How are strings VS chars handled in C# vs Javascript?

Question

In JavaScript, single and double quotes are somewhat interchangeable and largely a matter of styles (There is a good discussion of why this isn't actually the case in one of the answers here: When to use double or single quotes in JavaScript?). How are chars and strings handled in C#?

For example:

string test = "hello world";
string test2 = 'hello world'; // Too many characters in character literal
char test3 = 'a';
char test4 = "a"; // Cannot implicitly convert type string to char

It looks like strings and chars are being handled as separate, interchangeable types, and that the use of single or double quotes demarcates this?

What is the relationship between chars and strings in typed languages? Specifically, would it be correct to say that a string is an array of chars?

Even "untyped" languages may handle strings and chars differently, especially when dealing with Unicode. You can't very well ask for the Unicode range of an entire string. Furthermore, each language handles strings differently from any other. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Jan 10, 2017 at 8:39
Strings aren't just arrays of chars. They are immutable, which means that you can't modify them as if they were just an array of chars. This allows the runtime to intern them and use a single instance of a string instead of creating copies. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Jan 10, 2017 at 8:40
Related: Single quotes vs. double quotes in C or C++ (Previous suggested duplicate was provided by a sub 3k user) — Sayse
– Sayse, Commented Jan 10, 2017 at 8:49

Patrick Hofman · Accepted Answer · 2017-01-10 08:41:52Z

5

would it be correct to say that a string is an array of chars

In .NET, a string is an object containing a contiguous block of memory containing UTF-16 code units. A char is another (primitive) data type that just contains one code point, with no object overhead.

From this interesting blog post from Jon Skeet, where he compares the .NET vs. Java implementation:

A long string consists of a single large object in memory. Compare this with Java, where a String is a “normal” type in terms of memory consumption, containing an offset and length into a char array – so a long string consists of a small object referring to a large char array.

answered Jan 10, 2017 at 8:41

Patrick Hofman

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8 Comments

Tim Schmelter Over a year ago

It's worth noting that you can treat a string like a char[] even in .NET, it has an indexer which you can use to access a char at a given index.

Patrick Hofman Over a year ago

Indeed. It mimics that very good, and that is why often people think it is an array of chars.

Keith Over a year ago

@TimSchmelter it is, hence my answer below.

Tim Schmelter Over a year ago

@Keith: your answer is still a bit misleading because there is no collection of chars in the string class, the indexer is implemented externally. As Patrick has said, it mimics a char[] (or collection of chars). ToCharArray also always creates a new one.

Tim Schmelter Over a year ago

@Keith: well, string.ToString is also a method but returns just this. A method is no guarantee that it doesn't use and return fields (or even the instance itself).

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Keith · Accepted Answer · 2017-01-10 09:58:45Z

2

C# uses the quotes to indicate the type - ' is always a char, " is always a string.

In .NET a string behaves like a read-only array of char, so:

// Treat string like an array
char c = "This is a string"[3];
int len = "This is a string".Length

// Now we have the char at pos 3
c == 's';

What you can't do is edit them:

// This fails
"This is a string"[3] = 'x';

// This is fine, because we get a new editable char[]
char[] c = "This is a string".ToCharArray();
c[3] = 'x';

This is true in any .NET language as they all use the same string implementation. Other strongly typed frameworks have different ways of handling strings.

In .NET char can be explicitly cast to an int and implicitly cast back, so:

char c = (char) 115; // 's'
int i = c; // 115

Finally char is a value type, while string (being a collection of character bytes under the covers) is actually an immutable reference type. These behave very similarly in code but are stored in different ways in memory - I think this is why C# makes the distinction in how they are delimited - "s" and 's' are different things and stored in different ways (entirely unlike the Javascript string).

edited Jan 10, 2017 at 9:58

answered Jan 10, 2017 at 8:51

Keith

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1 Comment

Keith Over a year ago

@TimSchmelter it's not a Collection<char> or anything like that - the indexer doesn't wrap a nested Array and internally it's just bytes. I think the indexer just copies the relevant pair of bytes.

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