String termination - char c=0 vs char c='\0'

Question

When terminating a string, it seems to me that logically char c=0 is equivalent to char c='\0', since the "null" (ASCII 0) byte is 0, but usually people tend to do '\0' instead. Is this purely out of preference or should it be a better "practice"?

What is the preferred choice?

EDIT: K&R says: "The character constant '\0' represents the character with value zero, the null character. '\0' is often written instead of 0 to emphasize the character nature of some expression, but the numeric value is just 0.

Hey Joe DF! Reading now K&R and had same question. Googled "\0 in c string" and second link is to your question. It helped me ;) — vasili111, Jul 24 '16 at 19:03

Nobilis · Accepted Answer · 2019-01-04T10:09:47.103

48

http://en.wikipedia.org/wiki/Ascii#ASCII_control_code_chart

Binary   Oct  Dec    Hex    Abbr    Unicode  Control char  C Escape code   Name
0000000  000  0      00     NUL     ␀       ^@            \0              Null character

There's no difference, but the more idiomatic one is '\0'.

Putting it down as char c = 0; could mean that you intend to use it as a number (e.g. a counter). '\0' is unambiguous.

edited Jan 04 '19 at 10:09

answered Jun 06 '13 at 07:21

Nobilis

7,310
1
33
67

1

Does the C standard guarantee ASCII? – Ciro Santilli OurBigBook.com Jun 27 '15 at 21:21
1

@CiroSantilli六四事件法轮功纳米比亚胡海峰 No, I'm looking at the C99 standard and there's a few footnotes that mention ASCII with respect to implementing trigraphs and language implementations in ASCII and that's it. It is something that's implementation defined (bear in mind character sets such as IBM's EBCDIC). But I think you'd struggle to find a modern C implementation that doesn't rely on the ASCII character set. There's some useful information relating to this [here](http://stackoverflow.com/questions/15251049/does-the-underlying-character-set-depend-only-on-the-c-implementation). – Nobilis Jun 28 '15 at 12:49
Yes, that's about what my read of the C99 gave as well. Thanks for that question, hadn't found it before. – Ciro Santilli OurBigBook.com Jun 28 '15 at 13:28
Especilally, in C/C++, 0 or '\0' also used to terminate the string literal, ex: "abc\0"+"def" will be "abc". This is a place where '\0' is more visually – Andiana Dec 06 '16 at 08:45

score 20 · Answer 2 · edited Jun 06 '13 at 07:32

20

'\0' is just an ASCII character. The same as 'A', or '0' or '\n'
If you write char c = '\0', it's the same aschar c = 0;
If you write char c = 'A', it's the same as char c = 65

It's just a character representation and it's a good practice to write it, when you really mean the NULL byte of string. Since char is in C one byte (integral type), it doesn't have any special meaning.

edited Jun 06 '13 at 07:32

Chris

44,602
16
137
156

answered Jun 06 '13 at 07:23

Michal Bukovy

422
3
16

2

or 0b1000001, or 0101, that's not important in my answer. It's all number. – Michal Bukovy Jun 06 '13 at 13:16
3

The character set doesn't have to be ASCII compatible, so 'A' does not have to be the same as 65. (E.g. EBCDIC is not ASCII compatible.) I don't know any character set that uses a non-zero value for the NUL character though. – Paul Groke Mar 21 '17 at 11:01
@PaulGroke Thanks for the comment! I wonder if there is a character set that uses a non-zero value for the null character. To note: 1) as Nobilis has mentioned: the C standard does not guarantee ASCII; 2) as Keith Thompson has mentioned (useful to know): the signedness of plain char is implementation-defined (source: https://stackoverflow.com/a/62682671/9881330). – pmor Jan 06 '21 at 23:02

score 6 · Answer 3 · answered Jun 06 '13 at 07:46

Preferred choice is that which can give people reading your code an ability to understand how do you use your variable - as a number or as a character. Best practice is to use 0 when you mean you variable as a number and to use '\0' when you mean your variable is a character.

score 0 · Answer 4 · answered Jul 26 '22 at 03:27

The above answers are already quite clear. I just share what I learned about this issue with a demo.

#include <stdlib.h>
#include <stdio.h>


char*
mystrcat(char *dest, char *src) {
    size_t i,j;
    for(i = 0; dest[i] != '\0'; i++)
        ;
    for(j = 0; src[j] != '\0'; j++)
        dest[i+j] = src[j];
    dest[i+j] = '\0';
    return dest;
}

int main() {
    char *str = malloc(20); // malloc allocate memory, but doesn't initialize the memory
    // str[0] = '\0'; 
    str[0] = 0;
    for (int k = 0; k <10; k++) {
        char s[2];
        sprintf(s, "%d", k);
        mystrcat(str, s);
    }
    printf("debug:%s\n", str);
    return 0;
}

In the above program, I used malloc to initialize the pointer, but malloc doesn't initialize the memory. So after the mystrcat operation(which is nearly the same as the strcat function in glibc), the string may contain mess code(since the memory content is not initialized).

So I need to initialize the memory. In this case str[0] = 0 and str[0] = 0 both can make it work.

String termination - char c=0 vs char c='\0'

4 Answers4

Linked