Simple Virtual Streams Example

Essential Tools Module User's Guide
Rogue Wave web site: Home Page | Main Documentation Page

5.4 Simple Virtual Streams Example

Here is a simple example that exercises RWbostream and RWbistream through their respective abstract base classes, RWvostream and RWvistream:

#include <iostream>
#include <fstream>
#include <rw/bstream.h>
#include <rw/cstring.h>

void save (const RWCString& a, RWvostream& v)
{
    // Save to the virtual output stream
    v << a; 
}

RWCString recover(RWvistream& v)
{
    RWCString dupe;

    // Restore from the virtual input stream
    v >> dupe; 

    return dupe;
}

int main ()
{
    RWCString a("A string with\ttabs and a\nnewline.");
    RWCString b;

    {
        std::ofstream f("junk.dat", std::ios_base::out);    // 1
        RWbostream bostr(f);                                // 2
        save(a, bostr);
    }                                                       // 3

    {
        std::ifstream f ("junk.dat", std::ios_base::in);    // 4
        RWbistream bistr (f);                               // 5
        b = recover (bistr);                                // 6
    }

    std::cout << "String sent to stream as: " << std::endl
              << "\t" << a << std::endl;                    // 7

    std::cout << "String read from stream as: " << std::endl
              << "\t" << b << std::endl;

    return 0;
}

Program Output:

String sent to stream as: 
      A string with   tabs and a
newline.
String read from stream as: 
      A string with   tabs and a
newline.

The job of function save(const RWCString& a, RWvostream& v) is to save the string a to the virtual output stream v. Function recover(RWvistream&) restores the results. These functions do not know the ultimate format with which the string will be stored. Here are some additional comments on particular lines:

`//1`	On this line, a file output stream `f` is created for the file `junk.dat`.
`//2`	An *RWbostream* is created from `f`.
`//3`	Because this clause is enclosed in braces `{ ... }`, the destructor for `f` will be called here. This will cause the file to be closed.
`//4`	The file is reopened, this time for input.
`//5`	Now an *RWbistream* is created from it.
`//6`	The string is recovered from the file.
`//7`	Finally, both the original and recovered strings are printed for comparison.

You could simplify this program by using class fstream, which multiply inherits ofstream and ifstream, for both output and input. A seek to beginning-of-file would occur before reading the results back in. Since some early implementations of seekg() have not proven reliable, we chose not to use the simpler approach for this example.

The Rogue Wave name and logo, and SourcePro, are registered trademarks of Rogue Wave Software. All other trademarks are the property of their respective owners.
Provide feedback to Rogue Wave about its documentation.