Question

In C++, istream& operator>> can be used to read data “as in text”. What is the equivalent in D?

My attempt:

input.txt

c 1033
90.432

input_test.d

import std.stdio;
import std.stream;

void main()
{
    auto inputFile = new BufferedFile("input.txt");
    char c;
    int i;
    double d;

    inputFile.read(c);
    inputFile.read(i);
    inputFile.read(d);
    writeln(c, '\t', i, '\t', d);
}

Output

c   858796320   4.90559e-62

Answer 1

D has lots of ways of reading data from files to make various use cases convenient. Here are some:

• std.file.read for reading the contents of a file into an untyped array of bytes.
• std.file.readText for reading the contents of a file into a string.
• The members of the InputStream interface which you’ve already discovered.
• std.stdio.file:readln for reading lines from a file. Also see readf in the same structure.
• std.stdio.file:byLine (also byChunk) for reading lines or arbitrary sized blobs.

Based on your specific case, you’ll probably want to use slurp or readf. Your other option is to read lines and split them into the fields you want, then use std.conv.to to parse the textual representation:

double d = to!double(somestring);

In summary, if every line has the same format, slurp is the nicest way to go. Otherwise, you’ll have to decide what will be most convenient for you.