CODEWITHSUNDEEP
c++
user10121051
user10121051

Reputation: 147

Pointer to the temporary string

we have the following functions:

std::wstring f(const std::string& ref){
    return boost::locale::conv::utf_to_utf<wchar_t>(s);
}

const f2(LPCWSTR p){
// use p
}

Is it safe to call:

std::string s = "x";
f2(f(s).c_str());

My doubt is raised by the fact that f(s) returns a temporary object and f2 takes a pointer to it.

Dr. Memory points that it is "unaddressable access". When I replace it with:

std::string s = "x";
std::wstring s2 = f(s);
f2(s2.c_str());

Dr. Memory does not point "unaddressable access"

Upvotes: 3

Views: 130

Answers (2)

Sander De Dycker
Sander De Dycker

Reputation: 16243

The temporary will remain valid for the duration of the full expression f2(f(s).c_str()); - ie. that includes the f2 function call.

This assumes that f2 will not store the pointer to be used after the function ends.

Upvotes: 5

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170143

So long as f2 doesn't store the pointer for later use, it's all perfectly fine.

Any temporary created during the evaluation of a sub-expression, exists until the end of the complete expression it appears in. So f(s).c_str() will be a valid pointer for the duration of the call to f2.

Upvotes: 7

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