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

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

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.
Thanks for looking at it.