RE: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms

David Laight
2019-07-23T15:41:34Z

From: Rasmus Villemoes
> Sent: 23 July 2019 07:56
...
> > +/**
> > + * stracpy - Copy a C-string into an array of char
> > + * @to: Where to copy the string, must be an array of char and not a pointer
> > + * @from: String to copy, may be a pointer or const char array
> > + *
> > + * Helper for strscpy.
> > + * Copies a maximum of sizeof(@to) bytes of @from with %NUL termination.
> > + *
> > + * Returns:
> > + * * The number of characters copied (not including the trailing %NUL)
> > + * * -E2BIG if @to is a zero size array.
>
> Well, yes, but more importantly and generally: -E2BIG if the copy
> including %NUL didn't fit. [The zero size array thing could be made into
> a build bug for these stra* variants if one thinks that might actually
> occur in real code.]

Probably better is to return the size of the destination if the copy didn't fit
(zero if the buffer is zero length).
This allows code to do repeated:
offset += str*cpy(buf + offset, src, sizeof buf - offset);
and do a final check for overflow after all the copies.

The same is true for a snprintf()like function

David

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