Re: Suggested method for returning a string from a C program?

DFS <nospam@dfs.com> writes:

On 3/18/2025 10:05 PM, Keith Thompson wrote:

DFS <nospam@dfs.com> writes:

I'm doing these algorithm problems at
https://cses.fi/problemset/list/
>
For instance: Weird Algorithm
https://cses.fi/problemset/task/1068
>
My code works fine locally (prints the correct solution to the
console), but when I submit the .c file the auto-tester flags it with
'runtime error' and says the output is empty.
>
------------------------------------------------------------
// If n is even, divide it by two.
// If n is odd, multiply it by three and add one.
// Repeat until n is one.
// n = 3: output is 3 10 5 16 8 4 2 1
>
>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
>
int main(int argc, char *argv[])
{
     int n = atoi(argv[1]);
     int len = 0;
     char result[10000] = "";
     sprintf(result, "%d ", n);
>
     while(1) {
         if((n % 2) == 0)
             {n /= 2;}
         else
             {n = (n * 3) + 1;}
>
         if(n != 1)
             {
                 len = strlen(result);
                 sprintf(result + len, "%d ", n);
             }
         else
             break;
     }
>
     len = strlen(result);
     sprintf(result + len, "1 ");
     printf("%s\n",result);
>
     return 0;
}
------------------------------------------------------------

I don't see any problem with the code, and neither does gcc on
my system. 

>
It also compiles cleanly on theirs.
>
>

But the code you posted contains a number of NO-BREAK
SPACE characters (0xa0).  "clang -Wno-unicode-whitespace" accepts
those characters without complaint, and gives non-fatal warnings
without that option.  gcc treats them as a fatal error.

>
Those were probably added by one of our newsreaders.
>
Here's what it looks like on Notepad++ (showing end of line symbols)
>
https://imgur.com/DTX9fZG

OK, but are you *sure* they aren't in the original file?

When I view it in Notepad++, the NBSP characters look just like spaces.

Do you have something like `cat -A` or a hex dump that you can use to
examine the file?

What compiler are you using locally?

Try temporarily introducing a deliberate syntax error or #error
directive to see if the autotester shows you compiler error messages.
If it just says the output was empty, that's consistent with the
problem being bad characters in the source file.  (And it's a bug
or misfeature in the autotester if it doesn't distinguish between
a compilation failure and incorrect runtime output.)

A minor point: You print a trailing space.  I don't know whether
the auto-tester will accept that.

>
I removed that, and no such luck.

We won't know whether that's a problem as long as the autotester isn't
seeing any output.

Thanks for looking at it.

You're welcome.

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */