String.Format Method

Each overload of the Format method uses the composite formatting feature to include zero-based indexed placeholders, called format items, in a composite format string. At run time, each format item is replaced with the string representation of the corresponding argument in a parameter list. For example, the following call to the Format method includes a format string with three format items, {0}, {1}, and {2}, and an argument list with three items.

DateTime dat = new DateTime(2012, 1, 17, 9, 30, 0); 
string city = "Chicago";
int temp = -16;
string output = String.Format("At {0} in {1}, the temperature was {2} degrees.",
                              dat, city, temp);
Console.WriteLine(output);
// The example displays the following output: 
//    At 1/17/2012 9:30:00 AM in Chicago, the temperature was -16 degrees.   

A format item has the following syntax:

Brackets denote optional elements. The opening and closing brackets are required. A format item has the following elements:

index

The zero-based index of the argument whose string representation is to be included at this position in the string.

alignment

A signed integer that indicates the total length of the field into which the argument is inserted and whether it is right-aligned (a positive integer) or left-aligned (a negative integer). If alignment is omitted, the string representation of the corresponding argument is inserted in a field with no leading or trailing spaces.

formatString

A format string that specifies the format of the corresponding argument's result string. If formatString is omitted, the corresponding argument's parameterless ToString method is called to produce its string representation. If formatString is present, the argument referenced by the format item must implement the IFormattable interface. Types that support format strings include the following:

• All integral and floating-point types. (See Standard Numeric Format Strings and Custom Numeric Format Strings.)

• DateTime and DateTimeOffset. (See Standard Date and Time Format Strings and Custom Date and Time Format Strings.)

• All enumeration types. (See Enumeration Format Strings.)

• TimeSpan values. (See Standard TimeSpan Format Strings and Custom TimeSpan Format Strings.)

• GUIDs. (See the Guid.ToString(String) method.)

Reference

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