Counting occurence of character in a string

[Michael McGarry]

Hi,

Is there a standard library function that counts the number of
occurences of a character in a string?

Regards,

Michael

 

[pete]

Hi,

Is there a standard library function that counts the number of
occurences of a character in a string?

No.

 

[Peter Nilsson]

No.

If it were, it would probably be implemented along the lines of...

size_t strccnt(const char *s, int c)
{
const unsigned char *us = (const unsigned char *) s;
const unsigned char uc = c;
size_t n = 0;
if (!uc) return 1;
while (*us) if (*us++ == uc) n++;
return n;
}

 

[Barry Schwarz]

Hi,

Is there a standard library function that counts the number of
occurences of a character in a string?

No


<<Remove the del for email>>

 

[=?ISO-8859-1?Q?Bj=F8rn_Augestad?=]

If it were, it would probably be implemented along the lines of...

size_t strccnt(const char *s, int c)
{
const unsigned char *us = (const unsigned char *) s;
const unsigned char uc = c;
size_t n = 0;
if (!uc) return 1;

return 1 ?

while (*us) if (*us++ == uc) n++;
return n;
}

What's wrong with a simpler version?
size_t strccnt(const char* s, int c)
{
size_t n = 0;

while(*s != '\0') {
if(*s++ == c)
n++;
}

return n;
}


Bjørn

 

[Skarmander]

If it were, it would probably be implemented along the lines of...

size_t strccnt(const char *s, int c)
{
const unsigned char *us = (const unsigned char *) s;
const unsigned char uc = c;
size_t n = 0;
if (!uc) return 1;

<snip>

I'd argue for "return 0", or rather, omitting the check altogether. The
NUL character does not occur in the string. That would be more something
for a "memccnt" function.

S.

 

[Jordan Abel]

<snip>

I'd argue for "return 0", or rather, omitting the check altogether. The
NUL character does not occur in the string.

Traditionally, the NUL character appears exactly once, at the end of the
string, and this location is returned in strchr/strrchr.

 

[pete]

Traditionally,
the NUL character appears exactly once, at the end of the
string, and this location is returned in strchr/strrchr.

N869
7. Library
7.1 Introduction
7.1.1 Definitions of terms
[#1] A string is a contiguous sequence of characters
terminated by and including the first null character.

 

[Michael McGarry]

Thanks to all for your help.

 

[Skarmander]

Traditionally, the NUL character appears exactly once, at the end of the
string, and this location is returned in strchr/strrchr.

You're right. 7.1.1. "A string is a contiguous sequence of characters
terminated by and including the first null character." This means that a
string is considered to include NUL except where stated otherwise. 1 is
the correct answer. (But I'd make it explicit in the function's
description.)

S.

 

[Randy Howard]

Bjørn Augestad wrote

What's wrong with a simpler version?
size_t strccnt(const char* s, int c)

Apart from namespace problems? Not much.

 

[David Resnick]

Bjørn Augestad wrote


Apart from namespace problems? Not much.

If you read upthread, Peter Nilsson had posited
his function (with the name strccnt) as how the implementation
would name/code such a function if it were in the standard
library. So in that context the name is fine

-David

 

[Jordan Abel]

Bjørn Augestad wrote


Apart from namespace problems? Not much.

It's fine on a freestanding implementation

 

[Keith Thompson]

You're right. 7.1.1. "A string is a contiguous sequence of characters
terminated by and including the first null character." This means that
a string is considered to include NUL except where stated otherwise. 1
is the correct answer. (But I'd make it explicit in the function's
description.)

Yes, just as it's explicit in the standard's description of strchr()
and strrchr().

 

[Randy Howard]

Jordan Abel wrote

It's fine on a freestanding implementation

Contact slashdot, new news at 11.

 

[Old Wolf]

return 1 ?

1 occurrence of 0 in the string.

What's wrong with a simpler version?
size_t strccnt(const char* s, int c)
{
size_t n = 0;
while(*s != '\0') {
if(*s++ == c)
n++;
}
return n;
}

Your version works for CHAR_MIN <= c <= CHAR_MAX.
Peter's version works for CHAR_MIN <= c <= UCHAR_MAX.

So his version could safely be called like this:
int ch = getchar();
strccnt(s, ch);
as well as
strccnt(s, 'é');

The functions in <ctype.h> and <stdio.h> expect a value
in the range 0 <= c <= UCHAR_MAX.

 

[Peter Nilsson]

It's fine on a freestanding implementation

Do you have chapter and verse on that?

 

[=?ISO-8859-1?Q?Bj=F8rn_Augestad?=]

1 occurrence of 0 in the string.

First I read that as if(!us), not if(!uc) and was wondering why the
function returned 1 when it received a NULL pointer. My mistake.

Your version works for CHAR_MIN <= c <= CHAR_MAX.
Peter's version works for CHAR_MIN <= c <= UCHAR_MAX.

So his version could safely be called like this:
int ch = getchar();
strccnt(s, ch);
as well as
strccnt(s, 'é');

The functions in <ctype.h> and <stdio.h> expect a value
in the range 0 <= c <= UCHAR_MAX.

You,re right, thanks. (Why can't we all use ASCII only? ;-) )

Bj&oring;rn

 

[pete]

1 occurrence of 0 in the string.


Your version works for CHAR_MIN <= c <= CHAR_MAX.

It doesn't work when c equals zero.

Peter's version works for CHAR_MIN <= c <= UCHAR_MAX.

I don't see the point in searching for values
outside the range of char, in an array of char,
and neither does strchr.
I think it's more better to compare *s against
the value of c converted to type char,
as in the standard's description of strchr.

size_t str_ccnt(const char* s, int c)
{
size_t n = 0;

do {
if (*s == (char)c) {
n++;
}
} while(*s++ != '\0');
return n;
}

strcmp and strncmp are the only standard string functions
which are based on unsigned char interpretation of bytes.
All of the others, like strchr, are based on char values.
I think strccnt should be more like strchr, than like strcmp.

 

[pete]

Do you have chapter and verse on that?

Jordan Abel has an intense desire
to find some context in which it is OK
to use reserved identifiers to name his functions.
I don't know why.