Difference between '\0' and 0

[August Karlstrom]

Hello all,

If c is a char then is there any difference between

c = '\0'

and

c = 0

?
Regards,
August

[pete]

August Karlstrom wrote:

Hello all,

If c is a char then is there any difference between

c = '\0'

and

c = 0

?

It doesn't matter what c is.
'\0' and 0 are both constant primary expressions
of type int and value zero.

--
pete

[yohji]

August Karlstrom wrote:

Hello all,

If c is a char then is there any difference between

c = '\0'

and

c = 0

?
Regards,
August

Er,in fact,in C, a char is an 8-bit integer(not all).The ASCII value of
'\0' is 0.So c='\0' equals to c=0 .In many programs,we use char instead
of int when the integer is small.

[August Karlstrom]

pete wrote:

August Karlstrom wrote:

Hello all,

If c is a char then is there any difference between

c = '\0'

and

c = 0

?

It doesn't matter what c is.
'\0' and 0 are both constant primary expressions
of type int and value zero.

The Lint program Splint thinks there is a difference:

$ cat test.c
int main(void)
{
char c;

c = '\0';
c = 0;
return 0;
}
$ splint test.c
Splint 3.1.1 --- 15 Jun 2004

test.c: (in function main)
test.c:6:4: Assignment of int to char: c = 0
Types are incompatible. (Use -type to inhibit warning)

Finished checking --- 1 code warning
-- August

[Martin Ambuhl]

yohji wrote:

Er,in fact,in C, a char is an 8-bit integer(not all).The ASCII value of
'\0' is 0.So c='\0' equals to c=0 .In many programs,we use char instead
of int when the integer is small.

1) In fact, '\0' is an int, not a char, so it the question of chars
doesn't enter into the question.

2) In fact, a char is *not* an 8-bit integer. It is an integral type
capable of representing one of the two ranges CHAR_MIN to CHAR_MAX (if
char is signed) or 0 to UCHAR_MAX (if char is unsigned). The minimum
size on a binary machine to be able to meet that for the minimal
requirements of the standard is 8 bits.

3) In fact, the ASCII value of anything is irrelevant in comp.lang.c,
where we expect programs to be appropriate for any environment that
meets the requirements for the source and execution character sets in
the corresponding contexts. There is nothing special about ASCII, which
is only one of many encodings.

[Malcolm]

"August Karlstrom" <fu********@com hem.se> wrote

It doesn't matter what c is.
'\0' and 0 are both constant primary expressions
of type int and value zero.

The Lint program Splint thinks there is a difference:

test.c:6:4: Assignment of int to char: c = 0
Types are incompatible. (Use -type to inhibit warning)

Lint is of limited value. '\0' is the character constant NUL that represents
a terminated string, whilst 0 is the integer value of nothing. However '\0'
== 0 is guaranteed to be true.
In fact use of a four character sequence doesn't add much to program
readbility, and may detract from it. Most code uses plain 0. It is also
quite common to see the construct

while(*str)
{
/* some code */
str++;
}

If you want strict type control, use a different language to C. C written to
make lint happy tends to be C that is hard to read.

[Lawrence Kirby]

On Sat, 28 May 2005 22:36:32 +0000, Martin Ambuhl wrote:

yohji wrote:

Er,in fact,in C, a char is an 8-bit integer(not all).The ASCII value of
'\0' is 0.So c='\0' equals to c=0 .In many programs,we use char instead
of int when the integer is small.

1) In fact, '\0' is an int, not a char, so it the question of chars
doesn't enter into the question.

2) In fact, a char is *not* an 8-bit integer. It is an integral type
capable of representing one of the two ranges CHAR_MIN to CHAR_MAX (if
char is signed)

It is CHAR_MIN to CHAR_MAX whether char is signed or unsigned. This
corresponds to SCHAR_MIN to SCHAR_MAX when char is signed.

Lawrence

[August Karlstrom]

Malcolm wrote:

Lint is of limited value. '\0' is the character constant NUL that represents
a terminated string, whilst 0 is the integer value of nothing.
(The literal 0 can also denote the nil pointer)
However '\0' == 0 is guaranteed to be true.
In fact use of a four character sequence doesn't add much to program
readbility, and may detract from it. Most code uses plain 0. It is also
quite common to see the construct

while(*str)
{
/* some code */
str++;
}

If you want strict type control, use a different language to C. C written to
make lint happy tends to be C that is hard to read.

Ok, I tend to agree.
-- August

[Dik T. Winter]

In article <Pg************ *******@newsb.t elia.net> August Karlstrom <fu********@com hem.se> writes:
....

$ cat test.c
int main(void)
{
char c;

c = '\0';
c = 0;
return 0;
}
$ splint test.c
Splint 3.1.1 --- 15 Jun 2004

test.c: (in function main)
test.c:6:4: Assignment of int to char: c = 0
Types are incompatible. (Use -type to inhibit warning)

It is a bug that it does not complain about c = '\0'. In that case the
types are also "incompatib le". But the mindset of the writers can be
deduced from the following in the known bugs file:
Pre-processing ISO8859-1 characters
Splint does not process ISO8859-1 characters correctly since it is
building on a pre-ISO8859-1 version of gcc's pre-processor, and
character \377 is indistinguishab le from EOF.

'\377' is an intr with value 255, so quite distinguishable from EOF, which
is also an int. The conclusion is that Splint does not handle character
constants correctly.
--
dik t. winter, cwi, kruislaan 413, 1098 sj amsterdam, nederland, [phone]
home: bovenover 215, 1025 jn amsterdam, nederland; http://www.cwi.nl/~dik/

[Keith Thompson]

August Karlstrom <fu********@com hem.se> writes:

pete wrote:

August Karlstrom wrote:

Hello all,
If c is a char then is there any difference between
c = '\0'
and
c = 0
?

It doesn't matter what c is.
'\0' and 0 are both constant primary expressions
of type int and value zero.

The Lint program Splint thinks there is a difference:

$ cat test.c
int main(void)
{
char c;

c = '\0';
c = 0;
return 0;
}
$ splint test.c
Splint 3.1.1 --- 15 Jun 2004

test.c: (in function main)
test.c:6:4: Assignment of int to char: c = 0
Types are incompatible. (Use -type to inhibit warning)

Finished checking --- 1 code warning

The difference is only stylistic; there is absolutely no difference as
far as the language is concerned. I consider
c = '\0';
to be clearer than
c = 0;
because it implies to the reader (though not to the compiler) that a
character value is being assigned. Apparently the authors of splint
felt the same way.

Since a character constant, unlike an integer constant, normally can't
have a value outside the range of type char, it's not unreasonable for
splint to treat it as being of type char. But since even a reference
to a char object:
char c = '\0';
char x = c;
is promoted to int before being converted back to char, it's difficult
to know just what's going to keep splint from complaining.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.