What Does {0} Mean When Found in a String in C#

What does {0} mean when found in a string in C#?

You are printing a formatted string. The {0} means to insert the first parameter following the format string; in this case the value associated with the key "rtf".

For String.Format, which is similar, if you had something like

//            Format string                    {0}           {1}
String.Format("This {0}.  The value is {1}.",  "is a test",  42 ) 

you'd create a string "This is a test. The value is 42".

You can also use expressions, and print values out multiple times:

//            Format string              {0} {1}  {2}
String.Format("Fib: {0}, {0}, {1}, {2}", 1,  1+1, 1+2) 

yielding "Fib: 1, 1, 2, 3"

See more at http://msdn.microsoft.com/en-us/library/txafckwd.aspx, which talks about composite formatting.

What does {0} stands for in Console.WriteLine?

As you can see, There's a code on your person object that returns a string, Console checks for If a type of string with name of ToString exists on your object class or not, If exists then It returns your string:

public override string ToString()
{
     return "Name = " + Name + ", Age = " + Age;
}

And {0} Is a formatted message, When you define It to {0} It means printing/formatting the zero Index object that you Inserted Into params arguments of your function. It's a zero based number that gets the index of object you want, Here's an example:

Console.WriteLine("{0} Is great, {1} Do you think of It? {2} Think {0} Is great!", "C#", "What", "I");

// C# Is great, What do you think of It? I think C# Is great!

When you say {0} It gets C# or the [0] of your object[].

C# - What does \0 equate to?

'\0' is a "null character". It's used to terminate strings in C and some portions of C++. Pex is doing a test to see how your code handles the null character, likely looking for the Poison Null Byte security exploit.

Most C# code has nothing to fear; if you pass your string to unmanaged code, however, you may have problems.

Edit:

Just to be explicit... Pex is passing a string containing a null character. This is not a null reference.

c# - What does {string[0]} mean?

GetRolesForUser returns an array of roles, so the "String[0]" in the immediate window just means that it knows the return type is an array (in this case strings), but there are zero entries (since no roles are returned for a blank user.

What does {0} mean in String.Format?

{0} is a placeholder for the first object given; in this case that's filename, so it will insert whatever filename evaluates to in place of {0}. Similarly, of course you could use {1} and that would be replaced with the second parameter passed, etc.

What does {0} mean in a string literal, for example in Console.WriteLine?

Also what is this feature called in C# I can't seem to locate it.

At the C# level: it isn't - because it isn't a C# feature at all; it is simply a library feature - see also string.Format. This handy utility method locates {0}, {1}, {2} etc and replaces them with the 0th, 1st, 2nd etc arguments. There is more to it that than, obviously (there are more complex formats available - patterns; negative vs positive, etc).

The documentation for Console.WriteLine is here: http://msdn.microsoft.com/en-us/library/828t9b9h.aspx

which links to "Composite Formatting": http://msdn.microsoft.com/en-us/library/txafckwd.aspx - which is what the BCL team call this, with intro:

The .NET Framework composite formatting feature takes a list of objects and a composite format string as input. A composite format string consists of fixed text intermixed with indexed placeholders, called format items, that correspond to the objects in the list. The formatting operation yields a result string that consists of the original fixed text intermixed with the string representation of the objects in the list.

What does this[0] mean in C#?

Look for an indexer in the class.

C# lets you define indexers to allow this sort of access.

Here is an example from the official guide for "SampleCollection".

public T this[int i]
    {
        get
        {
            // This indexer is very simple, and just returns or sets 
            // the corresponding element from the internal array. 
            return arr[i];
        }
        set
        {
            arr[i] = value;
        }
    }

Here is the definition from the official language specification:

An indexer is a member that enables objects to be indexed in the same way as an array. An indexer is declared like a property except that the name of the member is this followed by a parameter list written between the delimiters [ and ]. The parameters are available in the accessor(s) of the indexer. Similar to properties, indexers can be read-write, read-only, and write-only, and the accessor(s) of an indexer can be virtual.

One can find the full and complete definition in section 10.9 Indexers of the specification.

What does {0} mean when found in a key-value pair in C# config file?

For hard-coded strings that depend on user data, these sorts of configurations play very well with format strings. Your example configuration would be read and updated with

String.Format(uriUpdateProfile, variable0, variable1);

String.Format takes a large number of variables and repacles {0} and {1} with the passed in arguments. There are other ways to replicate this, and even simple replacements such as String.Replace("{0}", userID); could suffice.

Is there a concept of '\0' in C#?

Strings aren't null-terminated in C# (at least visibly; I believe they are internally for the sake of interop, but the termination character occurs outside the bounds of the string itself). The concept of the character '\0' (U+0000) does exist, but it can occur anywhere within a string - there's nothing special about it.

That means that your code to find '\0' does not find the length of the string. (It would also be simpler just to call str.IndexOf('\0') which will return -1 if the string doesn't contain U+0000.)

For example you could have:

string str = "a\0b";

That is a string of length 3 - but your code would claim it had a length of 1.

Just use the Length property to determine the length of a string (in UTF-16 code units; not necessarily Unicode characters). The length is stored in the String object separately from the text data; the Length property accesses it directly rather than having to iterate over the data.

What does (char)0 mean?

From the documentation:

TextBox.PasswordChar Property

[...]

The character used to mask characters entered in a single-line TextBox control. Set the value of this property to '0' (U+0000) if you do not want the control to mask characters as they are typed. The default value is '0' (U+0000).

U+0000 is the character at the Unicode code point 0, which is exactly what (char)0 in C# creates. Alternative ways to write this would be

txtPassword.PasswordChar = '\0';
txtPassword.PasswordChar = '\u0000';
txtPassword.PasswordChar = '\x0';

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