concatenate stringstream in c++

Question

How can I concatenate two stringstreams?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include "types.h"    

int main () {
    char dest[1020] = "you";
    char source[7] = "baby";
    stringstream a,b;
    a << source;
    b << dest;
    a << b; /*HERE NEED CONCATENATE*/
    cout << a << endl;
    cout << a.str() << endl;
    return 0;
}

The output is the following in both tries:

0xbf8cfd20
baby0xbf8cfddc

The desired output is babyyou.

jli · Accepted Answer · 2013-08-28 19:41:50Z

19

Should be:

b << dest;
a << b.str();

stringstream::str returns the underlying string in the stringstream.

edited Aug 28, 2013 at 19:41

user283145

answered Nov 22, 2011 at 18:24

jli

6,6432 gold badges31 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

jli Over a year ago

Of course as mentioned you don't need 2 stringstreams in this case, however I assumed that the given example is a trivial version of some more complex use case.

Den-Jason Over a year ago

This will create a copy of b's string data; I think the questioner may be looking for a way to avoid doing that.

Michael Krelin - hacker · Accepted Answer · 2011-11-22 18:27:03Z

10

Or

a << b.rdbuf();

provided that get pointer is on the beginning of the stream to avoid allocating yet another std::string for content.

answered Nov 22, 2011 at 18:27

Michael Krelin - hacker

144k25 gold badges200 silver badges177 bronze badges

Comments

sehe · Accepted Answer · 2011-11-22 18:26:43Z

6

More generically across iostreams:

std::istream is1, is2; // eg. (i)stringstream
std::ostream os;       // eg. (o)stringstream

os << is1.rdbuf();
os << is2.rdbuf();
os << std::flush;

This works for filestreams, std::cin etc. as well as for stringstream

answered Nov 22, 2011 at 18:26

sehe

400k49 gold badges474 silver badges671 bronze badges

Comments

Sarfaraz Nawaz · Accepted Answer · 2011-11-22 18:29:52Z

5

You don't need two instance of std::stringstream. One is enough for the purpose.

std::stringstream a;
a << source << dest;

std::string s = a.str(); //get the underlying string

answered Nov 22, 2011 at 18:29

Sarfaraz Nawaz

363k121 gold badges681 silver badges866 bronze badges

Comments

Mr Ed · Accepted Answer · 2013-06-14 07:29:19Z

The question was "how to concatenate STREAMS", the answers explained how to concatenate the contents of the streams. Here is a class which can be used to concatenate two istreams into one istream (file ConcatStreams.h):

class ConcatStreams
: public std::streambuf {
std::streambuf* sbuf1_;
std::streambuf* sbuf2_;
char*           buffer_;
int useBuf;
int bufSize;
public:
ConcatStreams(std::streambuf* sbuf1, std::streambuf* sbuf2)
    : bufSize(1024), sbuf1_(sbuf1), sbuf2_(sbuf2), buffer_(new char[bufSize]), useBuf(1) {
}
ConcatStreams(const ConcatStreams& orig);
virtual ~ConcatStreams() { delete[] this->buffer_; }
int underflow() {
    if (this->gptr() == this->egptr()) {
        // get data into buffer_, obtaining its input from
        // this->sbuf_; if necessary resize buffer
        // if no more characters are available, size == 0.
        std::streamsize size=0;
        if(useBuf==1) {
            size = this->sbuf1_->sgetn(this->buffer_, bufSize);
            if(!size) { useBuf++;}
        } 
        if(useBuf==2) {
            size = this->sbuf2_->sgetn(this->buffer_, bufSize);
            if(!size) { useBuf++;}
        }
        this->setg(this->buffer_, this->buffer_, this->buffer_ + size);
    }
    return this->gptr() == this->egptr()
         ? std::char_traits<char>::eof()
         : std::char_traits<char>::to_int_type(*this->gptr());
 }
};

To use it:

#include "ConcatStreams.h"
istringstream msgIn1("this is a stream.");
istringstream msgIn2("this is another stream.");
ConcatStreams cs(msgIn1.rdbuf(), msgIn2.rdbuf());
istream msgIn(&cs);
cout << "'" << msgIn.rdbuf() << "'" << endl;

Basically the class uses the streambuf's from the streams passed to it to create a new streambuf which first reads the first streambuf and then reads the second streambuf when finished with the first one.

This class is bugged (the initialization of bufSize comes after the use in constructing buffer_) and is generally unnecessarily low-level. Here's a c++17 version stackoverflow.com/a/49441066/85371

FailedDev · Accepted Answer · 2011-11-22 18:25:00Z

0

Just replace a << b with a << b.str()

answered Nov 22, 2011 at 18:25

FailedDev

27k9 gold badges56 silver badges74 bronze badges

Collectives™ on Stack Overflow

concatenate stringstream in c++

6 Answers 6

2 Comments

Comments

Comments

Comments

1 Comment

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

2 Comments

Comments

Comments

Comments

1 Comment

Comments

Linked

Related