String.Format does not provide correct result for number format

Question

Why does the following output provide incorrect result,

int myNumber = 95;            
Console.WriteLine(String.Format("{{{0:N}}}", myNumber ));

Output is {N} rather then {95.00} as expected.

Am I misunderstanding the concept of escaping { } or doing something wrong with Number format?

Answer 1

Your understanding is correct: Use two braces to create a single literal brace. The problem, however, is that in the string }}}, the first two braces are interpreted as a literal brace, rather than the second and the third, as you intended.

In fact, your example is explicitly listed on the corresponding MSDN page as a possible problem (highlighting by me):

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:

...

• The next character ("D") would be interpreted as the Decimal standard numeric format specifier, but the next two escaped braces ("}}") yield a single brace.

The suggested solution is to use something like this:

int myNumber = 95;            
Console.WriteLine(String.Format("{0}{1:N}{2}", "{", myNumber, "}"));

Answer 2

Yes, the ouptut given is perfectly right and your understanding is also right that {, } in string.Format should be escaped by {, } respectively and to format string in Number you have to use {0:N}.

But when you are looking for output {95.00} the format {{{0:N}}} do not work as expected, for this we should undesrstand how the above statement is interpreted,

• The first two curly brackets are escaped as we understand { followed by {,

  prints { at output

• Then we have a formatting section {0:N}}} but compiler is confused that } is ending brace of {0:N or it is escaped brace as it is followed by } which result in formation of custom format 0:N}. but rules say it should be considered as custom format, thus it is actually interpreted as containing 0:N}
• Since neither N or } mean anything for a custom numeric format, these characters are simply written out, rather than the value of the variable referenced.

Thus we have output, {N}.

The detail explanation for above can be found at string Format FAQ

If you are looking for output {95.00} then either use {{ {0:N} }} and it will provide 95.00 as output with space.

EDIT The solution by Heinzi is perfectly right for the output you are expecting,

Console.WriteLine(String.Format("{0}{1:N}{2}", "{", myNumber, "}"));