Simple Virtual Streams Example

SourcePro Core : Essential Tools Module User's Guide : Stream Classes : 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.