Re: C code block: no return values

[Eric Schulte <schulte.eric@gmail.com>]

Roger Mason <rmason@mun.ca> writes:

> Hello,
>
> I'm working through examples in "A Multi-Language Computing Environment for
> Literate Programming and Reproducible Research" by Shulte et al. J. 
> Stat. Software, 46/3, 2012.
>
> This example compiles but results are not returned to the Org-mode buffer:
> ========================================================
> #+name: cocktail.c
> #+begin_src C :noweb yes :tangle cocktail.c
> #include <stdio.h>
> <<cocktail-sort>>
> <<main>>
> #+end_src
>
> #+name: main
> #+begin_src C
> int main(int argc, char *argv[]) {
> int lst[argc-1];
> int i;
> for(i=1;i<argc;i++)
> lst[i-1] = atoi(argv[i]);
> sort(lst, argc-1);
> for(i=1;i<argc;i++)
> printf("%d ", lst[i-1]);
> printf("\n");
> }
> #+end_src
>
> #+name: cocktail-sort
> #+begin_src C :noweb yes
> void sort(int *a, unsigned int l)
> {
> int swapped = 0;
> int i;
> do {
> for(i=0; i < (l-1); i++) {
> <<swap>>
> }
> if ( swapped == 0 ) break;
> swapped = 0;
> for(i= l - 2; i >= 0; i--) {
> <<swap>>
> }
> } while(swapped > 0);
> }
> #+end_src
>
> #+name: swap
> #+begin_src C
> if ( a[i] > a[i+1] ) {
> int temp = a[i];
> a[i] = a[i+1];
> a[i+1] = temp;
> swapped = 1;
> }
> #+end_src
>
> #+call: cocktail.c[:cmdline 8 7 6 3 2 4 78]()
> ===========================================
>
> Running C-c on the "call" line above produces:
>
> ===============================
> #+RESULTS: cocktail.c[:cmdline 8 7 6 3 2 4 78]()
> ================================
>
> The answers should be here.  But they aren't.
>
> Thanks for any help.
>
> Roger
>

Hi Roger,

Since the publication of that paper, the code block execution engine has
begun checking the return value of the invoked program to ensure it
exits with success before parsing the output.  The C program in this
example actually returns the value of the final printf, which is
non-zero and looks like a return.

To get this example working with the latest version of Org-mode, one
needs to added a "return 0;" to the end of the last code block, yielding
the following.

#+name: main
#+begin_src C
int main(int argc, char *argv[]) {
int lst[argc-1];
int i;
for(i=1;i<argc;i++)
lst[i-1] = atoi(argv[i]);
sort(lst, argc-1);
for(i=1;i<argc;i++)
printf("%d ", lst[i-1]);
printf("\n");
return 0;
}
#+end_src

With this change the example works as expected on my system.

Org-mode should do a better job of alerting the user to the reason why
it is not returning a result.

Cheers,

-- 
Eric Schulte
http://cs.unm.edu/~eschulte