如何在C＃中根据参数在命令行或文件中输出字符串？

Question

How to output string on command line or in a file, depending on a parameter, in C#?

I have parameter:

bool console = true; // or false

then I have some code that creates a StringBuilder. I want to output to either Console or to a StreamWriter, based on the console variable.

The tricky part is:

1. I need to write in small pieces, not a whole string at a time

2. Given 1) I will end up with code like:

    if (console ) { Console.WriteLine(someString); } else { using (StreamWriter writer = new StreamWriter(file)) { writer.WriteLine(someString); } } 

every single time I need to add to the string!

So how do I escape this code bloat?

Answer 1

You do not need to create an interface yourself; you can simply change your code to take a TextWriter as an input:

private void DoSomethingAndWriteLog(TextWriter writer)
{
    // Do something
    var someString = "Test";
    writer.WriteLine(someString);
}

Then you can call this method both using Console. Out and a custom TextWriter:

if (console)
{
    DoSomethingAndWriteLog(Console.Out);
} 
else 
{
    using (StreamWriter writer = new StreamWriter(file)) 
    {
        DoSomethingAndWriteToLog(writer);
    }
}

Answer 2

As a generalized case, you define an output writer interface,

interface IOutputWriter
{
    void WriteLine(string s);
}

then write 2 classes that conform to that interface, and inject the appropriate one into your code.

void YourCode (IOutputWriter writer)
{ 
     // ...
     writer.WriteLine(output);
}

void Main()
{
    IOutputWriter writer;
    if (console)
    { 
        writer = new ConsoleWriter();
    }
    else
    { 
        writer = new StreamWriter();
    }
    YourCode (writer);

}

You can then later define new implementations of IOutputWriter to cope with new requirements (eg: PrinterWriter, DatabaseWriter, etc).

Answer 3

You can make Console.WriteLine output to file, by invoking Console.SetOut and passing a StreamWriter as a parameter:

if (needToOutputToFile)
{
    Console.SetOut (streamWriter);
}
Console.WriteLine ("This is written in a file, if needToOutputToFile is true");

Answer 4

You can try using Console.Out standard writer and trenary operator :

  using (TextWriter writer = console ? Console.Out : new StreamWriter(file)) {
    ...
    writer.WriteLine(someString);
    ...
  }