C# compiler number literals

问题:

Does anyone know the full list of C# compiler number literal modifiers?

By default declaring '0' makes it an Int32 and '0.0' makes it a 'Double'. I can use the literal modifier 'f' at the end to ensure something is treated as a 'Single' instead. For example like this...

var x = 0;    // x is Int32
var y = 0f;   // y is Single

What are the other modifiers I can use? Is there one for forcing to Double, Decimal, UInt32? I tried googling for this but could not find anything. Maybe my terminology is wrong and so that explains why I am coming up blank. Any help much appreciated.

回答1:

var y = 0f; // y is single
var z = 0d; // z is double
var r = 0m; // r is decimal
var i = 0U; // i is unsigned int
var j = 0L; // j is long (note capital L for clarity)
var k = 0UL; // k is unsigned long (note capital L for clarity)

From the C# specification 2.4.4.2 Integer literals and 2.4.4.3 Real literals. Take note that L and UL are preferred as opposed to their lowercase variants for clarity as recommended by Jon Skeet.

回答2:

If you don't want to have to remember them, then the compiler also accepts a cast for the same purpose (you can check the IL that the effect is the same - i.e. the compiler, not the runtime, does the cast). To borrow the earlier example:

    var y = (float)0; // y is single
    var z = (double)0; // z is double
    var r = (decimal)0; // r is decimal
    var i = (uint)0; // i is unsigned int
    var j = (long)0; // j is long
    var k = (ulong)0; // k is unsigned long

And for the record, I agree that "var" is a bad choice here; I'll happily use var for a SortedDictionary<SomeLongType, SomeOtherLongType>, but for "int" it is just lazy...

回答3:

You might want to start by looking at the C# language spec. Most of the types are listed in there, and have a suffix:

• L = long
• F = float
• U = uint
• ulong's are a little different
• m = decimal (money)
• D = double

Of course, if you stop using var then you get around the whole problem, and your code becomes more readable (ok, thats subjective, but for something like this, it's more readable by other people:

var x = 0; //whats x?
float x = 0; //oh, it's a float
byte x = 0; // or not!