char*& and char* ???

[pembed2003]

Hi coders,
I have the following:

void f1(char* &s){
*s = 'a';
}

void f2(char* s){
*s = 'b';
}

int main(int argc,char** argv){
char a[] = "1234";
char* b = a;
printf("%s\n",a);
f1(b);
printf("%s\n",a);
f2(b);
printf("%s\n",a);
return 0;
}

The above prints:

1234
a234
b234

My question is:

1. How is char*& different from char* since they both do the same thing?
2. When do you use the first form and the second form?

Thanks!

[Malcolm]

"pembed2003" <pe********@yahoo.com> wrote in message

1. How is char*& different from char* since they both do the same > thing?
char *& is C++ and ia a pointer passed by reference. char * is C and is just
a pointer.
2. When do you use the first form and the second form?

First form when programming in C++. You need to ask in clc++ about when it
is appropriate to use references and when to use pointers.
You would use the second form whenever you want to pass an array of
characters (eg a string) to a C function, and in a few other cases.

[Martin Ambuhl]

pembed2003 wrote:

Hi coders,
I have the following:

void f1(char* &s){ ^^^^^^^^
syntax error
[...]

1. How is char*& different from char*
'char*&' is a syntax error, 'char*' isn't.
since they both do the same thing?
No they don't.
2. When do you use the first form
Never
and the second form?

When you need a pointer to char

[pembed2003]

Martin Ambuhl <ma*****@earthlink.net> wrote in message news:<c5************@ID-227552.news.uni-berlin.de>...

pembed2003 wrote:

Hi coders,
I have the following:

void f1(char* &s){ ^^^^^^^^
syntax error
[...]

I compile the code using gcc but it doesn't produce any error. do you
know why? Is gcc a C compiler?

1. How is char*& different from char*
'char*&' is a syntax error, 'char*' isn't.

since they both do the same thing?

No they don't.

sorry. i mean that they do the same thing in the sample program I
posted.

2. When do you use the first form

Never

Why?

and the second form?

When you need a pointer to char

Thanks!

[Martin Ambuhl]

pembed2003 wrote:

Martin Ambuhl <ma*****@earthlink.net> wrote in message news:<c5************@ID-227552.news.uni-berlin.de>...

pembed2003 wrote:

Hi coders,
I have the following:

void f1(char* &s){
^^^^^^^^
syntax error
[...]

I compile the code using gcc but it doesn't produce any error. do you
know why? Is gcc a C compiler?

You didn't invoke gcc properly.
suppost your program is named a.c
Try one of
gcc -Wall -W -std=c89 -pedantic a.c
gcc -Wall -W -ansi -pedantic a.c
gcc -Wall -W -std=c99 -pedantic a.c

1. How is char*& different from char*
'char*&' is a syntax error, 'char*' isn't.

since they both do the same thing?

No they don't. sorry. i mean that they do the same thing in the sample program I
posted.

They don't do the same thing, period. 'char* &' is a syntax error which
gcc, when properly invoked, is reported as a parsing error. It is
impossible for a syntax error to predictably have the same effect as
legal code. The most likely result of syntax error is a compilation
failure.

2. When do you use the first form

Never

Why?

If you don't get this, you are truly an idiot.

[Stephen Sprunk]

"pembed2003" <pe********@yahoo.com> wrote in message
news:db**************************@posting.google.c om...

Hi coders,
I have the following:

void f1(char* &s){
*s = 'a';
}
That looks like C++; it's not valid C.
void f2(char* s){
*s = 'b';
}

That is valid C.

S

--
Stephen Sprunk "Stupid people surround themselves with smart
CCIE #3723 people. Smart people surround themselves with
K5SSS smart people who disagree with them." --Aaron Sorkin

[Martin Dickopp]

pe********@yahoo.com (pembed2003) writes:

Is gcc a C compiler?

No. GCC stands for "GNU Compiler Collection". The collection currently
includes compilers for C, C++, Objective C, Java, Fortran, and Ada.

Martin
--
,--. Martin Dickopp, Dresden, Germany ,= ,-_-. =.
/ ,- ) http://www.zero-based.org/ ((_/)o o(\_))
\ `-' `-'(. .)`-'
`-. Debian, a variant of the GNU operating system. \_/

[Christian Bau]

In article <db**************************@posting.google.com >,
pe********@yahoo.com (pembed2003) wrote:

Martin Ambuhl <ma*****@earthlink.net> wrote in message
news:<c5************@ID-227552.news.uni-berlin.de>...

pembed2003 wrote:

Hi coders,
I have the following:

void f1(char* &s){

^^^^^^^^
syntax error
[...]

I compile the code using gcc but it doesn't produce any error. do you
know why? Is gcc a C compiler?

I should really hope that you know which language your compiler is
compiling. Read the documentation.

Try compiling this:

int main (void)
{
int new = 0;
int class = 0;
return new + class;
}

and see what your compiler thinks about it.

[Keith Thompson]

pe********@yahoo.com (pembed2003) writes:

Martin Ambuhl <ma*****@earthlink.net> wrote in message
news:<c5************@ID-227552.news.uni-berlin.de>...

pembed2003 wrote:

Hi coders,
I have the following:

void f1(char* &s){

^^^^^^^^
syntax error
[...]

I compile the code using gcc but it doesn't produce any error. do you
know why? Is gcc a C compiler?

It can be; it can also be a C++ compiler. It typically decides which
frontend to invoke based on the suffix on the file name. If your
source file has a name ending in ".c", gcc should correctly report a
syntax error on the above; if it ends in ".C" or ".cc", it will assume
it's C++, and behave in a manner that we're not qualified to discuss
in this newsgroup.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"

[Dan Pop]

In <db**************************@posting.google.com > pe********@yahoo.com (pembed2003) writes:

Hi coders,
I have the following:

void f1(char* &s){
*s = 'a';
}

void f2(char* s){
*s = 'b';
}

int main(int argc,char** argv){
char a[] = "1234";
char* b = a;
printf("%s\n",a);
f1(b);
printf("%s\n",a);
f2(b);
printf("%s\n",a);
return 0;
}

The above prints:

The above doesn't compile:

fangorn:~/tmp 381> gcc -ansi -pedantic test.c
test.c:1: error: parse error before '&' token
test.c: In function `f1':
test.c:2: error: `s' undeclared (first use in this function)
test.c:2: error: (Each undeclared identifier is reported only once
test.c:2: error: for each function it appears in.)

Furthermore, calling printf without a correct declaration in scope
invokes undefined behaviour.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[James McIninch]

pembed2003 wrote:

Hi coders,
I have the following:

void f1(char* &s){
*s = 'a';
}

void f2(char* s){
*s = 'b';
}

int main(int argc,char** argv){
char a[] = "1234";
char* b = a;
printf("%s\n",a);
f1(b);
printf("%s\n",a);
f2(b);
printf("%s\n",a);
return 0;
}

The above prints:

1234
a234
b234

My question is:

1. How is char*& different from char* since they both do the same thing?
No. In C, char*& is a syntax error. There is no such syntax in C.

2. When do you use the first form and the second form?
You use char * all the time since the other form doesn't exist.


Thanks!

--
remove .spam from address to reply by e-mail.

[Chris Fogelklou]

"pembed2003" <pe********@yahoo.com> wrote in message
news:db**************************@posting.google.c om...

Hi coders,
I have the following:

void f1(char* &s){
*s = 'a';
}

void f2(char* s){
*s = 'b';
}

int main(int argc,char** argv){
char a[] = "1234";
char* b = a;
printf("%s\n",a);
f1(b);
printf("%s\n",a);
f2(b);
printf("%s\n",a);
return 0;
}

The above prints:

1234
a234
b234

My question is:

1. How is char*& different from char* since they both do the same thing?
2. When do you use the first form and the second form?

Thanks! void f1(char* &s){
As everyone said... this is a syntax error in C.
1. How is char*& different from char* since they both do the same thing?
However, in C++, you are passing a char * by reference... meaning, not only
could you have modified the character pointed to by 's' in the same way, but
the pointer 's' itself:

s = NULL; //This change would be undone by returning if s was not passed by
reference.

So, you must somehow be compiling in C++ rather than C.
2. When do you use the first form and the second form?

In C/C++, use the first form when you don't want to modify the value of the
variable passed in.

You would only use the second form in C++, and only when you want the
changes that you make to the variable to be returned to the calling program.

In C, you can only modify variables passed into a function through pointers:

void f1(char **ps){
*ps = NULL; //Kill s.
}