stringstream str() vs rdbuf()->pubsetbuf()

hi,

I've been toying with this & it doesn't seem to work.

Code:

---

        std::vector<char> vbuffer(filesize);
        fHandle.read(&vbuffer[0],filesize);
        stringstream ssbuffer;
        ssbuffer.rdbuf()->pubsetbuf(&vbuffer[0],filesize); //<<issue.

---

When I go to read from ssbuffer nothing is extracted & gcount() returns 0. Wondering if I'm missing something with this & how it works.

So I've been tinkering with the following instead & wondering if I should expect any issues:

Code:

---

        std::vector<char> vbuffer(filesize);
        fHandle.read(&vbuffer[0],filesize);

        stringstream ssbuffer;
        ssbuffer.str(&vbuffer[0]);

---

Any feedback would be much appreciated,
thanks :)

The first example works fine for me

Code:

---

#include <string>
#include <iostream>
#include <sstream>
#include <iostream>
#include <vector>

using namespace std;

int main() {

    vector<char> cv {'k','u','r','t' };

    stringstream str;
    str.rdbuf()->pubsetbuf(&cv[0], 3); // intentionally set the size to only 3
                                        // to see if it works if the string is not 0-terminated
    char c;
    str.get( c );
    string val;
    cout << "reading 1 char with get()\n"
        << "'" << c << "' gcount=" << str.gcount() << endl
        << "reading the rest returns \"";
    str >> val;
    cout << val << "\"" << endl
        << "now gcount() is still supposed to be 1 because it should return\nthe count of the last unformatted input gcount="
        << str.gcount() << endl;
}

---

my output :

Code:

---

reading 1 char with get()
'k' gcount=1
reading the rest returns "ur"
now gcount() is still supposed to be 1 because it should return
the count of the last unformatted input gcount=1

---

The second example is the usual way to initialize the stringstream from a string.
But I guess there is a problem the way you did it.

Code:

---

ssbuffer.str(&vbuffer[0]);

---

you call str() with a string that is initialized from a const char *, but the data is possibly not 0-terminated.
Kurt

hi

thank you for the reply.
Problem I'm having is once I do following;

Code:

---

                        fHandle.open(lpszPathName, std::ios::out | std::ios::in | std::ios::binary);
                        std::stringstream ssbuffer;
                        std::vector<char> vbuffer(lfilesize);
                        fHandle.read(&vbuffer[0],lfilesize);
                        ssbuffer.rdbuf()->pubsetbuf(&vbuffer[0],lfilesize);

---

Any read or get on the stream only returns the first 4-5 bytes. After that I don't get anything and size() or length() on stream::str() returns 0. I've realised I get a similar issue using the stream if I do;

Code:

---

                ssbuffer.str(&vbuffer[0]);

---

File appears to be read in properly into the vector though.

Code:

---

                        char ch;
                        CString str;
                        for(int i =0;i<100;i++)
                        {
                                ch = vbuffer.at(i); //<<no problem.
                                //ssbuffer.get(ch); //<<issue
                                str.Format(L"char: %d\n",ch);
                                //str.Format(L"char: %c\n"ch); //<<produces a String too long or IO Error
                                TRACE(str);
                        }

---

File I'm reading in is in binary.
I'd rather not have to use vector to do what I need, would prefer to use stream. Any help would be appreciated.

this will initialize the stringstream with a string that stops at the first 0 character

Code:

---

ssbuffer.str(&vbuffer[0]);

---

you have to use

Code:

---

ssbuffer.str(string(&vbuffer[0], vbuffer.size());

---

Kurt

is there anyway to do this without copying?