Ad:

C++ Discussion Thread
Marked Solved
Views: 758

Jan 20th, 2009

Doing something stupid with stringstream

Expand Post »

I put together this little example to test my sanity, and it failed!

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>
 
using namespace std;
 
/* Example.txt
23
test
4.5
*/
 
int main(int argc, char *argv[])
{
	string Filename = argv[1];
	cout << "Filename: " << Filename << endl;
 
	int Integer;
	string String;	
	double Double;
 
	ifstream fin(Filename.c_str());
 
	string line;
	stringstream linestream;
 
	getline(fin, line);
	linestream.str("");
	linestream << line;
	linestream >> Integer;	
 
	getline(fin, line);
	linestream.str("");
	linestream << line;
	linestream >> String;
 
	getline(fin, line);
	linestream.str("");
	linestream << line;
	linestream >> Double;
 
	fin.close();
 
	cout << "Integer: " << Integer << endl;
	cout << "String: " << String << endl;
	cout << "Double: " << Double << endl;
 
	return 0;
}
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>

using namespace std;

/* Example.txt
23
test
4.5
*/

int main(int argc, char *argv[])
{
	string Filename = argv[1];
	cout << "Filename: " << Filename << endl;

	int Integer;
	string String;	
	double Double;

	ifstream fin(Filename.c_str());

	string line;
	stringstream linestream;
		
	getline(fin, line);
	linestream.str("");
	linestream << line;
	linestream >> Integer;	

	getline(fin, line);
	linestream.str("");
	linestream << line;
	linestream >> String;

	getline(fin, line);
	linestream.str("");
	linestream << line;
	linestream >> Double;

	fin.close();

	cout << "Integer: " << Integer << endl;
	cout << "String: " << String << endl;
	cout << "Double: " << Double << endl;
	
	return 0;
}

The output is

C++ Syntax (Toggle Plain Text)
Filename: Example.txt
Integer: 65535
String: 
Double: 4.86439e-270
Filename: Example.txt
Integer: 65535
String: 
Double: 4.86439e-270

Can anyone spot the stupid bug?

Thanks,

Dave

Similar Threads

Need help for linked list in C++
Help!!!! Filtering A Text File in C++

daviddoria

Featured Poster

Reputation Points: 437

Solved Threads: 204

Posting Virtuoso

Offline

1,968 posts
since Feb 2008

Permalink

Jan 20th, 2009

Re: Doing something stupid with stringstream

A stringstream is still a stream. When you read to end-of-file, you need to clear the state before you can do anything substantial with the stream again:

C++ Syntax (Toggle Plain Text)
linestream.clear();
linestream << line;
...
linestream.clear();
linestream << line;
...

Narue

Administrator

Reputation Points: 6442

Solved Threads: 1393

Bad Cop

Offline

11,807 posts
since Sep 2004

Permalink

Jan 20th, 2009

Re: Doing something stupid with stringstream

That's what I thought I was doing with

C++ Syntax (Toggle Plain Text)
linestream.str("");
linestream.str("");

But I changed all of those to

C++ Syntax (Toggle Plain Text)
linestream.clear()
linestream.clear()

And I get the same garbage results.

Dave

daviddoria

Featured Poster

Reputation Points: 437

Solved Threads: 204

Posting Virtuoso

Offline

1,968 posts
since Feb 2008

Permalink

Jan 20th, 2009

Re: Doing something stupid with stringstream

I get correct results with the following code. The only changes were the ones you claim to have made:

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>
 
using namespace std;
 
/* Example.txt
23
test
4.5
*/
 
int main(int argc, char *argv[])
{
	string Filename = argv[1];
	cout << "Filename: " << Filename << endl;
 
	int Integer;
	string String;	
	double Double;
 
	ifstream fin(Filename.c_str());
 
	string line;
	stringstream linestream;
 
	getline(fin, line);
	linestream << line;
	linestream >> Integer;	
 
	getline(fin, line);
	linestream.clear();
	linestream << line;
	linestream >> String;
 
	getline(fin, line);
	linestream.clear();
	linestream << line;
	linestream >> Double;
 
	fin.close();
 
	cout << "Integer: " << Integer << endl;
	cout << "String: " << String << endl;
	cout << "Double: " << Double << endl;
 
	return 0;
}
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <sstream>

using namespace std;

/* Example.txt
23
test
4.5
*/

int main(int argc, char *argv[])
{
	string Filename = argv[1];
	cout << "Filename: " << Filename << endl;

	int Integer;
	string String;	
	double Double;

	ifstream fin(Filename.c_str());

	string line;
	stringstream linestream;
		
	getline(fin, line);
	linestream << line;
	linestream >> Integer;	

	getline(fin, line);
	linestream.clear();
	linestream << line;
	linestream >> String;

	getline(fin, line);
	linestream.clear();
	linestream << line;
	linestream >> Double;

	fin.close();

	cout << "Integer: " << Integer << endl;
	cout << "String: " << String << endl;
	cout << "Double: " << Double << endl;
	
	return 0;
}

Narue

Administrator

Reputation Points: 6442

Solved Threads: 1393

Bad Cop

Offline

11,807 posts
since Sep 2004

Permalink

Jan 20th, 2009

Re: Doing something stupid with stringstream

Just tested it with the changes mentioned, and it works for me too.

mahlerfive

Reputation Points: 33

Solved Threads: 18

Junior Poster in Training

Offline

77 posts
since Aug 2008

Permalink

Jan 20th, 2009

Re: Doing something stupid with stringstream

haha OH NO! The file was in the wrong directory... it works now.

I didn't gaurd it with

C++ Syntax (Toggle Plain Text)
if(fin == NULL)
if(fin == NULL)

because it was just a toy example... but clearly I should have!

Sorry for the silly mistake.

Dave

daviddoria

Featured Poster

Reputation Points: 437

Solved Threads: 204

Posting Virtuoso

Offline

1,968 posts
since Feb 2008

Permalink

Jan 20th, 2009

Re: Doing something stupid with stringstream

I'd think about how to check if a file is really open

Freaky_Chris

Reputation Points: 325

Solved Threads: 118

Master Poster

Offline

702 posts
since Apr 2008

This thread is solved

Either the thread starter or a moderator has marked this thread as solved. You can most likely trust the responses and answers given. There is most likely no reason for any further responses to be posted here. If you have a related question, please start a new thread in this forum instead.

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C++ Forum Timeline: how can a "scanf" input be a character when printed?

Next Thread in C++ Forum Timeline: write file in Linux using Multithreading

DaniWeb Message

Cancel Changes

User Name
Password