[LLVMdev] Little question about Stringref

[Jonathan Roelofs]

On 4/22/14, 9:55 AM, Hanbing Li wrote:
> Hi,
>
> I tried to get the name of function+loop, so I write a small function as following:
>
> StringRef getStringofFL(const Function * F, const Loop * L){
> StringRef sr;
> std::string s1 = F->getName();
> std::string s2 = L->getHeader()->getName();
> sr = s1+s2;
To answer your first question, the std::string created by operator+ here gets 
destroyed when it goes out of scope. The StringRef holds on to a pointer to the 
buffer that that string used to own, making this a classic use-after-free bug.
> return sr;
> }
>
>
> However, two questions came:
>
> 1, if I output sr like: errs() << sr; it's ok (for instance: mainfor.cond), but
> when I called this function and got the StringRef: StringRef s= getStringofFL(F,
> L); errs() << s; the result is: m\275[\377\177\000\0002\354\333\004\001,why?
>
> 2, I used the StringMap, and the StringRef got from the function getStringofFL
> as a key. Then I stored something into this StringMap, but I couldn't get it
> with the same function and loop. why?
>
>
>
> Thank you!
>
>
> Hanbing
>
>
>
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-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded