char arrays length in C

Question

In C, you have to declare the length of an array:

int myArray[100];

But when you're dealing with chars and strings, the length can be left blank:

char myString[] = "Hello, World!";

Does the compiler generate the length for you by looking at the string?

You don't have to explicitly declare the length of an `int` array either: `int a[] = {1,2,3};` — mhyfritz, Jun 27 '11 at 18:15
All answers are correct, all upvoted. I always feel silly when I can't decide which answer is the best. — , Jun 27 '11 at 18:16

score 10 · Answer 1 · edited Apr 15 '12 at 13:00

10

Yes, it's the length including the terminating '\0'.

edited Apr 15 '12 at 13:00

answered Jun 27 '11 at 18:13

Karoly Horvath

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score 10 · Accepted Answer · answered Jun 27 '11 at 18:14

10

This is not unique to char. You could do this, for instance:

int myNumbers[] = { 5, 10, 15, 20, 42 };

This is equivalent to writing:

int myNumbers[5] = { 5, 10, 15, 20, 42 };

Initialising a char array from a string literal is a special case.

answered Jun 27 '11 at 18:14

Oliver Charlesworth

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score 5 · Answer 3 · answered Jun 27 '11 at 18:13

5

Does the compiler generate the length for you by looking at the string?

Yes, that's exactly why it works. The compiler sees the constant value, and can fill in the length so you don't have to do it.

answered Jun 27 '11 at 18:13

Reed Copsey

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score 3 · Answer 4 · answered Jun 27 '11 at 18:14

3

Yes, the compiler knows the length of the string and allocates the appropriate space.

answered Jun 27 '11 at 18:14

The Archetypal Paul

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score 3 · Answer 5 · edited Jun 27 '11 at 18:18

3

It's the same deal if you did something like...

int x[] = {1,2,3};

edited Jun 27 '11 at 18:18

answered Jun 27 '11 at 18:17

MGZero

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score 2 · Answer 6 · answered Jun 27 '11 at 18:47

The size of the string literal (not length as in strlen) is used to size the array being initialized.

You can initialize a char array with a string literal which has embedded null bytes. The resulting array will have size for all the bytes after the first (or second, ...) null.

char array[] = "foo\0bar\0baz\0quux";
/* sizeof array is 17
** array[3] is 0
** printf("%s\n", array + 4); prints bar
** array[11] is 0
** printf("%s\n", array + 12); prints quux
** array[16] == 0
*/

char arrays length in C

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