Compiler error “Default parameter specifiers are not permitted”

问题

Below is my code.

public class PItem
{
    public String content;
    public int count;
    public int fee;
    public int amount;
    public string description;

    // Default values
    public PItem(String _content = "", int _count = 0, int _fee = 0, string _description = "", int _amount = 0)
    {
        content = _content;
        count = _count < 0 ? 0 : _count;
        fee = _fee;
        description = _description;
        amount = _amount < 0 ? 0 : _amount;
    }
}

This is inside in a class. When I try to run a program it gives this error:

Default parameter specifiers are not permitted

How can I solve this error?

回答1:

The problem is that you cannot have optional parameters in C# version less than 4.
You can find more information on this here.

You can solve it like this:

public class PItem
{
  public String content;
  public int count;
  public int fee;
  public int amount;
  public String description;
  // default values
  public PItem(): this("", 0, 0, "", 0) {}
  public PItem(String _content): this (_content, 0, 0, "", 0) {}
  public PItem(String _content, int _count): this(_content, _count, 0, "", 0) {}
  public PItem(String _content, int _count, int _fee): this(_content, _count, _fee, "", 0) {}
  public PItem(String _content, int _count, int _fee, string _description): this(_content, _count, _fee, _description, 0) {}
  public PItem(String _content, int _count, int _fee, string _description, int _amount)
  {
      content = _content;
      count = _count < 0 ? 0 : _count;
      fee = _fee;
      description = _description;
      amount = _amount < 0 ? 0 : _amount;
  }
}

回答2:

If your project seems to be set as .NET 4.0 then change it to for example 3.5 and then change to the 4.0 again. I got this error when I included a class library project from my old solution solution to a new one when I wanted to have the project in my new software. Both solutions were .NET 4 but I got "default parameter specifiers are not permitted" error. I just did what I explained.

来源：https://stackoverflow.com/questions/6398382/compiler-error-default-parameter-specifiers-are-not-permitted