inserting int into file name using stringstream

Question

I am using c++ 98 (as that is what is installed on the university server). I am trying to save an output to a file. The filename has to be dice_N.dat where N is the number of rolls of the dice, which I have called n_trials. I have tried following the suggestions on inserting int variable in file name. When using the second suggestion I get the output N.dat. Here the snippet of my code which tries to do this:

    ostringstream fileNameStream("dice_");
    fileNameStream << n_trials << ".dat";
    string fileName = fileNameStream.str();  
    ofstream myfile;
    myfile.open(fileName.c_str());

I can't use to_string as this is not supported in c++ 98

You can create your own template <class T> std::string ToString(const T& x) { std::ostringstream ss; ss << x; return ss.str(); } — Neil Kirk
– Neil Kirk, Commented Oct 2, 2014 at 12:55

P0W · Accepted Answer · 2014-10-02 12:49:42Z

1

Use :

ostringstream fileNameStream("dice_", std::ios_base::ate);

Specifies stream open mode as ate

See here

answered Oct 2, 2014 at 12:49

P0W

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1 Comment

Neil Kirk Over a year ago

What is the reason for ate?

utnapistim · Accepted Answer · 2014-10-02 12:51:19Z

1

The problem appears because the std::stringstream overwrites the initial buffer.

Try this instead:

ostringstream fileNameStream;                    // let this be empty
fileNameStream << "dice_" << n_trials << ".dat"; // and pass "dice_" here
string fileName = fileNameStream.str();  
ofstream myfile;
myfile.open(fileName.c_str());

Alternately, you can create the ostringstream with std::ios::ate as a flag (ate tells the stream it should append at the end of the input (and then, you can still pass the "dice_" part in the constructor and it will not be overwritten).

answered Oct 2, 2014 at 12:51

utnapistim

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Comments

Neil Kirk · Accepted Answer · 2014-10-02 13:11:23Z

1

ostringstream ss;
ss << "dice_" << n << ".dat";
myfile.open(ss.str().c_str());

edited Oct 2, 2014 at 13:11

answered Oct 2, 2014 at 12:51

Neil Kirk

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1 Comment

James Kanze Over a year ago

That should be std::ostringstream, but otherwise, this is the route I would have taken. (I always construct std::ostringstream empty. Somehow, it seems more logical; an output stream doesn't have any content until you inject it.)

Cory Kramer · Accepted Answer · 2014-10-02 12:44:51Z

0

You can use std::to_string to create a std::string from the int, then concatenate.
In fact, I would just make the whole filename this way

std::string fileName = "dice_" + std::to_string(n_trials) + ".dat";

answered Oct 2, 2014 at 12:44

Cory Kramer

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1 Comment

thewire247 Over a year ago

Thanks for your response, I can't use 'to_string' as this is only supported in c++ 11 not 98.

leemes · Accepted Answer · 2014-10-02 12:51:05Z

0

Simply provide all three parts with the << operator, it is also more readable since you don't mix different syntaxes:

ostringstream fileNameStream;
fileNameStream << "dice_" << n_trials << ".dat";
//...

answered Oct 2, 2014 at 12:51

leemes

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Comments

Nejc Galof · Accepted Answer · 2014-10-02 12:54:53Z

0

Convert your int with boost:

boost::lexical_cast<std::string>(yourint) from boost/lexical_cast.hpp

answered Oct 2, 2014 at 12:54

Nejc Galof

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