For example only and not the actual code:
stringstream ss;
ss << " world!";
string hello("Hello");
// insert hello to beginning of ss ??
Thanks for all the responses, I also found this code, which works:
ostringstream& insert( ostringstream& oss, const string& s )
{
streamsize pos = oss.tellp();
oss.str( s + oss.str() );
oss.seekp( pos + s.length() );
return oss;
}
You cannot do it without making at least one copy. One way:
std::stringstream ss;
ss << " world!";
const std::string &temp = ss.str();
ss.seekp(0);
ss << "Hello";
ss << temp;
This relies on the "most important const" to extend the lifetime of the temporary and avoid making an extra copy.
Or, simpler and possibly faster:
std::stringstream ss;
ss << " world!";
std::stringstream temp;
temp << "Hello";
temp << ss.rdbuf();
ss = std::move(temp); // or ss.swap(temp);
This borrows the rdbuf approach from this answer, since the interesting problem here is how to minimize copies.
seekp approach copies more data around, even with C++11 move semantics. Come to think of it, the simplest and fastest approach is probably just to create a new stringstream and swap (or std::move) the guts. I went ahead and edited my answer, which also should allow you to change your vote.the only way i can see is to create the string from stream and prefix your other string
string result = hello + ss.str();
its called a stream for a reason.
Assuming ss1 contains "hello"
ss1 << ss.rdbuf();
or
ss1 << "hello" << ss;
Refer this URL for more info:-
