How to: Add a string to a string array using File.ReadAllLines

Question

How to: Add a string to a string array using File.ReadAllLines

I think the question is clear: I want to add a new string to an existing string array, which gets ist content from a File.ReadAllLines.

public void CreateNewFolder()
{
    string[] lines = File.ReadAllLines(stringFile, Encoding.UTF8);
    lines[lines.Length + 1] = "Test";
    File.WriteAllLines(stringFile, lines, Encoding.UTF8);
}

The index of the array is "too small", but I do not know why.

duplicate: http://stackoverflow.com/questions/1440265/how-to-add-a-string-to-a-string-array-theres-no-add-function — st4hoo, May 30 '14 at 09:59

score 3 · Accepted Answer · answered May 30 '14 at 10:01

3

The error is caused since the length of the array is fixed and the and the last index (where you wanna add the new item) is always outside the array. You can use a list instead:

public void CreateNewFolder()
{
    List<String> lines = File.ReadAllLines(stringFile, Encoding.UTF8).ToList();
    lines.Add("Test");
    File.WriteAllLines(stringFile, lines.ToArray(), Encoding.UTF8);
    //Calling the ToArray method for lines is not necessary 
}

answered May 30 '14 at 10:01

Transcendent

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You might want to add to your answer that he gets the error because an array has a fixed length once defined. List is the way to go. +1 – middelpat May 30 '14 at 10:02
There is no definition for `ToList()`. – sjantke May 30 '14 at 10:03
@middelpat: Good suggestion, will add it – Transcendent May 30 '14 at 10:03
2

@Exception include "using System.Linq;" – middelpat May 30 '14 at 10:03
Final answer! Perfect. Thank you very much! – sjantke May 30 '14 at 10:06
Additional question: What's the difference between `List` and `List`? – sjantke May 30 '14 at 10:07
String is a System type while string is a built in type – Transcendent May 30 '14 at 10:07
Actually, no difference. – amnezjak May 30 '14 at 10:30
@amnezjak: The difference is only visible when use the System String in C++, then the way it works will be really really different from string and casting these two is also a long story (C++), but in C# they are the same. – Transcendent May 30 '14 at 11:07

dkozl · Answer 2 · 2014-05-30T10:20:20.110

0

You get the error because you try to change an item beyond current array length. You can use Array.Resize<T> to resize array first and then change last item

public void CreateNewFolder()
{
    string[] lines = File.ReadAllLines(stringFile, Encoding.UTF8);
    Array.Resize(ref lines, lines.Length + 1);
    lines[lines.Length - 1] = "Test";
    File.WriteAllLines(stringFile, lines, Encoding.UTF8);
}

edited May 30 '14 at 10:20

answered May 30 '14 at 10:04

dkozl

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How to: Add a string to a string array using File.ReadAllLines

2 Answers2