opening a file (and closing it later) only if flag is set

In my program I have currently a piece of code that looks like this

 void foo()
 {
    // defining local variables

    for (long i =0; i<maxiterations; i++)
    {
       // here the core of the code is executed
       // for each iteration an object of a class is created and modified given the conditions imposed
    }

    if (flag) savedata();

    // and here a call to the destructor of the class is called (tested, it destroys all the previously created objects)

 }

Currently savedata() is like the following

 void savedata()
 {
    char filenameI[1024];
    sprintf_s(filenameI, 1024, "%s_%i", filename, id);
    FILE* File;
    errno_t err;
    err = fopen_s(&File, filenameI, "w");
    if (err!=0)
    {
            cout << "\nFile" << filenameI << "could not be opened.\nPlease press Ctrl+C to terminate" << endl; // the program is run via Matlab
            cin.get();
    }
    else
    {
        cout << "Saving file " << filenameI << endl;
    }

    for (long i =0; i<maxiterations; i++)
    {
        fprintf(File, "%10li", data); //not the actual line, but fprintf is used in this way
    }

    fclose(File);

 }

Since maxiterations is a run-time set long and given the memory required to store a single object is significant (i.e. I need higher values, but I hit the memory limit), I was thinking of modifying the code in the following way:

 void foo()
 {
     // defining local variables
     if (flag) openfile();

     for (long i开发者_如何学Go =0; i<maxiterations; i++)
    {
         // executing the same as before
         if (flag) savedata(i); // obviously the function would be modified
    }

    if (flag) closefile();

 }

Now, finally, my question:

using the same kind of output call (a FILE* instead of a ofstream object), is it possible to achieve what I need?

My doubts arise from the fact that what's inside a loop has a scope only in that loop and thus I fear that the file could be closed when I exit the first if statement instead of when the closefile() is called.

Am I wrong?

Thanks to anyone who will help.

Federico

suggestion:

FILE* f = NULL;
if (flag) f = openfile();

 for (long i =0; i<maxiterations; i++)
    {
         // executing the same as before
         if (flag) savedata(i, f); // pass in filehandle, obviously the function would be modified
    }

    if (flag) closefile(f); //close file on handle passed.

This will eliminate extra checks:

void foo()
{
    // defining local variables
    if (flag)
    {
        openfile();
        for (long i = 0; i<maxiterations; i++)
        {
            // executing the same as before
            savedata(i); // obviously the function would be modified
        }
        closefile();
    }
}