String.Format Method (String, Object)
Replaces one or more format items in a specified string with the string representation of a specified object.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- format
- Type: System.String
A composite format string (see Remarks).
- arg0
- Type: System.Object
The object to format.
Return Value
Type: System.StringA copy of format in which any format items are replaced by the string representation of arg0.
| Exception | Condition |
|---|---|
| ArgumentNullException | format is a null reference (Nothing in Visual Basic). |
| FormatException | The format item in format is invalid. -or- The index of a format item is not zero. |
This method uses the composite formatting feature of the .NET Framework to convert the value of an object to its string representation and to embed that representation in a string. The .NET Framework provides extensive formatting support, which is described in greater detail in the following formatting topics:
For more information about the composite formatting feature supported by methods such as Format, AppendFormat, and some overloads of WriteLine, see Composite Formatting.
For more information about numeric format specifiers, see Standard Numeric Format Strings and Custom Numeric Format Strings.
For more information about date and time format specifiers, see Standard Date and Time Format Strings and Custom Date and Time Format Strings.
For more information about enumeration format specifiers, see Enumeration Format Strings.
For more information about formatting, see Formatting Types.
The format parameter consists of zero or more runs of text intermixed with zero or more indexed placeholders, called format items, that correspond to an object in the parameter list of this method. The formatting process replaces each format item with the string representation of the value of the corresponding object.
The syntax of a format item is as follows:
{index[,length][:formatString]}
Elements in square brackets are optional. The following table describes each element. For more information about the composite formatting feature, including the syntax of a format item, see Composite Formatting.
Element | Description |
|---|---|
index | The zero-based position in the parameter list of the object to be formatted. If the object specified by index is a null reference (Nothing in Visual Basic), the format item is replaced by String.Empty. Because this overload has only a single object in its parameter list, the value of index must always be 0. If there is no parameter in the index position, a FormatException is thrown. |
,length | The minimum number of characters in the string representation of the parameter. If positive, the parameter is right-aligned; if negative, it is left-aligned. |
:formatString | A standard or custom format string that is supported by the object to be formatted. Possible values for formatString are the same as the values supported by the object's ToString(format) method. If formatString is not specified and the object to be formatted implements the IFormattable interface, a null reference (Nothing in Visual Basic) is passed as the value of the format parameter that is used as the IFormattable.ToString format string. |
Note |
|---|
For the standard and custom format strings used with date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings. For the standard and custom format strings used with numeric values, see Standard Numeric Format Strings and Custom Numeric Format Strings. For the standard format strings used with enumerations, see Enumeration Format Strings. |
The leading and trailing brace characters, "{" and "}", are required. To specify a single literal brace character in format, specify two leading or trailing brace characters; that is, "{{" or "}}".
Although the String.Format(String, Object) method has a single object in the parameter list, format can include more than one format item as long as each has the same index. In the following example, the format string includes two format items: one displays the decimal value of a number and the other displays its hexadecimal value.
If the string assigned to format is "Thank you for your donation of {0:####} cans of food to our charitable organization." and arg0 is an integer with the value 10, the return value will be "Thank you for your donation of 10 cans of food to our charitable organization."
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Note