2017-12-03 20:47:07

by SF Markus Elfring

Subject: selftests: Testing a write attempt into a full file?

Hello,

I have constructed another demonstration program.


#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
FILE *f = fopen("/dev/full", "a");

if (!f)
goto report_failure;

{
int const c = 'X';

if (fputc(c, f) != c)
goto report_failure;
}

return EXIT_SUCCESS;

report_failure:
perror(__func__);
return errno;
}


I got the following result.

elfring@Sonne:~/Projekte/selftests> gcc-7 putc_into_full_file1.c && ./a.out; echo $?
0


Does such a simple test example need further software development considerations?

Regards,
Markus

2017-12-03 21:59:07

by walter harms

Subject: Re: selftests: Testing a write attempt into a full file?

Am 03.12.2017 21:46, schrieb SF Markus Elfring:
> Hello,
>
> I have constructed another demonstration program.
>
>
> #include <errno.h>
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(void)
> {
> FILE *f = fopen("/dev/full", "a");
>
> if (!f)
> goto report_failure;
>
> {
> int const c = 'X';
>
> if (fputc(c, f) != c)
> goto report_failure;
> }
>
Your test is broken, you are writing actualy into a buffer.
Adding setbuf(f,NULL) to disable buffering will return
main: No space left on device

Otherwise force the buffer to be fflush()ed and i it will also
report an error.

> return EXIT_SUCCESS;
>
> report_failure:
> perror(__func__);
from perror(3):
errno is undefined after a successful library call

so this may or may not return what you expect.

re,
wh
> return errno;
> }
>
>
> I got the following result.
>
> elfring@Sonne:~/Projekte/selftests> gcc-7 putc_into_full_file1.c && ./a.out; echo $?
> 0
>
>
> Does such a simple test example need further software development considerations?
>
> Regards,
> Markus
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