Why is a string's byte size longer than the length? [closed]

问题

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.

Closed 6 years ago.

Why is it that sizeof("Bill") is 5 but sizeof(char) is 1?

Shouldn't that make sizeof("Bill") be 4 since the length of the string is 4 chars (4 x 1)?

I believe it may have something to do with "Bill" being an array of characters, but why does that increase the byte size?

回答1:

C strings are null terminated. There is a zero byte at the end of that string. Assuming ASCII, "Bill" looks like this in memory:

'B'  'i'  'l'  'l'  '\0'
0x42 0x69 0x6c 0x6c 0x00

From the C standard, Section 6.4.5 String literals, paragraph 7:

In translation phase 7, a byte or code of value zero is appended to each multibyte character sequence that results from a string literal or literals.

If you want to get an answer of 4 for the length, you should use strlen("Bill"), rather than sizeof.

If you really don't want the null-terminator, that's possible too, though probably ill-advised. This definition:

char bill[4] = "Bill";

will yield a 4-byte array bill containing just the characters 'B', 'i', 'l', and 'l', with no null-terminator.

回答2:

it has a 0 as a terminator character, so its B i l l 0

来源：https://stackoverflow.com/questions/16905877/why-is-a-strings-byte-size-longer-than-the-length