Question

[itit]

I have the following code:

/* The program convert lower case to upper case 
or upper case to lower case, according to the
name display in arg[0]*/
---------------------------------------------------------------------------------------------------------------
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>

int main(int argc, char **argv)
{
    int(*convcase[2])(int)={toupper,tolower};
    int func;
    int result = EXIT_SUCCESS;
    
    int ch;
    
    if(argc > 0)
    {
            if(toupper((unsigned char)argv[0][0])=='U')
            func=0;
            else
            func=1;
            
    while ((ch=getchar()!=EOF))
    {
          ch(*convcase[func])((unsigned char)ch);
          putchar(ch);
          }
            }
    
    else
    {
        fprintf(stderr,"Unknown name.\n");
        result=EXIT_FAILURE;
    }
    
    return (result);
}

---------------------------------------------------------------------------------------------------------------

Can someone advise what is the meaning of the following line, I do not understand it:

if(toupper((unsigned char)argv[0][0])=='U')

Thanks,
itit

[Salem]

So where did you copy/paste this code from?

It's hard to believe that you could come up with an array of function pointers, and then not know what that line is all about.

[itit]

of course I have copied it!!! I'm studying it, and do not understand this code segment. Hence, instead of preach me, try to help me (if you can...) or you cannot?

[CommonTater]

of course I have copied it!!! I'm studying it, and do not understand this code segment. Hence, instead of preach me, try to help me (if you can...) or you cannot?

Hint: Scoop and Poop coding is generally frowned upon because, for the most part it fails to educate and tends to cause more problems than it solves. However, in a situation where you have copied code to study it, it's to your best advantage to say so up front. Knowing whether you wrote it or not will change the nature of the answers you get quite significantly.

if(toupper((unsigned char)argv[0][0])=='U')

This line is converting the first character of the command line to an upper case character then testing if it is a capital U.

Actually that line most likely contains a mistake since argv[0] is program's command line, argv[1] is the first parameter.

[Clairvoyant1332]

Actually that line most likely contains a mistake since argv[0] is program's command line, argv[1] is the first parameter.

I'm inclined to believe it's intentional. The program will behave differently depending on if it's named "upper" or "lower" for example. I've seen OS commands that do something similar, where a command in /usr/bin has multiple hard links.

[CommonTater]

I'm inclined to believe it's intentional. The program will behave differently depending on if it's named "upper" or "lower" for example. I've seen OS commands that do something similar, where a command in /usr/bin has multiple hard links.

You don't see that --at least not in my experience-- on Windows systems... but yes I can see how that would work. More *nix wierdness...