How do I interpolate strings?

Question

I want to do the following in C# (coming from a Python background):

strVar = "stack"
mystr  = "This is %soverflow" % (strVar)

How do I replace the token inside the string with the value outside of it?

Answer 1

This has been added as of C# 6.0 (Visual Studio 2015+).

Example:

var planetName = "Bob";
var myName = "Ford"; 
var formattedStr = $"Hello planet {planetName}, my name is {myName}!";
// formattedStr should be "Hello planet Bob, my name is Ford!"

This is syntactic sugar for:

var formattedStr = String.Format("Hello planet {0}, my name is {1}!", planetName, myName);

Additional Resources:

String Interpolation for C# (v2) Discussion

C# 6.0 Language Preview

Answer 2

string mystr = string.Format("This is {0}overflow", strVar);

And you could also use named parameters instead of indexes.

Answer 3

You can use string.Format to drop values into strings:

private static readonly string formatString = "This is {0}overflow";
...
var strVar = "stack";
var myStr = string.Format(formatString, "stack");

An alternative is to use the C# concatenation operator:

var strVar = "stack";
var myStr = "This is " + strVar + "overflow";

If you're doing a lot of concatenations use the StringBuilder class which is more efficient:

var strVar = "stack";
var stringBuilder = new StringBuilder("This is ");
for (;;)
{
    stringBuilder.Append(strVar); // spot the deliberate mistake ;-)
}
stringBuilder.Append("overflow");
var myStr = stringBuilder.ToString();

Answer 4

If you currently use Visual Studio 2015 with C# 6.0, try the following:

var strVar = "stack";

string str = $"This is {strVar} OverFlow";

that feature is called string interpolation.

Answer 5

C# 6.0

string mystr = $"This is {strVar}overflow";

Answer 6

There is no operator for that. You need to use string.Format.

string strVar = "stack";
string mystr  = string.Format("This is {0}soverflow", strVar);

Unfortunately string.Format is a static method, so you can't simply write "This is {0}soverflow".Format(strVar). Some people have defined an extension method, that allows this syntax.

Answer 7

Use string.Format:

string mystr = string.Format("This is {0}overflow", "stack");

Answer 8

You should be using String.Format(). The syntax is a bit different, numerical placeholders are used instead.

Example:

String.Format("item {0}, item {1}", "one", "two")

Have a look at http://msdn.microsoft.com/en-us/library/system.string.format.aspx for more details.

Answer 9

You have 2 options. You can either use String.Format or you can use the concatenation operator.

String newString = String.Format("I inserted this string {0} into this one", oldstring);

OR

String newString = "I inserted this string " + oldstring + " into this one";