selftests: Testing a write attempt into a full file?

selftests: Testing a write attempt into a full file?

[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;
	}

	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

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

[walter harms]

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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