File I/O operations

I/O from an ASCII file

Here is an exemple to show how simple it is to work with formated ASCII data files. The plan is to create a file containing different values of a double x and the corresponding sin(x). Then, we read this file and plot the data.

How to save an Array as an ASCII file?

Here is the first part of the code.

    Array<double> x;
    //  x contains 1000 values, ranging from 0 to 10
    x = dindgen(1000)/100;
    //  now, we save x and sin(x) in the file "sine.txt"
    write("sine.txt","x= "+x+" ,y= "+sin(x));

and now the file sine.txt contains:

    x= 0 ,y= 0
    x= 0.01 ,y= 0.00999983
    x= 0.02 ,y= 0.0199987
    ...
    

How to read from an ASCII file?

This code should read the file previously created.

    Array<double> x,y;
    Array<string> s;

    s = read("sine.txt");
    x = getField<double>(s,2);
    y = getField<double>(s,4);

    plot(x,y);

• The function read creates an Array of strings where each element correspond to a line of the file.
• The function getField extract a given field of an array of string. At that stage, fields are only delimited by the space character; "x=" is here the first field, the second is the value of x, the third is ",y=", etc... That's why we extract here the fields 2 and 4.

I/O with binary data

Using the IDIL binary format

Specification of the idil binary format

IDIL Binary file format (.idil file) for Arrays.

    -int: version, 0 at that stage
    -int: object type, 1 for Array,
    -int: element type
    -char[32]: name
    -char[256]: comments
    -int: element size (sizeof(T))
    -unsigned char: number of dimensions (usually six)
    -long[# of dim]: dimension of the array
    -data buffer