String formatting with braces

Question

I want to output a formatted number inside braces (example {$100.00}) using a string.Format(fmt, x) statement with x=100.

{ 
    var x = 100M;
    // works fine without a format specifier
    string.Format("{{{0}}}", x);    // "{100.00}"

    // fails with a format specifier
    string.Format("{{{0:C}}}", x);  // "{C}"

    // works with spaces
    string.Format("{{ {0:C} }}", x);  // "{ $100.00 }"
}

So what format string should I use above to get {$100} without using a clunky solution such as string.Format("{0}{1:C}{2}", "{", x, "}");

Answer 1

This is actually documented on MSDN under Composite Formatting:

The way escaped braces are interpreted can lead to unexpected results. For example, consider the format item "{{{0:D}}}", which is intended to display an opening brace, a numeric value formatted as a decimal number, and a closing brace. However, the format item is actually interpreted in the following manner:

1. The first two opening braces ("{{") are escaped and yield one opening brace.
2. The next three characters ("{0:") are interpreted as the start of a format item.
3. The next character ("D") would be interpreted as the Decimal standard numeric format specifier, but the next two escaped braces ("}}") yield a single brace. Because the resulting string ("D}") is not a standard numeric format specifier, the resulting string is interpreted as a custom format string that means display the literal string "D}".
4. The last brace ("}") is interpreted as the end of the format item.
5. The final result that is displayed is the literal string, "{D}". The numeric value that was to be formatted is not displayed.

One way to write your code to avoid misinterpreting escaped braces and format items is to format the braces and format item separately. That is, in the first format operation display a literal opening brace, in the next operation display the result of the format item, then in the final operation display a literal closing brace. The following example illustrates this approach.

int value = 6324;
string output = string.Format("{0}{1:D}{2}", 
                             "{", value, "}");
Console.WriteLine(output);
// The example displays the following output: 
//       {6324}

(note that I add the code only because it's referenced in the MSDN article - not to suggest it as a solution.)

If you're not concerned about culture differences you could use "{{{0:$#,##0.00}}}" as a format string.

Answer 2

Try to use this code:

string.Format("{{{0}}}", x.ToString("C"))

Answer 3

Depending on the application you may be able to use a zero-width space to trick the string.Format method into doing what you want. See Spaces in Unicode for a list of options, but \x200B will add a zero-width space to a C# string, so you could try using:

string.Format("Pi is {{{0:N2}\x200B}} when rounded", Math.PI)

which should result in Pi is {3.14​} when rounded when displayed in an application that supports unicode. If the application doesn't support unicode it may end up looking like Pi is {3.14​} when rounded