command line arguments

[evantri]

I am developing a program that prompt the input from the command line argument. For example, this is the lists of command line arguments that I want to include:

-fish
-cat
-dog
-animal

All command line arguments can be in any order, BUT -animal must be in the last command line argument otherwise error message displayed

Let's say this input at the command line (using cc compiler)

a.out -fish -dog -animal

That kind of input is valid, but for:

a.out -fish

a.out -fish -animal -dog

Those kinds of input are not valid because -animal is not at the last command line or it is missing

Can someone help me by giving the code please?

[tyreld]

You'd want something like this:

int i;
 
// Parse all the command line arguments except the very last one
for (i = 1; i < argc - 1; i++) {
   if (!strcmp(argv[i], "-fish")) {
      // do whatever
   } else if (!strcmp(argv[i], "-dog")) {
      // do whatever
   } else if (!strcmp(argv[i], "-cat")) {
      // do whatever
   } else {
      // bad option create error
   }
}
 
// Parse the final command line argument to make sure it is "-animal"
if (strcmp(argv[argc - 1], "-animal") {
   // generate error because final option isn't "-animal"
}
 

Keep in mind that "strcmp" returns 0 if the two strings match. Hence the reason I've used the ! operator in the if statements where you want to check for a match. Also, note that argv[0] is the name of the executable. So, we start checking arguments at argv[1].

[evantri]

You'd want something like this:

int i;
 
// Parse all the command line arguments except the very last one
for (i = 1; i < argc - 1; i++) {
   if (!strcmp(argv[i], "-fish")) {
      // do whatever
   } else if (!strcmp(argv[i], "-dog")) {
      // do whatever
   } else if (!strcmp(argv[i], "-cat")) {
      // do whatever
   } else {
      // bad option create error
   }
}
 
// Parse the final command line argument to make sure it is "-animal"
if (strcmp(argv[argc - 1], "-animal") {
   // generate error because final option isn't "-animal"
}
 

Keep in mind that "strcmp" returns 0 if the two strings match. Hence the reason I've used the ! operator in the if statements where you want to check for a match. Also, note that argv[0] is the name of the executable. So, we start checking arguments at argv[1].

so is it possible if I change the comparison in the FOR loop like this:

 
for (i = 1;i < argc - 1;i++)
        {
         if (!strcmp(argv[argc-1],"-fish") == 0)
                 {
                  // do ....
                 }
        if (!strcmp(argv[argc-1],"-dog") == 0)
                 {
                  // do ....
                 }
         }
if (strcmp(argv[argc-1],"-animal") == 0)
           {
            // do...
            }
else
        {
         //do bla bla bla
         }
 

[tyreld]

No. In each iteration of the loop you are always comparing the string at argv[argc - 1]. You need to change the 1 to "i" for this to actually iterate through the arguments list starting with the second to last element.

[jmftrindade]

You do not need the else if statements. You can just use continue:

   /* iterate over all arguments */
   for (i = 1; i < argc - 1; i++) {
       if (strcmp("-arg0", argv[i]) == 0) {
          // do something. maybe check what argv[++i] contains
          continue;
       }
       if (strcmp("-arg1", argv[i]) == 0) {
          // do something. if you want to exit if arg1 is not the last argument, then:
          if (i != (argc -1)) {
              /* some function that exits the program and prints the usage */
              return usageHelp();
          }
          continue;
       }
       if (strcmp("-arg2", argv[i]) == 0) {
          // do something
          continue;
       }
       /* some function that exits the program and prints the usage */
       return usageHelp();
   }

[jmftrindade]

I forgot to say something before. In your case, when -animal is found, you just need to check if this is the last argument. You can do it like this:

/* iterate over all arguments */
for (i = 1; i < argc - 1; i++) {
if (strcmp("-animal", argv[i]) == 0) {
// do something. maybe check what argv[++i] contains
if (i != (argc - 1)) {
// -animal is not the last argument. exit program with usage help
return usageHelp();
}
continue;
}
if (strcmp("-arg1", argv[i]) == 0) {
// do something
continue;
}
if (strcmp("-arg2", argv[i]) == 0) {
// do something
continue;
}
/* some function that exits the program and prints the usage */
return usageHelp();
}

You do not need the else if statements. You can just use continue:

   /* iterate over all arguments */
   for (i = 1; i < argc; i++) {
       if (strcmp("-arg0", argv[i]) == 0) {
          // do something. maybe check what argv[++i] contains
          continue;
       }
       if (strcmp("-arg1", argv[i]) == 0) {
          // do something
          continue;
       }
       if (strcmp("-arg2", argv[i]) == 0) {
          // do something
          continue;
       }
       /* some function that exits the program and prints the usage */
       return usageHelp();
   }

[MeeM]

anyone know how to expand on this code so that the last two args are filenames to be opened? bearing in mind that the switch args are optional, and the first filename is also optional, but the last one is compulsory.

so far i can check the optional args, and i can open one file cos it uses the last arg.... now i need it to check the second-last arg to see if its a filename (so no hyphen) and if it is, open it as well.