CODEWITHSUNDEEP
cnul
Paul
Paul

Reputation: 141877

Is '\0' guaranteed to be 0?

I wrote this function in C, which is meant to iterate through a string to the next non-white-space character:

char * iterate_through_whitespace(unsigned char * i){
    while(*i && *(i++) <= 32);
    return i-1;
}

It seems to work quite well, but I'm wondering if it is safe to assume that the *i will be evaluated to false in the situation that *i == '\0', and it won't iterate beyond the end of a string. It works well on my computer, but I'm wondering if it will behave the same when compiled on other machines.

Upvotes: 21

Views: 739

Answers (5)

OTheDev
OTheDev

Reputation: 2965

I find the other answers inadequate because they do not provide a direct answer to the question in the title.

Is '\0' guaranteed to be 0?

No, the integer value of the construction '\0' is not guaranteed to be 0 by the C standard.

Regarding the null character, all we know is that (C99 p.17, C11 p.22)

[a] byte with all bits set to 0, called the null character, shall exist in the basic execution set.

and that (C99 p. 61, C11 p.69)

[t]he construction '\0' is commonly used to represent the null character.

Emphasis on "commonly used". There is no guarantee.

Upvotes: 0

R.. GitHub STOP HELPING ICE
R.. GitHub STOP HELPING ICE

Reputation: 215387

In C, '\0' has the exact same value and type as 0. There is no reason to ever write '\0' except to uglify your code. \0 might however be useful inside double quotes to make strings with embedded null bytes.

Upvotes: 3

zneak
zneak

Reputation: 138171

The ASCII standard dictates that the NUL character is encoded as the byte 0. Unless you stop working with encodings that are backwards compatible with ASCII, nothing should go wrong.

Upvotes: 0

Keith Thompson
Keith Thompson

Reputation: 263497

Yes -- but in my opinion it's better style to be more explicit:

while (*i != '\0' && ...

But the comparison to 32 is hardly the best approach. 32 happens to be the ASCII/Unicode code for the space character, but C doesn't guarantee any particular character set -- and there are plenty of control characters with values less than 32 that aren't whitespace.

Use the isspace() function.

(And I'd never name a pointer i.)

Upvotes: 14

cnicutar
cnicutar

Reputation: 182664

The standard says:

A byte with all bits set to 0, called the null character, shall exist in the basic execution character set; it is used to terminate a character string.

Upvotes: 16

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