reading / writing files

This is a discussion on reading / writing files within the C++ Programming forums, part of the General Programming Boards category; I've just started playing with file io. My raw data file contains the following: -52.387596 61.659180 -2.277227 -52.341648 61.521450 -2.243313 ...

  1. #1
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    reading / writing files

    I've just started playing with file io.

    My raw data file contains the following:

    -52.387596 61.659180 -2.277227
    -52.341648 61.521450 -2.243313
    .....

    and I want to output a file such

    #PSI Format 1.0
    #
    # column [0] = "x"
    # column [1] = "y"
    # column [2] = "z"
    # column [3] = "Energy"
    # column [4] = "Id"
    # type[3] = byte

    -52.3876 61.6592 -2.27723 0 0

    As you can see from numbers in my outputed file the numbers have been rounded.

    Q - How do I get around this?

    Heres my code

    Code:
    #include <iostream>
    #include <fstream>
    
    #include <stdio.h>
    
    using namespace std;
    
    
    int main (int argv, char* arvc[]){
    	
    	char *sourceFileName = "start.xyz";
    	char *destinationFileName = "finish.psi";
    
    	fstream finput;
    	fstream foutput;
    	
    
    	finput.open(sourceFileName, ios::in);
    	foutput.open(destinationFileName, ios::out);
    
    	int index = 0;
    	string line;
    	double
    		x, y, z;
    
    	if (finput.is_open() && foutput.is_open()){
    		
    		foutput << "#PSI Format 1.0" << endl;
    		foutput << "#" << endl;
    		foutput << "# column [0] = \"x\"" << endl;
    		foutput << "# column [1] = \"y\"" << endl;
    		foutput << "# column [2] = \"z\"" << endl;
    		foutput << "# column [3] = \"Energy\"" << endl;
    		foutput << "# column [4] = \"Id\"" << endl;
    		foutput << "# type[3] = byte" << endl;
    		foutput << "" << endl;
    
    		while (!finput.eof()){
    			
    			finput >> x >> y >> z;
    			foutput << x  << " " << y << " " << z << " " << 0 << " " << index << endl ;
    			index++;
    			
    		}
    			
    
    		foutput.close();
    		finput.close();
    
    
    
    	}else{
    		
    		cout << "Error in opening eithe input or output files";
    
    		if (finput.is_open ()){
    			finput.close();
    		}
    
    		if (foutput.is_open()){
    			foutput.close();
    		}
    
    	}
    
    
    	cout << "Conversion undertaken";
    	
    	cin.ignore();
    	cin.ignore ();
    	return 1;
    }
    Perhaps I'm missing something real silly. I tried to make x,y,z floats as well but this didnt work either :-(

    Thanks for pointers.

  2. #2
    Registered User manofsteel972's Avatar
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    i believe you need to include the <iomanip> header and use setprecision(n). the default precision is 6 digits.
    "Knowledge is proud that she knows so much; Wisdom is humble that she knows no more."
    -- Cowper

    Operating Systems=Slackware Linux 9.1,Windows 98/Xp
    Compilers=gcc 3.2.3, Visual C++ 6.0, DevC++(Mingw)

    You may teach a person from now until doom's day, but that person will only know what he learns himself.

    Now I know what doesn't work.

    A problem is understood by solving it, not by pondering it.

    For a bit of humor check out xkcd web comic http://xkcd.com/235/

  3. #3
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    As I'm a real novice could you show some code as to how I would use this please?

    I tried to use

    Code:
    finput.open(sourceFileName, ios::in);
    finput.precision(8);
    but I still have my number rounded. In fact cangin the precision doesnt seem to do anything to my inputed numbers.
    Ta
    Last edited by ozzy34; 09-29-2004 at 08:50 AM.

  4. #4
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    Code:
    #include <iomanip>
    setprecision(n);       // Where n is the number of digits it's rounded to

  5. #5
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    nope afriad that doesnt appear to do anything.

    Any other pointers?

  6. #6
    Registered User manofsteel972's Avatar
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    its been a bit but i think this should do it.

    Code:
    foutput.setf(ios::fixed);
    foutput<<setprecision(n)<<double;
    "Knowledge is proud that she knows so much; Wisdom is humble that she knows no more."
    -- Cowper

    Operating Systems=Slackware Linux 9.1,Windows 98/Xp
    Compilers=gcc 3.2.3, Visual C++ 6.0, DevC++(Mingw)

    You may teach a person from now until doom's day, but that person will only know what he learns himself.

    Now I know what doesn't work.

    A problem is understood by solving it, not by pondering it.

    For a bit of humor check out xkcd web comic http://xkcd.com/235/

  7. #7
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    Code:
    			foutput << setprecision(8) << x  << " " << y << " " << z << " " << 0 << " " << index << endl ;

  8. #8
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    Afraid that doesnt appear to do the job either.

  9. #9
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    Thanks for responses guys.

    However the issue at the moment is getting the correct numbers read in.

    As mentioned -52.387596 61.659180 -2.277227 is read in as

    -52.3876 61.6592 -2.27723

  10. #10
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    mm not sure whats going on. Just tried swoopies code.

    I use the following input

    -52.387596 61.659180 -2.277227
    -52.341648 61.521450 -2.243313
    -52.383675 61.594273 -2.273051
    -52.337238 61.465927 -2.241447
    -52.379589 61.535492 -2.273933
    -52.371269 61.574524 -2.207932
    -52.373951 61.478222 -2.279162

    in my outputted file I get

    # PSI Format 1.0
    #
    # column [0] = "x"
    # column [1] = "y"
    # column [2] = "z"
    # column [3] = "Energy"
    # column [4] = "Id"
    # type[3] = byte

    -52.387596 61.65918 -2.2772269 0 1
    -52.341648 61.52145 -2.2433131 0 2
    -52.383675 61.594273 -2.273051 0 3
    -52.337238 61.465927 -2.241447 0 4
    -52.379589 61.535492 -2.2739329 0 5
    -52.371269 61.574524 -2.207932 0 6
    -52.373951 61.478222 -2.2791619 0 7

    As you can see the numbers are not the same....
    Last edited by ozzy34; 09-29-2004 at 09:23 AM.

  11. #11
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    Here's my output file, making the one change above.
    Code:
    #PSI Format 1.0
    #
    # column [0] = "x"
    # column [1] = "y"
    # column [2] = "z"
    # column [3] = "Energy"
    # column [4] = "Id"
    # type[3] = byte
    
    -52.387596 61.65918 -2.277227 0 0
    -52.341648 61.52145 -2.243313 0 1
    -52.341648 61.52145 -2.243313 0 2

  12. #12
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    >So is there some rounding that goes on in the debugger? I have a watch on x, y, z and they are always rounded?

    I never use a debugger, maybe someone knows why the Debugger rounds.

  13. #13
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    Well, you can do this if you want 6 digits after the decimal:
    Code:
    			foutput << fixed << setprecision(6) << x  << " " << y << " " << z << " " << 0 << " " << index << endl ;

  14. #14
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    I believe it will print properly, as long as your input contains six digits or less after the decimal. Same technique as Manofsteel showed.

  15. #15
    Registered User manofsteel972's Avatar
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    Floating point numbers don't necessarily have an exact binary representaion so that is probably why you are losing some precision. If you need precision try a BinaryCoded Decimal library that will maintain the precision.

    [edit]
    Here is an MSDN article that explains.
    http://support.microsoft.com/default...NoWebContent=1
    Last edited by manofsteel972; 09-29-2004 at 09:39 AM.
    "Knowledge is proud that she knows so much; Wisdom is humble that she knows no more."
    -- Cowper

    Operating Systems=Slackware Linux 9.1,Windows 98/Xp
    Compilers=gcc 3.2.3, Visual C++ 6.0, DevC++(Mingw)

    You may teach a person from now until doom's day, but that person will only know what he learns himself.

    Now I know what doesn't work.

    A problem is understood by solving it, not by pondering it.

    For a bit of humor check out xkcd web comic http://xkcd.com/235/

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