What is the most accepted/used method to output a CSV string from an array?

Question

Trying to stay completely language agnostic, and avoiding built in methods like Split() and Join(), what are the most utilized or accepted methods to build a CSV string? I run into situations like this a lot, and I'm curious as to how methods like Split() implement this? I usually do something like this:

for(int i = 0; i < list.length; i++)
{
    if(i == list.length - 1)
    {
        Write(list[i]);
    }
    else
    {
        Write(list[i] + ',');
    }
}

But it seems like there should be a better way to do it.

Answer 1

Most implementations I've seen do something more like:

if (list.length > 0)
{
    Write(list[0]);
    for(int i = 1; i < list.length; i++)
    {
        Write(','); // Write separator character(s)
        Write(list[i]);
    }
}

This avoids the checking inside the for loop. The .NET Framework's Join() method uses this basic approach (with a lot more checking, of course).

Answer 2

You probably don't want to use Split, Join, or anything simplistic. What if your value contains a comma or a quote?

If possible, use a library. Otherwise, something like:

string escapeForCsv(string s) {
    if s.contains("\",\n") {
      needs_quotes = true
      s.replace("\"", "\"\"")
    }
    if needs_quotes {
      s = "\"" + s + "\""
    }
    return s
}

for (i := 0; i < array.length; i++) {
    elt = array[i]
    if i > 0 {
       Write(',')
    }
    Write(escapeForCsv(elt))
}