C program is standard C++ program?

[strutsng]

I want if "a C program is a standard C++ program, but not vice versa"
is a correct statement?

In a C++ program, we can use standard C libraries. However, we cannot
use C++ libraries inside C program.

Please advise. thanks!!

[John Carson]

"Michael Mair" <Mi**********@i nvalid.invalid> wrote in message
news:3r******** ****@individual .net

John Carson wrote:

"Martin Ambuhl" <ma*****@earthl ink.net> wrote in message
news:F8******** ********@newsre ad3.news.atl.ea rthlink.net

st******@gmail. com wrote:

I want if "a C program is a standard C++ program, but not vice
versa" is a correct statement?

It is a grossly erroneous statement. C and C++ are different
languages. There are countless C programs that are not C++
programs.
"C++ was developed from the C programming language and, with few
exceptions, retains C as a subset."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., p. 8.

This may have been the intent; however, Martin's statement still is
true as C++ semantics differ from C89 in many points.

The statement that "C++ ... with few exceptions retains C as a subset" is
not a statement of intent but a description of the relationship between the
two languages, albeit one that seems to be directed at C89. I quote again:

"With minor exceptions, C++ is a superset of C. Most differences stem from
C++'s greater emphasis on type checking. Well-written C programs tend to be
C++ programs as well."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., Appendix B,
Compatibility, p. 816.
C99 introduced enough additional non-trivial differences which cannot
be easily overcome.
That does indeed add to the incompatibility , though there are efforts
underway to bring the two languages closer together, particularly by adding
C99 stuff to C++.
The C standard does not make any claim w.r.t. C++
compatibility, even though there may be a rationale saying exactly
that. I do not own the C++ standard, so I cannot say anything from
this point of view.

Section 1.1/2 of the C++ standard:

"C++ is a general purpose programming language based on the C programming
language as described in ISO/IEC 9899:1990 Programming languages - C (1.2).
In addition to the facilities provided by C, C ++ provides additional data
types, classes, templates, exceptions, namespaces, inline functions,
operator overloading, function name overloading, references, free store
management operators, and additional library facilities."

Annex C (appropriately enough) of the C++ standard deals with the
relationship between C and C++, noting the areas of incompatibility .

--
John Carson

[Rolf Magnus]

John Carson wrote:

"Well-written C programs tend to be C++ programs as well."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., Appendix B,
Compatibility, p. 816.

I tend to disagree. In C, dynamic memory is usually allocated with malloc or
other functions that return a pointer to void. That pointer gets converted
implicitly into the target type in C, and a cast should be avoided in a
"well-written C program". However, in C++, it doesn't compile without a
cast. Dynamic memory is something that is used quite often, so I'd say that
most well-written C programs are not C++ programs and would need lots of
changes (in all places where dynamic memory is allocated).

[John Carson]

"Rolf Magnus" <ra******@t-online.de> wrote in message
news:dj******** *****@news.t-online.com

John Carson wrote:

"Well-written C programs tend to be C++ programs as well."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., Appendix B,
Compatibility, p. 816.

I tend to disagree. In C, dynamic memory is usually allocated with
malloc or other functions that return a pointer to void. That pointer
gets converted implicitly into the target type in C, and a cast
should be avoided in a "well-written C program". However, in C++, it
doesn't compile without a cast. Dynamic memory is something that is
used quite often, so I'd say that most well-written C programs are
not C++ programs and would need lots of changes (in all places where
dynamic memory is allocated).

Your point is covered in the preceding sentence: "Most differences stem from
C++'s greater emphasis on type checking." But I guess that this preceding
sentence somewhat gives the lie to the one that follows, so strictly
speaking you are probably right that "most well-written C programs are not
C++ programs".

I am more sceptical about your claim that they would need "lots of changes".
Well written C programs will hide most of the malloc calls inside
initialization functions --- manual equivalents of constructors --- and the
number of these shouldn't be very large.

--
John Carson

[Michael Mair]

John Carson wrote:

"Michael Mair" <Mi**********@i nvalid.invalid> wrote in message
news:3r******** ****@individual .net

John Carson wrote:

"Martin Ambuhl" <ma*****@earthl ink.net> wrote in message
news:F8******** ********@newsre ad3.news.atl.ea rthlink.net

st******@gmail. com wrote:

> I want if "a C program is a standard C++ program, but not vice
> versa" is a correct statement?

It is a grossly erroneous statement. C and C++ are different
languages. There are countless C programs that are not C++
programs.

"C++ was developed from the C programming language and, with few
exceptions, retains C as a subset."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., p. 8.

This may have been the intent; however, Martin's statement still is
true as C++ semantics differ from C89 in many points.

The statement that "C++ ... with few exceptions retains C as a subset" is
not a statement of intent but a description of the relationship between the
two languages, albeit one that seems to be directed at C89. I quote again:

"With minor exceptions, C++ is a superset of C. Most differences stem from
C++'s greater emphasis on type checking. Well-written C programs tend to be
C++ programs as well."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., Appendix B,
Compatibility, p. 816.

Hmmm, my C code tends to look quite different from my C++ code.
Things I find quite acceptable in C are not acceptable in C++
where better solutions to address certain problems exist.

Apart from the different semantics of void* and ambiguities w.r.t.
overloaded functions, there are better ways to perform explicit
type conversions in C++ than the good old C-style cast.

C99 introduced enough additional non-trivial differences which cannot
be easily overcome.

That does indeed add to the incompatibility , though there are efforts
underway to bring the two languages closer together, particularly by adding
C99 stuff to C++.

Yes, AFAIR there were a couple of good articles by B.Stroustrup in CUJ
about the areas where this is easily possible and where in his opinion,
either C++ or C should change semantics. They may still be available
online.

The C standard does not make any claim w.r.t. C++
compatibility, even though there may be a rationale saying exactly
that. I do not own the C++ standard, so I cannot say anything from
this point of view.

Section 1.1/2 of the C++ standard:

"C++ is a general purpose programming language based on the C programming
language as described in ISO/IEC 9899:1990 Programming languages - C (1.2).
In addition to the facilities provided by C, C ++ provides additional data
types, classes, templates, exceptions, namespaces, inline functions,
operator overloading, function name overloading, references, free store
management operators, and additional library facilities."

Annex C (appropriately enough) of the C++ standard deals with the
relationship between C and C++, noting the areas of incompatibility .

Thank you for the information :-)
Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.

[Branimir Maksimovic]

<st******@gmail .com> wrote in message
news:11******** **************@ g14g2000cwa.goo glegroups.com.. .

I want if "a C program is a standard C++ program, but not vice versa"
is a correct statement?

In a C++ program, we can use standard C libraries.
No we can't

extern "C"{
void strcpy(char* restrict , const char* restrict);
}

Standard C++ compiler should spit error.
Only non standard C++ compiler with appropriate
extensions can use standard C libraries.

However, we cannot use C++ libraries inside C program.

Yes we can
extern "C" void myfunc(int){ MyClass o; } // defines C function
// that can be called from C

Greetings, Bane.

[Branimir Maksimovic]

"Branimir Maksimovic" <bm***@eunet.yu > wrote in message
news:dj******** **@news.eunet.y u...

<st******@gmail .com> wrote in message
news:11******** **************@ g14g2000cwa.goo glegroups.com.. .

I want if "a C program is a standard C++ program, but not vice versa"
is a correct statement?

In a C++ program, we can use standard C libraries.
No we can't

extern "C"{
void strcpy(char* restrict , const char* restrict);

void strcpy(char* restrict to, const char* restrict from); }

Standard C++ compiler should spit error. Worse, if there are no variables it can interpret "restrict" as parameter
name
instead of type qualifier :)
Only non standard C++ compiler with appropriate
extensions can use standard C libraries.

[Keith Thompson]

Michael Mair <Mi**********@i nvalid.invalid> writes:

John Carson wrote:

[...]

The statement that "C++ ... with few exceptions retains C as a
subset" is not a statement of intent but a description of the
relationship between the two languages, albeit one that seems to be
directed at C89. I quote again: "With minor exceptions, C++ is a
superset of C. Most differences stem from C++'s greater emphasis on
type checking. Well-written C programs tend to be C++ programs as
well."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., Appendix B,
Compatibility, p. 816.

Hmmm, my C code tends to look quite different from my C++ code.
Things I find quite acceptable in C are not acceptable in C++
where better solutions to address certain problems exist.

Apart from the different semantics of void* and ambiguities w.r.t.
overloaded functions, there are better ways to perform explicit
type conversions in C++ than the good old C-style cast.

Stroustrup's statement is that well-written C programs tend to be C++
programs, not that well-written C programs tend to be *well-written*
C++ programs.

The former statement is basically true apart from the issue of casting
the result of malloc(). The latter is not.

--
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.

[Keith Thompson]

"Branimir Maksimovic" <bm***@eunet.yu > writes:

<st******@gmail .com> wrote in message
news:11******** **************@ g14g2000cwa.goo glegroups.com.. .

I want if "a C program is a standard C++ program, but not vice versa"
is a correct statement?

In a C++ program, we can use standard C libraries.

No we can't

extern "C"{
void strcpy(char* restrict , const char* restrict);
}

Standard C++ compiler should spit error.
Only non standard C++ compiler with appropriate
extensions can use standard C libraries.

Presumably a header intended to be used by both C and C++ compilers
could have

#ifdef __cplusplus
#define restrict
#endif

--
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.

[Martin Ambuhl]

John Carson wrote:

"With minor exceptions, C++ is a superset of C. Most differences stem from
C++'s greater emphasis on type checking. Well-written C programs tend to be
C++ programs as well."
Bjarne Stroustrup, The C++ Programming Language, 3rd ed., Appendix B,
Compatibility, p. 816.

This is an example of why one should *not* cite Stroustrup as an
authority on this issue. He is obviously an authority on C++, but the
fact is that well-written C programs tend to be uncompilable as C++.
Best C practice is often illegal in C++. Remember that BS has a horse
in this race.

[Branimir Maksimovic]

"Keith Thompson" <ks***@mib.or g> wrote in message
news:ln******** ****@nuthaus.mi b.org...

"Branimir Maksimovic" <bm***@eunet.yu > writes:

<st******@gmail .com> wrote in message
news:11******** **************@ g14g2000cwa.goo glegroups.com.. .

I want if "a C program is a standard C++ program, but not vice versa"
is a correct statement?

In a C++ program, we can use standard C libraries.

No we can't

extern "C"{
void strcpy(char* restrict , const char* restrict);
}

Standard C++ compiler should spit error.
Only non standard C++ compiler with appropriate
extensions can use standard C libraries.

Presumably a header intended to be used by both C and C++ compilers
could have

#ifdef __cplusplus
#define restrict
#endif

This can be dangerous. restrict type qualifier has specific meaning to C
compiler,
and does not mean anything to C++ compiler, so C++ calling C function with
such parameter can lead to undefined behavior,
therefore it is better to live that as it is.

Greetings, Bane.