ifstream problem

[Bernhard Hidding]

Hi there,
I want to read an ASCII file ("magnetfile.da t") consisting of doubles into
an array. The ASCII file looks like this:

1.0 1.0 1.0 0.5
2.0 1.0 1.0 0.4
usw.

My code:

double magnefield[200]; //this is the array
int i;

ifstream magnetic_field_ array;
magnetic_field_ array.open("mag netfile.dat");
for (i=0;i<20;i++)
{
magnetic_field_ array >> magnefield[i]; //should write 1.0 , 1.0, 1.0,
0.5 ... into the array
}
magnetic_field_ array.close();

I use g++ on SuSE 9.1. The executable runs, however, when I print out my
array magnefield, strange numbers appear. What is going wrong?
By the way: my file "magnetfile.dat " is in my working directory. However,
g++ does not give our an error message if I remove the file, so I am not
sure if the program finds the file after all. Might this be the problem?

Thanks for your help,
Bernhard

[John Harrison]

Re: ifstream problem


"Bernhard Hidding" <hidding@uni-duesseldorf.de> wrote in message
news:cn03qd$mea $1@news1.rz.uni-duesseldorf.de. ..[color=blue]
> Hi there,
> I want to read an ASCII file ("magnetfile.da t") consisting of doubles into
> an array. The ASCII file looks like this:
>
> 1.0 1.0 1.0 0.5
> 2.0 1.0 1.0 0.4
> usw.
>
> My code:
>
> double magnefield[200]; //this is the array
> int i;
>
> ifstream magnetic_field_ array;
> magnetic_field_ array.open("mag netfile.dat");
> for (i=0;i<20;i++)
> {
> magnetic_field_ array >> magnefield[i]; //should write 1.0 , 1.0, 1.0,
> 0.5 ... into the array
> }
> magnetic_field_ array.close();
>
> I use g++ on SuSE 9.1. The executable runs, however, when I print out my
> array magnefield, strange numbers appear. What is going wrong?
> By the way: my file "magnetfile.dat " is in my working directory. However,
> g++ does not give our an error message if I remove the file, so I am not
> sure if the program finds the file after all. Might this be the problem?[/color]

It probably is. You should test to see if you open the file successfully.

ifstream magnetic_field_ array("magnetfi le.dat");
if (!magnetic_fiel d_array.is_open ())
cerr << "could not open file\n";

It is your responsibility to print an error message if you cannot open a
file, not the compilers.

john