[PATCH] D25255: Add a c_str() method to StringRef, similar to data() but asserting if the string isn't null terminated (NFC)

[Zachary Turner via llvm-commits]

How frequently would it need to be done at each callsite?  My concern is
just that it sounds like we're adding a potentially dangerous function to a
very generic and widely used API for the purposes of one client.  If you
make the function available, people are going to use it without
understanding the implications.  Another possibility is that if this all
takes place within a single common translation unit, you could write a
private function inside there that looks like this:

const char *Unsafe_cstr(StringRef S) {
  assert(strlen(S.data()) == S.size());
  return S.data();
}

That way the unsafe function is not exposed to general clients of StringRef?

On Tue, Oct 4, 2016 at 4:10 PM Mehdi Amini <mehdi.amini at apple.com> wrote:

> The use case is that MachineInstruction have operands, but the size of
> their operands is limited. Right now you have the space for one-pointer,
> but not for a StringRef. So if you create a MachineInstruction that takes a
> symbol name as an operand, we can only store the “const chat *” from the
> StringRef.
>
> So what you’re suggesting to do is roughly what I’m trying to achieve here
> as well, but instead of replicating the logic at each call sites, I try to
> abstract it behind the API.
>
>
> On Oct 4, 2016, at 3:56 PM, Zachary Turner <zturner at google.com> wrote:
>
> I'm not familiar with those cases, but could you do something like this:
>
> assert(strlen(s.data()) == s.size() && "Str is not null terminated!");
>
> at each call site?
>
>
> On Tue, Oct 4, 2016 at 3:48 PM Mehdi Amini <mehdi.amini at apple.com> wrote:
>
> Neat, I didn’t know this one!
>
> That does not solve cases like the round-trip StringRef -> MO -> StringRef
> though.
>
>
> On Oct 4, 2016, at 3:38 PM, Zachary Turner <zturner at google.com> wrote:
>
> Can you use %*s format specifier in those cases?
>
> printf("%*s", s.size(), s.data());
>
> On Tue, Oct 4, 2016 at 3:34 PM Mehdi AMINI <mehdi.amini at apple.com> wrote:
>
> mehdi_amini added a comment.
>
> In https://reviews.llvm.org/D25255#561566, @zturner wrote:
>
> > Not sure how I feel about this.  It's convenient, but it has potential
> for abuse.  Where did you run into issues porting code to `StringRef` that
> this solves?
>
>
> I ran into this with "printf" like API at some point, or with places that
> can't be converted to StringRef because of space constraint, like
> MachineOperand. So you're out of the IR and you have to use .data() to
> initialize the MO. Later you may construct a StringRef from this "const
> char *" again.
>
> >   I've done a lot of `StringRef` porting in LLDB by now, and I've always
> managed to find a solution to this.  Usually it involves trickling the
> `StringRef` changes down further
>
> Usually that's what I do, yes. The problem is when you reach some cases
> like above.
>
>
> https://reviews.llvm.org/D25255
>
>
>
>
>
>
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