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Reusing the algorithm in >> without modifying the class

 
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blrmaani
Guest
PostPosted: Tue Jul 20, 2004 7:55 am    Post subject: Reusing the algorithm in >> without modifying the class Reply with quote


I have a class ( part of a library which is not modifiable ).

class myclass
{
public:
myclass() { }
friend istream& operator>>(istream&, myclass&);
private:
int mydata_;
};

istream& operator>>(istream& is, myclass& myobj)
{
// some algorithm to parse the input string and
// store it in mydata_
}

Question:

I want to use 'myclass' class but I want to test it with a string as
a input so that the algorithm in >> is executed. I know that I can
do this:

main()
{
myclass myobj;

cin >> myobj;

}

But if I want to give a input in the form of a string, what changes
are required? I do not have control to modify the original class and
I do not want to repeat the algorithm in >>.

thanks in advance

blrmaani.

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Carl Barron
Guest
PostPosted: Tue Jul 20, 2004 6:24 pm    Post subject: Re: Reusing the algorithm in >> without modifying the class Reply with quote


In article <15dfd9f3.0407191355.7db46450 (AT) posting (DOT) google.com>, blrmaani
<blrmaani (AT) yahoo (DOT) com> wrote:

Quote:
Question:

I want to use 'myclass' class but I want to test it with a string as
a input so that the algorithm in >> is executed. I know that I can
do this:

main()
{
myclass myobj;

cin >> myobj;

}

But if I want to give a input in the form of a string, what changes
are required? I do not have control to modify the original class and
I do not want to repeat the algorithm in >>.


use an std::istringstream, like this:


#include <sstream>
#include <string>
using namespace std;

int main()
{
myclass mydata;
string a(...);
istringstream in(a);
in >> mydata;
// ...
}

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Ulrich Eckhardt
Guest
PostPosted: Tue Jul 20, 2004 6:24 pm    Post subject: Re: Reusing the algorithm in >> without modifying the class Reply with quote


blrmaani wrote:
Quote:
class myclass
{
public:
myclass() { }
friend istream& operator>>(istream&, myclass&);
private:
int mydata_;
};

istream& operator>>(istream& is, myclass& myobj)
{
// some algorithm to parse the input string and
// store it in mydata_
}

Question:

I want to use 'myclass' class but I want to test it with a string as
a input so that the algorithm in >> is executed.

You are looking for stringstreams, see <sstream>.

Uli


--
FAQ: http://parashift.com/c++-faq-lite/

/* bittersweet C++ */
default: break;

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Maciej Sobczak
Guest
PostPosted: Tue Jul 20, 2004 9:25 pm    Post subject: Re: Reusing the algorithm in >> without modifying the class Reply with quote
Hi,

blrmaani wrote:

Quote:
I want to use 'myclass' class but I want to test it with a string as
a input so that the algorithm in >> is executed. I know that I can
do this:

main()
{
myclass myobj;

cin >> myobj;

}

But if I want to give a input in the form of a string, what changes
are required? I do not have control to modify the original class and
I do not want to repeat the algorithm in >>.

Luckily, you do not have to perform any changes in the original code.
This is a Good Thing and is a result of the IOStream library design.
You can substitute just about anything that provides the istream
interface; istringstream is a good candidate when in-memory strings are
needed:

#include <sstream>

int main()
{
std::istringstream ss("some string that you want to test");
myclass myobj;
ss >> myobj;
}

That's all, but look into your docs to see what other members
istringstream has - they may be useful.

This way, you can not only reuse the algorithm, but you can use this
technique to write *automatic* tests for your own algorithms.
Substituting istringstream with prepared input, and possibly retrieving
the results with ostringstream (if your algorithm produces results to
ostream&) can be a very good idea in such tests.

--
Maciej Sobczak : http://www.msobczak.com/
Programming : http://www.msobczak.com/prog/


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Sven Rosiers
Guest
PostPosted: Tue Jul 20, 2004 9:27 pm    Post subject: Re: Reusing the algorithm in >> without modifying the class Reply with quote
blrmaani wrote:

Quote:
I have a class ( part of a library which is not modifiable ).

class myclass
[SNIP]

Question:

I want to use 'myclass' class but I want to test it with a string as
a input so that the algorithm in >> is executed. I know that I can
do this:

main()
{
myclass myobj;

cin >> myobj;

}

But if I want to give a input in the form of a string, what changes
are required? I do not have control to modify the original class and
I do not want to repeat the algorithm in >>.


stringstream to the rescue!

#include <sstream>

int main() {
myclass myobj;
istringstream input("blablabla");

input >> myobj;
}


Regards,

Sven R.

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dietmar_kuehl@yahoo.com
Guest
PostPosted: Wed Jul 21, 2004 11:51 am    Post subject: Re: Reusing the algorithm in >> without modifying the class Reply with quote
Hi,
blrmaani wrote:
Quote:
main()

BTW, there is no "implict int"-rule in C++, i.e. the above line
shall read

int main()

instead.

Quote:
{
myclass myobj;

cin >> myobj;

}

But if I want to give a input in the form of a string, what changes
are required?

You need to change the source of input to be a stream reading from
a string. The standard C++ library supports such a class in the
header <sstream>:

#include <sstream>
int main() {
myclass myobj;
std::istringstream stream("whatever");

stream >> myobj;
}
--
<mailto:dietmar_kuehl (AT) yahoo (DOT) com> <http://www.dietmar-kuehl.de/>
<http://www.contendix.com> - Software Development & Consulting


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