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Wrong example of using feof()
http://www.cplusplus.com/reference/clibrary/cstdio/feof/
This page contains the famous but wrong pattern of using feof() as the condition in a while loop. It also uses the %d conversion specifier to print a long int variable.
1. The printed file size is one larger than the real file size.
2. But even before printing the file size, the program invokes undefined behavior, so it is not even guaranteed that the output is wrong or correct. It could be anything.
Who is able to fix the example? Oh wait, when the example is fixed the call to feof() is no longer there, so the example would be unrelated to the topic. But maybe not, since lots of people use this pattern to copy files or read files. It should just be marked as clearly wrong.
(edit: oops, I overlooked the n - 1 at the end, which is somewhat surprising. The example also does not explain why you need to subtract one. So the example is only wrong in one place.)
This page contains the famous but wrong pattern of using feof() as the condition in a while loop. It also uses the %d conversion specifier to print a long int variable.
1. The printed file size is one larger than the real file size.
2. But even before printing the file size, the program invokes undefined behavior, so it is not even guaranteed that the output is wrong or correct. It could be anything.
Who is able to fix the example? Oh wait, when the example is fixed the call to feof() is no longer there, so the example would be unrelated to the topic. But maybe not, since lots of people use this pattern to copy files or read files. It should just be marked as clearly wrong.
(edit: oops, I overlooked the n - 1 at the end, which is somewhat surprising. The example also does not explain why you need to subtract one. So the example is only wrong in one place.)
Last edited on
I see what you mean.
I think we have to test the input received from fgetc. If it is EOF then we don't increment our count.
Unfortunately this would suggest that we didn't need the feof test in the while loop in the first place. We could have simply broken out of our loop when fgetc returned EOF.
I think we have to test the input received from fgetc. If it is EOF then we don't increment our count.
Unfortunately this would suggest that we didn't need the feof test in the while loop in the first place. We could have simply broken out of our loop when fgetc returned EOF.
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