String.Format() Method in C# with Examples

The String.Format() method is used to create a formatted string by replacing placeholders with values from variables, objects, or expressions. It belongs to the System.String class and supports formatting numbers, dates, currencies, and other data types.

• Uses indexed placeholders such as {0}, {1}, and {2} to insert values.
• Supports custom formatting for numbers, dates, and text alignment.
• Allows culture-specific formatting using an IFormatProvider.

Syntax of String.Format()

string.Format(string format, params object[] args);

Parameters:

• format: A composite format string containing placeholders.
• args: The values used to replace the placeholders.

Return Value: Returns a new formatted string without modifying the original string.

using System;

class Geeks{
    public static void Main(String[] args){
        
        String s = "Geeks";

        // Using the String.Format Method
        String res = String.Format("Hello, {0}!", s);

        // Displaying the String
        Console.WriteLine(res);
    }
}

Hello, Geeks!

Explanation: The placeholder {0} is replaced by the value of name. Placeholder indexing starts at 0, so {1} refers to the second argument, and so on.

How String.Format() Works

The String.Format() method uses composite formatting to insert values into a predefined string.

Placeholder Syntax:

{index[,alignment][:formatString]}

For example, {0:F2} formats the first argument as a fixed-point number with two decimal places, while {1,-10} left-aligns the second argument within a field of at least 10 characters.

String.Format() Method Overloads

The String.Format() method provides several overloads to format one or more values, including overloads that accept an IFormatProvider.

Modern .NET versions also provide generic formatting overloads. The table above covers the commonly used object-based overloads.

Examples of String.Format()

Example 1: Formatting Multiple Values

The following example inserts multiple values into a formatted string.

using System;

class Geeks{
    static void Main(){
        
        string name = "Rahul";
        int age = 25;

        string result = string.Format("Name: {0}, Age: {1}",
                                      name, age);

        Console.WriteLine(result);
    }
}

Name: Rahul, Age: 25

Explanation: {0} is replaced with name, and {1} is replaced with age.

Example 2: Formatting Numbers

The following example uses the F2 format specifier to display a decimal value with two digits after the decimal point.

using System;
using System.Globalization;

class Geeks{
    static void Main(){
        double price = 123.456;

        string result
            = string.Format(CultureInfo.InvariantCulture,
                            "Price: {0:F2}", price);

        Console.WriteLine(result);
    }
}

Price: 123.46

Explanation: {0:F2} rounds the displayed value to two decimal places. InvariantCulture ensures that the decimal separator is a period.

Example 3: Formatting Dates

The following example formats a DateTime value using the specified culture.

using System;
using System.Globalization;

class Geeks{
    static void Main(){
        
        DateTime date = new DateTime(2025, 3, 16);

        CultureInfo culture = new CultureInfo("en-US");

        string result
            = string.Format(culture, "Date: {0:D}", date);

        Console.WriteLine(result);
    }
}

Date: Sunday, March 16, 2025

Explanation: The D format specifier displays the long date format, while en-US determines the date's culture-specific representation.

Example 4: Aligning Text

The following example uses alignment values to format text.

using System;

class Geeks{
    static void Main(){
        
        Console.WriteLine(
            string.Format("|{0,-10}|{1,10}|", "Name", "Marks"));

        Console.WriteLine(
            string.Format("|{0,-10}|{1,10}|", "Rahul", 95));
    }
}

|Name      |     Marks|
|Rahul     |        95|

Explanation: {0,-10} left-aligns text within a 10-character field, while {1,10} right-aligns the value within a 10-character field.

Common Format Specifiers

The following format specifiers can be used with String.Format() when supported by the argument's data type.

The results depend on the value's type and, for some specifiers, the selected culture.

Advantages of String.Format()

• Readable Formatting: Combines text and values using indexed placeholders.
• Flexible Output: Supports numeric, date, currency, and alignment formatting.
• Reusable Templates: The same format string can be reused with different values.
• Culture Support: Allows culture-specific formatting through IFormatProvider.

Limitations of String.Format()

• Runtime Errors: Invalid placeholders or missing arguments can cause a FormatException.
• Index Management: Managing numbered placeholders can become difficult in lengthy strings.
• Additional Allocation: Produces a new string rather than modifying an existing one.
• Readability: String interpolation is often easier to read for simple formatting expressions.