ifstream problem

[Bernhard Hidding]

Hi there,
I want to read an ASCII file ("magnetfile.dat") 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("magnetfile.dat");
for (i=0;i<20;i++)
{
magnetic_field_array >> magnefield; //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]

Hi there,
I want to read an ASCII file ("magnetfile.dat") 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("magnetfile.dat");
for (i=0;i<20;i++)
{
magnetic_field_array >> magnefield; //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?

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

ifstream magnetic_field_array("magnetfile.dat");
if (!magnetic_field_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