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Stl string return by const reference vs. const char *

I have an STL string member variable in my class,

class A {
public:
   const char* getData1() const { return data.c_str());
   const string& getData2() const { return _data; }
private:
   string _data;
};

getData1()

vs. getData2()

which one is better?

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4 answers


Someone who returns a string reference is better suited for two options. If the string is modified internally, the previously returned string reference will be valid, but const char *

probably not.

Better than either of these choices might be to simply return by value.



std::string getData3() const { return data_; }

Also, I would suggest not prefixed variables with underscore and get rid of that operator using namespace std;

.

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Both are a little dangerous because your object might go out of scope or its memory might get freed. But you will still have a pointer or reference to one of its members.

If you really want to do this, it only depends on whether you want to access the string methods or not. There c_str()

const char*

may also be a memory to be freed from you.



If _data

not that big, maybe just return string

instead const string&

.

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I usually prefer getData2()

. const char*

returned by a method c_str()

can only be used as long as data

non-const methods are not called. After that, the content const char*

is undefined. By returning const char*

, you hide this problem. If the user of the class needs to use a C style string, he can call c_str()

himself on the returned one const string&

.

Here we also assume that the user getData2()

reasonably assumes that the returned reference will only be available to him as long as the class object A

is not destroyed.

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Refunds are const string&

better. If you need one const char*

, you can simply call getData2().c_str()

, which is almost identical to what it does getData1()

.

Remember std::string

better than strings const char*

because they preserve length, not null terminated. This means that if you want to get the length of that string, it strlen(getData1())

is an O (n) getData2().length()

operation , but it is an O (1) operation.

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