a project I'm doing and I need my program to run from the command line and be able to read flags and file names that will be used in the program.

This is my current code. It compiles without entering any flags. I don't think my GetArgs does anything. I had help with that part of the code.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 1024
#define IN 1 /* inside a word */ 
#define OUT 0 /* outside a word */
/* count lines, words, and characters in input */

int numInputArgs;
int idx;
void GetArgs (int argc, char **argv){

for (idx = 1; idx < 4;  idx++) {
    if (strcmp(argv[idx], "-c") == 0) {
        printf("Flag -c passed\n");
        break;
    }
    else if (strcmp(argv[idx], "-w") == 0) {
        printf("Flag -w passed\n");
        break;
    }
    else if (strcmp(argv[idx], "-l") == 0) {
        printf("Flag -l passed\n");
        break;
    }
    else if (strcmp(argv[idx], "-L") == 0) {
        printf("Flag -L passed\n");
        break;
    }
    else {
        printf("Error: unknown flag\n");
        exit(-1);
    }
}
 }// end GetArgs

void lineWordCount ( ) {

int c, nl, nw, nc, state;


    state = OUT; nl = nw = nc = 0; 
    while ((c = getchar()) != EOF) {
            ++nc;

        if (c == '\n')
            ++nl; 

        if (c == ' ' || c == '\n' || c == '\t')
            state = OUT; 

        else if (state == OUT) {
            state = IN; ++nw;
        } 
        printf("%d %d %d\n", nl, nw, nc);
    }
 }// end lineWordCount








 int main(int argc, char **argv){

GetArgs(argc, argv);
lineWordCount();
printf("Hello");

//fclose( src );
}

You're right, all GetArgs does is print the arguments. If you are on a POSIX machine (like Linux or Mac OSX) I suggest you look to getopt. There are also many arguments parsing libraries available if you search, the above mentioned getopt function exists for Windows as well for example. — Some programmer dude
– Some programmer dude, Commented Sep 18, 2012 at 5:48
Your GetArgs does perfectly what it should: $ gcc -o issue issue.c $ ./issue.exe a b c abc So, what exactly is your question? — Andreas Fester
– Andreas Fester, Commented Sep 18, 2012 at 5:50
I need the GetArgs to be able to scan for four potentially flags that decide what information is displayed at the end. before processing the files. — V Or
– V Or, Commented Sep 18, 2012 at 5:51

Andreas Fester · Accepted Answer · 2016-04-07 05:27:40Z

4

You can either use a standard function like getopt() as mentioned by @Joachim, if it is available on your system, or you can code it yourself. If you have a complicated command line syntax, getopt() might be better suited - if you only need to check for a limited set of flags, it might be easier to code it yourself, for example:

void GetArgs (int argc, char **argv){
   int idx = 0;

   for (idx = 1; idx < argc;  idx++) {
       if (strcmp(argv[idx], "-a") == 0) {
          printf("Flag -a passed\n");
       } else if (strcmp(argv[idx], "-b") == 0) {
          printf("Flag -b passed\n");
       } else if (strcmp(argv[idx], "-c") == 0) {
          printf("Flag -c passed\n");
       } else {
          printf("Error: unknown flag %s\n");
       }
    }
}

edited Apr 7, 2016 at 5:27

answered Sep 18, 2012 at 5:57

Andreas Fester

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8 Comments

V Or Over a year ago

Is there something wrong with my main.. It isn't printing anything else besides what's in lineWordCount

Andreas Fester Over a year ago

lineWordCount() is not called at all in your code above. I took your code and passed it to the compiler unmodified, and when I call the programm with several command line arguments it prints each of them, exactly what I would expect ...

V Or Over a year ago

I added it right under GetArgs in main and I'm getting stuck in the GetArgs. Trying to mess with it so it will get to lineWordCount. I'll update the code right now.

V Or Over a year ago

I figured out why. I was using UNIX built in "wc" (word count) and I thought it was my program functioning. :(

Andreas Fester Over a year ago

In the unix shell, always call your program with ./ prepended to avoid such issues. Also, avoid using existing names (you can check with which or where)

|

Claudi · Accepted Answer · 2012-09-18 06:02:43Z

0

I recommend you to use argtable2 library. I have used it for a long time and I think it is great. There are tutorials available to see how powerful and easy to use it is.

answered Sep 18, 2012 at 6:02

Claudi

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