how to use getopt

[tomtran43]

Here is my code:


#include <iostream>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

using namespace std;

int main(int argc, char **argv)
{
char *nvalue = "World";
int c=0;
int tvalue = -1;

while ((c = getopt (argc, argv, "nt:")) != -1)
switch(c)
{
case 'n':
nvalue = optarg;
break;
case 't':
tvalue = atoi(optarg);
break;
}

for (int i = 0; i < tvalue; i++)
{
cout<<"["<<i+1<<"] Hello "<<nvalue<<"!\n";
}

return 0;
}



when I typed in cmd: ./hello -t 3 it should appear:
[1] Hello World!
[2] Hello World!
[3] Hello World!

and when type: ./hello -t 3 -n Bob it should appear:
[1] Hello Bob!
[2] Hello Bob!
[3] Hello Bob!

however, it is not working. any help please?

[JLBorges]

//while ((c = getopt (argc, argv, "nt:")) != -1)
while ((c = getopt (argc, argv, "n:t:")) != -1)

And check if optarg is a null pointer.

[tomtran43]

It worked well if i type ./hello -t 3. But if i add -n bob, it doesnt work

[JLBorges]

Repeat: not "nt:", but "n:t:" (colon after n and after t)

[tomtran43]

I did change it and it is still now working

[JLBorges]

#include <iostream>
#include <unistd.h>
#include <cstdlib>

int main( int argc, char* argv[] )
{
    const char* nvalue = "World" ; 
    int tvalue = 1 ;
    
    int c ;
    while( ( c = getopt (argc, argv, "n:t:") ) != -1 ) 
    {
        switch(c)
        {
            case 'n':
                if(optarg) nvalue = optarg;
                break;
            case 't':
                if(optarg) tvalue = std::atoi(optarg) ;
                break;
        }
    }
    
    for( int i = 0 ; i < tvalue; ++i )
       std::cout << '[' << i+1 << "] Hello " << nvalue << "!\n" ;
    std::cout << '\n' ;   
}

http://coliru.stacked-crooked.com/a/4c075ea24e1c1055

[tomtran43]

Thank you so much!

[dhayden]

And check if optarg is a null pointer.

When can optarg be null in this case? It can point to an empty string, but isn't the whole point of the colon to indicate that the argument is required?

[JLBorges]

> isn't the whole point of the colon to indicate that the argument is required?

Does that imply: one should not guard against there being an inadvertent typo (as in the code in the original post) while specifying optstring?
http://coliru.stacked-crooked.com/a/78e6b91012721970