String.Join Method

Definition

Concatenates the elements of a specified array or the members of a collection, using the specified separator between each element or member.

Overloads

Join(Char, Object[])

Concatenates the string representations of an array of objects, using the specified separator between each member.

Join(Char, ReadOnlySpan<Object>)

Concatenates the string representations of a span of objects, using the specified separator between each member.

Join(Char, ReadOnlySpan<String>)

Concatenates a span of strings, using the specified separator between each member.

Join(Char, String[])

Concatenates an array of strings, using the specified separator between each member.

Join(String, IEnumerable<String>)

Concatenates the members of a constructed IEnumerable<T> collection of type String, using the specified separator between each member.

Join(String, Object[])

Concatenates the elements of an object array, using the specified separator between each element.

Join(String, ReadOnlySpan<Object>)

Concatenates the string representations of a span of objects, using the specified separator between each member.

Join(String, ReadOnlySpan<String>)

Concatenates a span of strings, using the specified separator between each member.

Join(String, String[])

Concatenates all the elements of a string array, using the specified separator between each element.

Join(Char, String[], Int32, Int32)

Concatenates an array of strings, using the specified separator between each member, starting with the element in value located at the startIndex position, and concatenating up to count elements.

Join(String, String[], Int32, Int32)

Concatenates the specified elements of a string array, using the specified separator between each element.

Join<T>(String, IEnumerable<T>)

Concatenates the members of a collection, using the specified separator between each member.

Join<T>(Char, IEnumerable<T>)

Concatenates the members of a collection, using the specified separator between each member.

Join(Char, Object[])

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates the string representations of an array of objects, using the specified separator between each member.

public static string Join (char separator, params object?[] values);
public static string Join (char separator, params object[] values);

Parameters

separator
Char

The character to use as a separator. separator is included in the returned string only if values has more than one element.

values
Object[]

An array of objects whose string representations will be concatenated.

Returns

A string that consists of the elements of values delimited by the separator character.

-or-

Empty if values has zero elements.

Exceptions

values is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Applies to

.NET 9 and other versions
Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Standard 2.1

Join(Char, ReadOnlySpan<Object>)

Concatenates the string representations of a span of objects, using the specified separator between each member.

public static string Join (char separator, scoped ReadOnlySpan<object?> values);

Parameters

separator
Char

The character to use as a separator. separator is included in the returned string only if value has more than one element.

values
ReadOnlySpan<Object>

A span of objects whose string representations will be concatenated.

Returns

A string that consists of the elements of values delimited by the separator character. -or- Empty if values has zero elements.

Applies to

.NET 9
Product Versions
.NET 9

Join(Char, ReadOnlySpan<String>)

Concatenates a span of strings, using the specified separator between each member.

public static string Join (char separator, scoped ReadOnlySpan<string?> value);

Parameters

separator
Char

The character to use as a separator. separator is included in the returned string only if value has more than one element.

value
ReadOnlySpan<String>

A span that contains the elements to concatenate.

Returns

A string that consists of the elements of value delimited by the separator string. -or- Empty if value has zero elements.

Applies to

.NET 9
Product Versions
.NET 9

Join(Char, String[])

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates an array of strings, using the specified separator between each member.

public static string Join (char separator, params string?[] value);
public static string Join (char separator, params string[] value);

Parameters

separator
Char

The character to use as a separator. separator is included in the returned string only if value has more than one element.

value
String[]

An array of strings to concatenate.

Returns

A string that consists of the elements of value delimited by the separator character.

-or-

Empty if value has zero elements.

Exceptions

value is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Applies to

.NET 9 and other versions
Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Standard 2.1

Join(String, IEnumerable<String>)

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates the members of a constructed IEnumerable<T> collection of type String, using the specified separator between each member.

public static string Join (string separator, System.Collections.Generic.IEnumerable<string> values);
public static string Join (string? separator, System.Collections.Generic.IEnumerable<string?> values);
[System.Runtime.InteropServices.ComVisible(false)]
public static string Join (string separator, System.Collections.Generic.IEnumerable<string> values);

Parameters

separator
String

The string to use as a separator.separator is included in the returned string only if values has more than one element.

values
IEnumerable<String>

A collection that contains the strings to concatenate.

Returns

A string that consists of the elements of values delimited by the separator string.

-or-

Empty if values has zero elements.

Attributes

Exceptions

values is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Examples

The following example uses the Sieve of Eratosthenes algorithm to calculate the prime numbers that are less than or equal to 100. It assigns the result to a List<T> object of type String, which it then passes to the Join(String, IEnumerable<String>) method.

using System;
using System.Collections.Generic;

public class Example
{
   public static void Main()
   {
      int maxPrime = 100;
      List<int> primes = GetPrimes(maxPrime);
      Console.WriteLine("Primes less than {0}:", maxPrime);
      Console.WriteLine("   {0}", String.Join(" ", primes));
   }

   private static List<int> GetPrimes(int maxPrime)
   {
      Array values = Array.CreateInstance(typeof(int), 
                              new int[] { maxPrime - 1}, new int[] { 2 });
      // Use Sieve of Eratosthenes to determine prime numbers.
      for (int ctr = values.GetLowerBound(0); ctr <= (int) Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))); ctr++)
      {
                           
         if ((int) values.GetValue(ctr) == 1) continue;
         
         for (int multiplier = ctr; multiplier <=  maxPrime / 2; multiplier++)
            if (ctr * multiplier <= maxPrime)
               values.SetValue(1, ctr * multiplier);
      }      
      
      List<int> primes = new List<int>();
      for (int ctr = values.GetLowerBound(0); ctr <= values.GetUpperBound(0); ctr++)
         if ((int) values.GetValue(ctr) == 0) 
            primes.Add(ctr);
      return primes;
   }   
}
// The example displays the following output:
//    Primes less than 100:
//       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Remarks

If separator is null, an empty string (String.Empty) is used instead. If any member of values is null, an empty string is used instead.

Join(String, IEnumerable<String>) is a convenience method that lets you concatenate each element in an IEnumerable(Of String) collection without first converting the elements to a string array. It is particularly useful with Language-Integrated Query (LINQ) query expressions. The following example passes a List(Of String) object that contains either the uppercase or lowercase letters of the alphabet to a lambda expression that selects letters that are equal to or greater than a particular letter (which, in the example, is "M"). The IEnumerable(Of String) collection returned by the Enumerable.Where method is passed to the Join(String, IEnumerable<String>) method to display the result as a single string.

using System;
using System.Collections.Generic;
using System.Linq;

public class Example
{
   public static void Main()
   {
      string output = String.Join(" ", GetAlphabet(true).Where( letter => 
                      letter.CompareTo("M") >= 0));
      Console.WriteLine(output);  
   }

   private static List<string> GetAlphabet(bool upper)
   {
      List<string> alphabet = new List<string>();
      int charValue = upper ? 65 : 97;
      for (int ctr = 0; ctr <= 25; ctr++)
         alphabet.Add(((char)(charValue + ctr)).ToString());
      return alphabet; 
   }
}
// The example displays the following output:
//      M N O P Q R S T U V W X Y Z

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

Join(String, Object[])

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates the elements of an object array, using the specified separator between each element.

public static string Join (string separator, params object[] values);
public static string Join (string? separator, params object?[] values);
[System.Runtime.InteropServices.ComVisible(false)]
public static string Join (string separator, params object[] values);

Parameters

separator
String

The string to use as a separator. separator is included in the returned string only if values has more than one element.

values
Object[]

An array that contains the elements to concatenate.

Returns

A string that consists of the elements of values delimited by the separator string.

-or-

Empty if values has zero elements.

-or-

.NET Framework only: Empty if the first element of values is null.

Attributes

Exceptions

values is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Examples

The following example uses the Sieve of Eratosthenes algorithm to calculate the prime numbers that are less than or equal to 100. It assigns the result to a integer array, which it then passes to the Join(String, Object[]) method.

using System;
using System.Collections.Generic;

public class Example
{
   public static void Main()
   {
      int maxPrime = 100;
      int[] primes = GetPrimes(maxPrime);
      Console.WriteLine("Primes less than {0}:", maxPrime);
      Console.WriteLine("   {0}", String.Join(" ", primes));
   }

   private static int[] GetPrimes(int maxPrime)
   {
      Array values = Array.CreateInstance(typeof(int), 
                              new int[] { maxPrime - 1}, new int[] { 2 }); 
      // Use Sieve of Eratosthenes to determine prime numbers.
      for (int ctr = values.GetLowerBound(0); ctr <= (int) Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))); ctr++)
      {
                           
         if ((int) values.GetValue(ctr) == 1) continue;
         
         for (int multiplier = ctr; multiplier <=  maxPrime / 2; multiplier++)
            if (ctr * multiplier <= maxPrime)
               values.SetValue(1, ctr * multiplier);
      }      
      
      List<int> primes = new List<int>();
      for (int ctr = values.GetLowerBound(0); ctr <= values.GetUpperBound(0); ctr++)
         if ((int) values.GetValue(ctr) == 0) 
            primes.Add(ctr);
      return primes.ToArray();
   }   
}
// The example displays the following output:
//    Primes less than 100:
//       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Remarks

If separator is null or if any element of values other than the first element is null, an empty string (String.Empty) is used instead. See the Notes for Callers section if the first element of values is null.

Join(String, Object[]) is a convenience method that lets you concatenate each element in an object array without explicitly converting its elements to strings. The string representation of each object in the array is derived by calling that object's ToString method.

Notes to Callers

.NET Framework only: If the first element of values is null, the Join(String, Object[]) method does not concatenate the elements in values but instead returns Empty. A number of workarounds for this issue are available. The easiest is to assign a value of Empty to the first element of the array, as the following example shows.

object[] values = { null, "Cobb", 4189, 11434, .366 };
if (values[0] == null) values[0] = String.Empty;
Console.WriteLine(String.Join("|", values));

// The example displays the following output:
//      |Cobb|4189|11434|0.366

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

Join(String, ReadOnlySpan<Object>)

Concatenates the string representations of a span of objects, using the specified separator between each member.

public static string Join (string? separator, scoped ReadOnlySpan<object?> values);

Parameters

separator
String

The string to use as a separator. separator is included in the returned string only if values has more than one element.

values
ReadOnlySpan<Object>

A span of objects whose string representations will be concatenated.

Returns

A string that consists of the elements of values delimited by the separator string. -or- Empty if values has zero elements.

Applies to

.NET 9
Product Versions
.NET 9

Join(String, ReadOnlySpan<String>)

Concatenates a span of strings, using the specified separator between each member.

public static string Join (string? separator, scoped ReadOnlySpan<string?> value);

Parameters

separator
String

The string to use as a separator. separator is included in the returned string only if value has more than one element.

value
ReadOnlySpan<String>

A span that contains the elements to concatenate.

Returns

A string that consists of the elements of value delimited by the separator string. -or- Empty if value has zero elements.

Applies to

.NET 9
Product Versions
.NET 9

Join(String, String[])

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates all the elements of a string array, using the specified separator between each element.

public static string Join (string separator, params string[] value);
public static string Join (string? separator, params string?[] value);
public static string Join (string separator, string[] value);

Parameters

separator
String

The string to use as a separator. separator is included in the returned string only if value has more than one element.

value
String[]

An array that contains the elements to concatenate.

Returns

A string that consists of the elements in value delimited by the separator string.

-or-

Empty if value has zero elements.

Exceptions

value is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Examples

The following example demonstrates the Join method.

using System;

public class JoinTest
{
    public static void Main()
    {
        Console.WriteLine(MakeLine(0, 5, ", "));
        Console.WriteLine(MakeLine(1, 6, "  "));
        Console.WriteLine(MakeLine(9, 9, ": "));
        Console.WriteLine(MakeLine(4, 7, "< "));
    }

    private static string MakeLine(int initVal, int multVal, string sep)
    {
        string [] sArr = new string [10];

        for (int i = initVal; i < initVal + 10; i++)
            sArr[i - initVal] = String.Format("{0,-3}", i * multVal);

        return String.Join(sep, sArr);
    }
}
// The example displays the following output:
//       0  , 5  , 10 , 15 , 20 , 25 , 30 , 35 , 40 , 45
//       6    12   18   24   30   36   42   48   54   60
//       81 : 90 : 99 : 108: 117: 126: 135: 144: 153: 162
//       28 < 35 < 42 < 49 < 56 < 63 < 70 < 77 < 84 < 91

Remarks

For example, if separator is ", " and the elements of value are "apple", "orange", "grape", and "pear", Join(separator, value) returns "apple, orange, grape, pear".

If separator is null, an empty string (String.Empty) is used instead. If any element in value is null, an empty string is used instead.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

Join(Char, String[], Int32, Int32)

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates an array of strings, using the specified separator between each member, starting with the element in value located at the startIndex position, and concatenating up to count elements.

public static string Join (char separator, string?[] value, int startIndex, int count);
public static string Join (char separator, string[] value, int startIndex, int count);

Parameters

separator
Char

Concatenates an array of strings, using the specified separator between each member, starting with the element located at the specified index and including a specified number of elements.

value
String[]

An array of strings to concatenate.

startIndex
Int32

The first item in value to concatenate.

count
Int32

The number of elements from value to concatenate, starting with the element in the startIndex position.

Returns

A string that consists of count elements of value starting at startIndex delimited by the separator character.

-or-

Empty if count is zero.

Exceptions

value is null.

startIndex or count are negative.

-or-

startIndex is greater than the length of value - count.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Applies to

.NET 9 and other versions
Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Standard 2.1

Join(String, String[], Int32, Int32)

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates the specified elements of a string array, using the specified separator between each element.

public static string Join (string separator, string[] value, int startIndex, int count);
public static string Join (string? separator, string?[] value, int startIndex, int count);

Parameters

separator
String

The string to use as a separator. separator is included in the returned string only if value has more than one element.

value
String[]

An array that contains the elements to concatenate.

startIndex
Int32

The first element in value to use.

count
Int32

The number of elements of value to use.

Returns

A string that consists of count elements of value starting at startIndex delimited by the separator character.

-or-

Empty if count is zero.

Exceptions

value is null.

startIndex or count is less than 0.

-or-

startIndex plus count is greater than the number of elements in value.

Out of memory.

Examples

The following example concatenates two elements from an array of names of fruit.

String[] val = {"apple", "orange", "grape", "pear"};
String sep   = ", ";
String result;

Console.WriteLine("sep = '{0}'", sep);
Console.WriteLine("val[] = {{'{0}' '{1}' '{2}' '{3}'}}", val[0], val[1], val[2], val[3]);
result = String.Join(sep, val, 1, 2);
Console.WriteLine("String.Join(sep, val, 1, 2) = '{0}'", result);

// This example produces the following results:
// sep = ', '
// val[] = {'apple' 'orange' 'grape' 'pear'}
// String.Join(sep, val, 1, 2) = 'orange, grape'

Remarks

For example, if separator is ", " and the elements of value are "apple", "orange", "grape", and "pear", Join(separator, value, 1, 2) returns "orange, grape".

If separator is null, an empty string (String.Empty) is used instead. If any element in value is null, an empty string is used instead.

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

Join<T>(String, IEnumerable<T>)

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates the members of a collection, using the specified separator between each member.

public static string Join<T> (string separator, System.Collections.Generic.IEnumerable<T> values);
public static string Join<T> (string? separator, System.Collections.Generic.IEnumerable<T> values);
[System.Runtime.InteropServices.ComVisible(false)]
public static string Join<T> (string separator, System.Collections.Generic.IEnumerable<T> values);

Type Parameters

T

The type of the members of values.

Parameters

separator
String

The string to use as a separator. separator is included in the returned string only if values has more than one element.

values
IEnumerable<T>

A collection that contains the objects to concatenate.

Returns

A string that consists of the elements of values delimited by the separator string.

-or-

Empty if values has no elements.

Attributes

Exceptions

values is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Examples

The following example uses the Sieve of Eratosthenes algorithm to calculate the prime numbers that are less than or equal to 100. It assigns the result to a List<T> object of type integer, which it then passes to the Join<T>(String, IEnumerable<T>) method.

using System;
using System.Collections.Generic;

public class Example
{
   public static void Main()
   {
      int maxPrime = 100;
      List<int> primes = GetPrimes(maxPrime);
      Console.WriteLine("Primes less than {0}:", maxPrime);
      Console.WriteLine("   {0}", String.Join(" ", primes));
   }

   private static List<int> GetPrimes(int maxPrime)
   {
      Array values = Array.CreateInstance(typeof(int), 
                              new int[] { maxPrime - 1}, new int[] { 2 });
      // Use Sieve of Eratosthenes to determine prime numbers.
      for (int ctr = values.GetLowerBound(0); ctr <= (int) Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))); ctr++)
      {
                           
         if ((int) values.GetValue(ctr) == 1) continue;
         
         for (int multiplier = ctr; multiplier <=  maxPrime / 2; multiplier++)
            if (ctr * multiplier <= maxPrime)
               values.SetValue(1, ctr * multiplier);
      }      
      
      List<int> primes = new List<int>();
      for (int ctr = values.GetLowerBound(0); ctr <= values.GetUpperBound(0); ctr++)
         if ((int) values.GetValue(ctr) == 0) 
            primes.Add(ctr);
      return primes;
   }   
}
// The example displays the following output:
//    Primes less than 100:
//       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Remarks

If separator is null, an empty string (String.Empty) is used instead. If any member of values is null, an empty string is used instead.

Join<T>(String, IEnumerable<T>) is a convenience method that lets you concatenate each member of an IEnumerable<T> collection without first converting them to strings. The string representation of each object in the IEnumerable<T> collection is derived by calling that object's ToString method.

This method is particular useful with Language-Integrated Query (LINQ) query expressions. For example, the following code defines a very simple Animal class that contains the name of an animal and the order to which it belongs. It then defines a List<T> object that contains a number of Animal objects. The Enumerable.Where extension method is called to extract the Animal objects whose Order property equals "Rodent". The result is passed to the Join<T>(String, IEnumerable<T>) method.

using System;
using System.Collections.Generic;
using System.Linq;

public class Animal
{
   public string Kind;
   public string Order;
   
   public Animal(string kind, string order)
   {
      this.Kind = kind;
      this.Order = order;
   }
   
   public override string ToString()
   {
      return this.Kind;
   }
}

public class Example
{
   public static void Main()
   {
      List<Animal> animals = new List<Animal>();
      animals.Add(new Animal("Squirrel", "Rodent"));
      animals.Add(new Animal("Gray Wolf", "Carnivora"));
      animals.Add(new Animal("Capybara", "Rodent"));
      string output = String.Join(" ", animals.Where( animal => 
                      (animal.Order == "Rodent")));
      Console.WriteLine(output);  
   }
}
// The example displays the following output:
//      Squirrel Capybara

See also

Applies to

.NET 9 and other versions
Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

Join<T>(Char, IEnumerable<T>)

Source:
String.Manipulation.cs
Source:
String.Manipulation.cs
Source:
String.Manipulation.cs

Concatenates the members of a collection, using the specified separator between each member.

public static string Join<T> (char separator, System.Collections.Generic.IEnumerable<T> values);

Type Parameters

T

The type of the members of values.

Parameters

separator
Char

The character to use as a separator. separator is included in the returned string only if values has more than one element.

values
IEnumerable<T>

A collection that contains the objects to concatenate.

Returns

A string that consists of the members of values delimited by the separator character.

-or-

Empty if values has no elements.

Exceptions

values is null.

The length of the resulting string overflows the maximum allowed length (Int32.MaxValue).

Applies to

.NET 9 and other versions
Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Standard 2.1