Difference stringstream and ostringstream

Question

I was trying out the below snippet but it is not giving the desired output:

#include<iostream>
#include<sstream>
using namespace std;
void MyPrint(ostream& stream)
{
    cout<<stream.rdbuf()<< endl;
}
int main()
{
    stringstream ss;
    ss<<"hello there";
    MyPrint(ss);                //Prints fine

    ostringstream oss;
    oss<<"hello there";
    MyPrint(oss);               //Does not print anything
    getchar();
}

I am aware that the only possible differences between stringstream and ostringstream is that the later forces the direction and is a bit faster than stringstream.

Am I missing out on anything?

PS: A similar question was posted earlier but didn't get any answers.

score 25 · Accepted Answer · answered Aug 15 '13 at 11:06

std::stringstream and std::ostringstream pass different flags to the std::stringbuf. In particular, the std::stringbuf of an std::ostringstream does not support reading. And std::cout << stream.rdbuf() is a read operation on the streambuf.

The way to extract characters from an std::ostringstream is by using the std::ostringstream::str() function.

score 1 · Answer 2 · answered Aug 15 '13 at 11:10

stringstream shouldn't be thought of as a bidirectional implementation of ostringstream and istringstream. It is implemented as a derrived class of both ostringstream and istringstream, which is why it implements both input and output capabilities.

Choosing which one to use depends on what it is used for. If you only need to write data to it on a stream without being able to access the data via a stream, then an ostringstream is all you would need. However, if you want to implement bidirectional on something you provide to an API but restrict it, you can cast it:

stringstream ss;  // My bidirectional stream

ostringstream *p_os = &ss;  // Now an output stream to be passed to something only allowed to write to it.

int bytes = collectSomeData(p_oss);

Difference stringstream and ostringstream

2 Answers2