Function Using Pointers

[Eirik WS]

I have a function(whose code I have stolen from one of you
in comp.lang.c):

void myStringClean(c har *String) {
char *pointer;
if((pointer = strchr(String, '\n')) != NULL) {
*pointer = '\0';
}
}

How should I call this function? I've called like this in main.c:

myStringClean(m yName);
I get no errors or warnings when I call
the function like this with
gcc -ansi -pedantic -Wall -W,
when I call it using
myStringClean(& myName);
I get the warnings
passing arg 1 of 'myStringClean' from incompatible pointer type.

The prototype in mSC.h looks like this:
#include <string.h>

void myStringClean(c har *String);

In advance thanks for helpful replies.

--
No matches found

[Michael B Allen]

First, if you would like to receive replys to your question, I
recommend removing 'hannibalkannib alATyahooDOTno' from your news reader
configuration for the 'Followup-To' field.

On Mon, 05 Jan 2004 15:43:09 -0500, Eirik WS wrote:

when I call it using
myStringClean(& myName);
I get the warnings
passing arg 1 of 'myStringClean' from incompatible pointer type.

The declaration of myName is not 'char *myName;'. Perhaps you're using
'char myName[N];'?

Mike

[Christopher Benson-Manica]

Eirik WS <hx************ *************** ***@xyxaxhxoxox .no> spoke thus:

void myStringClean(c har *String) {
char *pointer;
if((pointer = strchr(String, '\n')) != NULL) {
*pointer = '\0';
}
} How should I call this function? I've called like this in main.c: myStringClean(m yName);
I get no errors or warnings when I call
the function like this with
gcc -ansi -pedantic -Wall -W,
I take this to indicate that myName is declared as

char myName[512]; /* or something */
when I call it using
myStringClean(& myName);
I get the warnings
passing arg 1 of 'myStringClean' from incompatible pointer type.

If my comment above is correct, then &myName is, indeed, incompatible
with your declaration of myStringClean. myStringClean takes a pointer
to a character as a parameter. myName is a pointer to a character, so
your first try works fine. &myName, though, is a pointer to a pointer
to a character, which is not the same thing. Say thank you to gcc for
kindly pointing this out to you.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Christopher Benson-Manica]

Christopher Benson-Manica <at***@nospam.c yberspace.org> spoke thus:

char myName[512]; /* or something */ If my comment above is correct, then &myName is, indeed, incompatible
with your declaration of myStringClean. myStringClean takes a pointer
to a character as a parameter. myName is a pointer to a character, so
your first try works fine. &myName, though, is a pointer to a pointer
to a character, which is not the same thing. Say thank you to gcc for
kindly pointing this out to you.

Um... let me just say that I expect and welcome comments about the
fact that I injudiciously called myName a pointer to a character...
*doh*

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Arthur J. O'Dwyer]

On Mon, 5 Jan 2004, Michael B Allen wrote:

On Mon, 05 Jan 2004 15:43:09 -0500, Eirik WS wrote:

when I call it using
myStringClean(& myName);
I get the warnings
passing arg 1 of 'myStringClean' from incompatible pointer type.

The declaration of myName is not 'char *myName;'. Perhaps you're using
'char myName[N];'?

No, his function was prototyped to take a 'char *', that is to say
a string. So he should be writing

char *mystring = foo();
myStringClean(m ystring); /* note no '&' anywhere */

He could also write

char mystring[] = "something else";
myStringClean(m ystring); /* note no '&' anywhere */

of course, but the problem in the code you left quoted isn't with
the variable declarations or the function implementation -- it's
with the way he was trying to call the function.
Given that the OP noticed that the first way worked and the
second way didn't, I don't think there's much more to add.

-Arthur

[Arthur J. O'Dwyer]

On Mon, 5 Jan 2004, Christopher Benson-Manica wrote:

Christopher Benson-Manica <at***@nospam.c yberspace.org> spoke thus:

char myName[512]; /* or something */

If my comment above is correct, then &myName is, indeed, incompatible
with your declaration of myStringClean. myStringClean takes a pointer
to a character as a parameter. myName is a pointer to a character, so
your first try works fine. &myName, though, is a pointer to a pointer
to a character, which is not the same thing. Say thank you to gcc for
kindly pointing this out to you.

Um... let me just say that I expect and welcome comments about the
fact that I injudiciously called myName a pointer to a character...
*doh*

No, the expression 'myName' *does* yield a pointer to character in
this context. You're going to get comments about the fact that you
called '&myName' a "pointer to a pointer to a character," when it's
really a pointer to an array[512] of character. :)

-Arthur

[Al Bowers]

Eirik WS wrote:

What is Follow-up to: hannibalkanniba lATyahooDOTno?
Are you playing games?

I have a function(whose code I have stolen from one of you
in comp.lang.c):

void myStringClean(c har *String) {
char *pointer;
if((pointer = strchr(String, '\n')) != NULL) {
*pointer = '\0';
}
}
This is not a robost function. It simply searches the
string pointed to by the argument, from first char to last,
looking for the first occurance of '\n', the newline character.
If it finds a newline character, it will overwrite it with '\0'
which truncates the string and then the function will exit. It a
newline character is not found, the string remains unchanged.
IMO it is a poorly written function, especially because it does
not return a value indicating whether or not the string was
modified.
How should I call this function? I've called like this in main.c:

myStringClean(m yName);
I get no errors or warnings when I call
the function like this with
gcc -ansi -pedantic -Wall -W,
when I call it using
myStringClean(& myName);
I get the warnings
passing arg 1 of 'myStringClean' from incompatible pointer type.

You did not provide the declaration of myName. myName and &myName
are not the same. You would think that one or the other is wrong.

The prototype in mSC.h looks like this:
#include <string.h>

void myStringClean(c har *String);

Here is an example of the use of this function.

#include <stdio.h>
#include <string.h>

/* prototype */
void myStringClean(c har *String);

int main(void)
{
char string[64] = "This is line one\nThis is line two";

puts("Before calling function myStringClean") ;
printf("The string = \"%s\"\n",strin g);

myStringClean(s tring);

puts("\nAfter calling function myStringClean") ;
printf("The string = \"%s\"\n",strin g);
return 0;
}

void myStringClean(c har *String)
{
char *pointer;
if((pointer = strchr(String, '\n')) != NULL)
*pointer = '\0';
}
--
Al Bowers
Tampa, Fl USA
mailto: xa******@myrapi dsys.com (remove the x to send email)
http://www.geocities.com/abowers822/

[Christopher Benson-Manica]

Arthur J. O'Dwyer <aj*@nospam.and rew.cmu.edu> spoke thus:

No, the expression 'myName' *does* yield a pointer to character in
this context. You're going to get comments about the fact that you
called '&myName' a "pointer to a pointer to a character," when it's
really a pointer to an array[512] of character. :)

Now, you say 'myName' "yields" a pointer to a character - I do know
that it decays to such in this context - but is it *really* a pointer
to a character? Is that too pedantic of a question? The faqt (sic)
is that this is a FAQ and I blew it, although I did retrieve my error
in a timely fashion, kind of.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Eric Sosman]

Eirik WS wrote:

I have a function(whose code I have stolen from one of you
in comp.lang.c):

void myStringClean(c har *String) {
char *pointer;
if((pointer = strchr(String, '\n')) != NULL) {
*pointer = '\0';
}
}

How should I call this function? I've called like this in main.c:

myStringClean(m yName);
I get no errors or warnings when I call
the function like this with
gcc -ansi -pedantic -Wall -W,
when I call it using
myStringClean(& myName);
I get the warnings
passing arg 1 of 'myStringClean' from incompatible pointer type.

The prototype in mSC.h looks like this:
#include <string.h>

void myStringClean(c har *String);

In advance thanks for helpful replies.

You have omitted one crucial piece of information: the
declaration of `myName'. However, since gcc accepts the first
form of the call without complaint it appears `myName' is
either a `char' array or a pointer to `char'. Read Section 6
in the comp.lang.c Frequently Asked Questions (FAQ) list

http://www.eskimo.com/~scs/C-faq/top.html

.... if you are confused about why I cannot tell whether
`myName' is an array or a pointer from the information you
have provided.

The second form of the call is incorrect because:

- If `myName' is an array of `char', then `&myName'
is a pointer to such an array. myStringClean() ,
though, expects to receive a pointer to a `char',
not a pointer to an array -- and that is why gcc
complains. See FAQ Questions 6.12 and 6.13.

- If `myName' is a `char*' pointer variable, then
`&myName' is a pointer to a pointer (... to `char').
myStringClean() expects to receive a pointer to a
`char', not a pointer to a pointer, so gcc complains.

--
Er*********@sun .com

[Joona I Palaste]

Christopher Benson-Manica <at***@nospam.c yberspace.org> scribbled the following:

Arthur J. O'Dwyer <aj*@nospam.and rew.cmu.edu> spoke thus:

No, the expression 'myName' *does* yield a pointer to character in
this context. You're going to get comments about the fact that you
called '&myName' a "pointer to a pointer to a character," when it's
really a pointer to an array[512] of character. :)

Now, you say 'myName' "yields" a pointer to a character - I do know
that it decays to such in this context - but is it *really* a pointer
to a character? Is that too pedantic of a question? The faqt (sic)
is that this is a FAQ and I blew it, although I did retrieve my error
in a timely fashion, kind of.

Depends on what do you mean by "myName". The variable myName or the
expression consisting of it? They're two very different beasts.

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"My absolute aspect is probably..."
- Mato Valtonen