What is the StringRef equivalent of NULL?

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#1

What is the StringRef equivalent of NULL?

Peter

#2

StringRef()

-Chris

#3

What is the StringRef equivalent of NULL?

StringRef()

-Chris

So why does StringRef(NULL) segfault?

Peter

#4

IIRC, because it calls strlen(NULL).

-Eli

#5

So why does StringRef(NULL) segfault?

IIRC, because it calls strlen(NULL).

To better phrase the question, why doesn't it check and return
StringRef() in that case?

Peter

#6

Because that constructor is specified to take a non-null pointer :). It is a hot method and doing the null check would be wasteful.

-Chris

#7

Because that constructor is specified to take a non-null pointer :). It is a hot method and doing the null check would be wasteful.

-Chris

In the vast majority of cases (static argument), that cost will be
eliminated by a decent optimizer. This makes converting functions that
accept NULL in their const char * args hard to convert. Ultimately
though, it's your choice.

Peter

#8

I guess the argument here is the same as for std::string, that users who never ever pass null pointers see it as wasteful to have a test for every call. If someone believes his code can contain null pointers, the check could be before calling the constructor.

This is C++'s "you don't pay for what you don't use", to the extreme.

Bo Persson

#9

If someone believes his code can contain null pointers, the check could be before calling the constructor.

The only exception is a copy constructor.

Consider this:
void foo(const char * bar) { ... }

I can convert it to this:
void foo(llvm::StringRef bar) { /* converted as needed */ ... }

Unless bar can be NULL, in which case I have to add set check too all
the callers (ugh!). To make matters worse, if I miss one, the program
still type-checks.

Peter

#10

You can get your checks with an extra overload

void foo(const char* bar)
{ bar == 0 ? foo(llvm::StringRef()) : foo(llvm::Stringref(bar)); }

That way the cost is payed when possibly needed, and not by everyone creating a StringRef.

Bo Persson