c# string formatting

Question

I m curious why would i use string formatting while i can use concatenation such as

Console.WriteLine(\"Hello {0} !\", name);

Console.WriteLine(\"Hello \"+          


        

Answer 1

It depends: http://geekswithblogs.net/BlackRabbitCoder/archive/2010/05/10/c-string-compares-and-concatenations.aspx

Answer 2

I have found the former approach (using string.format) very useful when overriding ToString() methods in Entity classes.

For example, in my Product class;

public override string ToString()
{
    return string.format("{0} : {1} ({2} / {3} / {4}",
                              this.id,
                              this.description,
                              this.brand,
                              this.model);
}

Then, when users decide they want the product to appear differently it's easy to change the order/contents or layout of the string that is returned.

Of course you still concatentate this string together but I feel string.Format makes the whole thing a bit more readable and maintainable.

I guess that's the short answer I'm giving then isn't it - readability and maintainability for lengthy or complex strings.

Answer 3

There isn't a singular correct answer to this question. There are a few issues you want to address:

Performance

The performance differences in your examples (and in real apps) are minimal. If you start writing MANY concatenations, you will gradually see better memory performance with the formatted string. Refer to Ben's answer

Readability

You will be better off with a formatted string when you have formatting, or have many different variables to stringify:

string formatString = "Hello {0}, today is {1:yyyy-MM-dd}";
Console.WriteLine(formatString, userName, Date.Today);

Extensibility

Your situation will determine what's best. You tell me which is better when you need to add an item between Username and Time in the log:

Console.WriteLine(
   @"Error! 
    Username: " + userName + "
    Time: " + time.ToString("HH:mm:ss") + "
    Function: " + functionName + "
    Action: " + actionName + "
    status: " + status + "
   ---");

or

Console.WriteLine(@"Error! 
    Username: {0}
    Time: {1}
    Function: {2}
    Action: {3}
    status: {4}
   ---",
    username, time.ToString("HH:mm:ss"), functionName, actionName, status);

Conclusion

I would choose the formatted string most of the time... But I wouldn't hesitate at all to use concatenation when it was easier.

Answer 4

Since C# 6 release a few years ago, it is also possible to perform string interpolation. Per example this:

var n = 12.5847;
System.Console.WriteLine(string.Format("Hello World! {0:C2}", n));

Becomes that:

var n = 12.5847;
System.Console.WriteLine($"Hello World! {n:C2}");

And both give you this result:

Hello World! £12.58

Answer 5

I think the main thing here is readability. So I always choose for what have the best readability for each case.

Note:

With string interpolation of C# 6 your code could be simplified to this:

Console.WriteLine($"Hello {name}!");

Which I think better than your two suggested options.

Answer 6

You can trade the string for a dynamic string later.

For example:

// In a land far, far away
string nameFormat = "{0} {1}";

// In our function
string firstName = "John";
string lastName = "Doe";

Console.WriteLine(nameFormat, firstName, lastName);

Here, you can change nameFormat to e.g. "{1}, {0}" and you don't need to change any of your other code. With concatination, you would need to edit your code or possibly duplicate your code to handle both cases.

This is useful in localization/internationalization.