Can I use StringBuilder elements in a foreach?

Question

Since I'm using .NET 1.1, I can't use a generic List of string, as generics were not part of the language yet. So I'm trying to use a StringBuilder, but get this err msg:

"foreach statement cannot operate on variables of type 'System.Text.StringBuilder' because 'System.Text.StringBuilder' does not contain a definition for 'GetEnumerator', or it is inaccessible"

with this code:

public StringBuilder linesToSend;
. . .

foreach (string _line in this.linesToSend)
{
    serialPort.Write(_line);
}

Is there something wrong with my code, or is StringBuilder really disallowed from foreach loops? If the latter, is String[] my best recourse?

Solution 1

A StringBuilder doesn't store the lines that you append. It simply is used to build the final string. Assuming you've added everything to the StringBuilder already, you can do:

// Write the complete string to the serialPort
serialPort.Write(linesToSend.ToString());

Solution 2

Old question, I know, but something potentially useful:

If each of your strings were built with .AppendLine or you inserted a new line, you can do

string[] delim = { Environment.NewLine, "\n" }; // "\n" added in case you manually appended a newline
string[] lines = StringBuilder.ToString().Split(delim, StringSplitOptions.None);
foreach(string line in lines){
    // Do something
}

Solution 3

This is correct. A StringBuilder is designed to help you build one final output string as the others have stated.

If you have a variable number of strings you need to work on, you can use an ArrayList and iterate over that.

ArrayList strings = new ArrayList();
// populate the list
foreach (string str in strings) {
  // do what you need to.
}

If you're afraid that the array list might contain other objects (as it isn't strongly typed) you can cast it safely instead:

foreach (object obj in strings) {
  string str = obj as string;
  // If null strings aren't allowed, you can use the following
  // to skip to the next element.
  if (str == null) {
    continue;
  }
}

Solution 4

A StringBuilder is building just one string, so how could you foreach it to get a whole sequence of strings?

If you need to write line by line, maybe use an ArrayList, add each line string to that, and foreach with string as the foreach variable type (Object will be cast to String). Or even better, use StringCollection (thank to comment by Anthony Pegram, to the original question; I had forgotten this class).

But why not upgrade to a newer version of .NET?

Solution 5

The foreach loop works by calling the GetEnumerator from the interface IEnumerable which will return an enumerator that foreach uses to get the next element of the object.

StringBuilder does not implement IEnumerable or IEnumerable<T> which would allow the foreach to work. You are better off using a string[] or StringCollection in this case and when you are done you can concatenate the collection using a StringBuilder.

ex:

StringBuilder stringBuilder = new StringBuilder();
foreach(string line in array)
{
    serialPort.Write(line);
    stringBuilder.Append(line);
}

View more solutions

Comments

[B. Clay Shannon-B. Crow Raven]

For this project, I can't upgrade. In other project, I AM using Visual Studio 2010 on Windows 7 and VS 2012 on Windows 8, but this project will remain in VS 2003 / .NET 1.1

[Captain Kenpachi]

It is mutable, i.e. you don't have to indicate the number of items you're going to put into it beforehand. Although, I meant Collection rather than Dictionary. sorry.

[supercat]

The foreach loop actually duck-types its operand. If the operand has a method called GetEnumerator whose return type includes a parameterless method called MoveNext that returns bool, and a readable property named Current that returns the control-variable type, then foreach will use without regard for whether the type implements IEnumerable or IEnumerable<T> [if the type explicitly implements IEnumerable<T>, but defines a GetEnumerator method separate from the interface, a foreach loop will use the latter].