CODEWITHSUNDEEP
c++stringstream
balaji
balaji

Reputation: 1125

How stringstream works?

I'm using stringstream type variable in my program. following is code snippet:

stringstream keyvalueStream;
keyvalueStream << // appending some string 

somefun(keyvalueStream.str().c_str()); // Passing the char*
keyvalueStream.str(std::string()); // clearing the content of this variable.

Does clearing the content of keyvalueStream affect the string that I will get in the somefun()?

Upvotes: 0

Views: 270

Answers (4)

Praetorian
Praetorian

Reputation: 109289

The answer to your question depends on what somefun does with the char const * you've passed to it, and not on whether or not you clear the contents of the stringstream.

stringstream::str returns an std::string object by value, so it's irrelevant whether you clear the stringstream contents later on or not.

In the expression

somefun(keyvalueStream.str().c_str());

the returned string object will be destroyed when the call to somefun returns. Hence, if somefun somehow stores the char const * for later use, you will have undefined behavior. If it operates on the argument however it needs to in the current function call, your code is safe.

Upvotes: 3

liaK
liaK

Reputation: 11648

Yes. It will.

However you shouldn't even call the c_str() once you get the underlying str. It is available till the end of the expression.

From cppreference,

Notes

The copy of the underlying string returned by str is a temporary object that will be destructed at the end of the expression, so directly calling c_str() on the result of str() (for example in auto *ptr = out.str().c_str();) results in a dangling pointer.

Upvotes: -1

Rajat
Rajat

Reputation: 487

No it wont affect what you have passed into somefun() already. stringstream::str() return by value so you get a copy of the data in your stream, not a reference to it.

Upvotes: 0

Martin G
Martin G

Reputation: 18139

When reaching keyvalueStream.str(std::string()); in your snippet somefun(keyvalueStream.str().c_str()); has already finished executing, so no. If that was your question.

Upvotes: 0

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