' vs " while using chars, in C

Question

So I've been trying to use strcat like this lately and I've always got an error:

strcat(string, 'a');

And then I realised that I have to use something which contains '\0' as the second parameter, in order to have a const char* .

Well, I was just playing around in VS, and using strcat like this:

strcat(string, "a");

rendered no error.

This is very strange to me, because some days ago I've learnt that I need to create an auxiliary char, like this:

aux[0] = 'a';
aux[1] = '\0';
strcat(string, aux);

if I wanted to add only a character to a string.

Now I'm a bit lost to be honest.

Can anybody explain what's the difference between ' and " when using chars?

Thanks.

Single quotes for single characters. Double quotes for null.terminated strings. And in C a single character is usually implicitly converted to `int` values, and null terminated strings are really arrays of characters (including the terminator). A literal string (using double-quotes, like e.g. `"a"`) is an array of non-modifiable (read-only) characters. — Some programmer dude, May 14 '20 at 16:53

score 3 · Answer 1 · answered May 14 '20 at 16:55

3

String literals are implicitly null-terminated. These are equivalent declarations:

const char a[] = "a";
const char a[] = { 'a', '\0' };

answered May 14 '20 at 16:55

Carl Norum

219,201
40
422
469

Thanks. The example made me better understand. – Octavian Niculescu May 14 '20 at 17:01

score 3 · Answer 2 · edited May 14 '20 at 17:38

3

' (single quote) is for creating a single character which is almost the same thing as an integer.

On the other hand " (double quote) is used for creating a constant char pointer which means a memory block that is terminated with a null and contains characters in it.

You can put as many characters as you want in double quotes, but ' will always contain a single character.

Also you cannot compare double quoted strings for equality because, in the end of the day, what it creates is a pointer which is the starting point of your string which is a 32 or 64 bit integer on most machines. On the other hand comparing chars (single quoted) is fine because they are values themselves rather then being pointers to addresses.

edited May 14 '20 at 17:38

Roberto Caboni

7,252
10
25
39

answered May 14 '20 at 16:57

nikoss

3,254
2
26
40

1

Thanks a lot for your in-depth answer. Now I get it. – Octavian Niculescu May 14 '20 at 17:02
A `char` is an integer, not almost the same thing as one, right? – Fiddling Bits May 14 '20 at 17:02
@FiddlingBits actually a char is a byte it is 8 bits on most machines where an int is likely to be 64 or 32 bits I just didnt want to make more confusion by talking about bytes and stuff in a beginner question – nikoss May 14 '20 at 17:08

' vs " while using chars, in C

2 Answers2