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Topic: C or C++? (Read 3617 times) |
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Eigenray
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Write a program that will print "C" if compiled as an (ANSI) C program, and "C++" if compiled as a C++ program.
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Eigenray
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Re: C or C++?
« Reply #1 on: Nov 5th, 2003, 6:35am » |
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Wow Eigenray, what a great problem! After working on it nonstop for 6 months, I finally came up with this:
$ cat foo.c
#include <stdio.h>
int main() {
int i=1//*
; //*/2;
printf("C%s\n",i?"++":"");
}
$ gcc -ansi -o C foo.c; ./C
C
$ g++ -o C++ foo.c; ./C++
C++
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towr
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Re: C or C++?
« Reply #2 on: Nov 5th, 2003, 7:30am » |
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hehe..
I think I have a solution somewhere in my mail-box, if you really want another one..
But personally I don't really like the comment-dependent solution.. Since that depends a lot on proper implementation of the compiler..
I wonder if there's another kind of solution..
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| « Last Edit: Nov 5th, 2003, 7:32am by towr » |
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Wikipedia, Google, Mathworld, Integer sequence DB
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Dudidu
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Re: C or C++?
« Reply #3 on: Nov 5th, 2003, 10:11am » |
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on Nov 5th, 2003, 6:35am, Eigenray wrote:| Wow Eigenray, what a great problem! After working on it nonstop for 6 months... |
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Eigenray you are absolutly right  , this is a very nice solution (and a problem).
As towr suggested this solution (without connection to how beautiful it is) might be a little bit problematic in real compilers since many of them do not follow exactly the standards of these languages. Nevertheless, Well done !!!
Quote:| I think I have a solution somewhere in my mail-box, if you really want another one.. |
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towr, if you have another solution, now it's a good time to show it  .
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towr
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Re: C or C++?
« Reply #4 on: Nov 5th, 2003, 11:35am » |
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I can't find it anymore, but it worked pretty much the same way..
here are two that should work, if the compilers work correctly (which they don't of course)
int main()
{
// ANSI/ISO c++ has to define __cplusplus
// unfortunately gcc seems to do it as well, while it shouldn't
#ifndef __cplusplus
printf("C\n");
#else
printf("C++\n");
#endif
}
int main()
{
// sizeof('c') is supposed to be sizeof(int)=4 in C,
// and 1 in C++, but guess what, it's so with gcc
if(sizeof('c') == 4)
printf("C\n");
else
printf("C++\n");
}
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Barukh
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Re: C or C++?
« Reply #5 on: Nov 6th, 2003, 2:32am » |
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In my opinion, both Eigenray's and towr's second solution are perfectly right. The point is - they give the correct solution if the compilers do what they should do (by the book).
Interestingly enough, the 3rd edition of Stroustrup's "C++ Programming Language" (1999) in section B.2.1 "Silent Differences" mentions 2 essential differences that actually coincide with here listed solutions.
Excellent problem!
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Margit
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gcc foo.c -o C
g++ foo.c -o C++
#include <stdio.h>
#include <string.h>
main(int argc, char **argv)
{
char *s;
if ( (s = strrchr(argv[0], '/')) != NULL )
{
s++;
} else {
s = argv[0];
}
printf("%s\n", s);
}
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Margit
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Or even :
gcc -ansi -DITSC foo2.c -o testit
./testit
C
g++ -DITSCPP foo2.c -o testit
./testit
C++
#include <stdio.h>
main()
{
#ifdef ITSC
printf("C\n");
#endif
#ifdef ITSCPP
printf("C++\n");
#endif
}
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Margit
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Hmm, this is interesting. What if we have to pass our prog to an unknown wrapper such as :
comp-c-or-cplus foo.c
So that we only know that we get a foo executable.
At any point in time, the wrapper will call either gcc or g++.
One of the definitive differences in dialect is the recognition of
operators like "and", "or" etc. in C++.
Wonder if we can exploit that.
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Rahul
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Rahul
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Re: C or C++?
« Reply #9 on: Nov 8th, 2003, 7:02pm » |
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Here's another one:
#include <stdio.h>
typedef struct {
} empty_t;
int main() {
char* s = sizeof(empty_t) ? "C++" : "C";
printf("%s\n", s);
}
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Margit
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Ah Rujoshi that's brilliant.
I even think that the behaviour cannot be changed
by any compile option.
The "definitive" answer.
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TenaliRaman
Uberpuzzler
I am no special. I am only passionately curious.
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Re: C or C++?
« Reply #11 on: Nov 20th, 2003, 10:00pm » |
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rujoshi,
all is fine with your solution except that it would generate a compile time error in C (not in C++ tho). In gcc however it will run with an exit code 2.
Nevertheless, its a brilliant solution !!! 
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Self discovery comes when a man measures himself against an obstacle - Antoine de Saint Exupery
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Rahul
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Rahul
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Re: C or C++?
« Reply #12 on: Nov 23rd, 2003, 12:57pm » |
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Hmm..yes, it doesn't work on a Sun..So here's another solution, which uses the
fact that C++ does name mangling and C does not.
// FindLang.c: compile using cc -o FLC.o FindLang.c
char* FindLang() {
return "C";
}
// FindLang.cpp: compile using c++ -o FLCPP.o FindLang.cpp
char* FindLang() {
return "C++";
}
// main.c: compile using cc/c++ -o main main.c FLC.o FLCPP.o
#include <stdio.h>
char* FindLang();
int main() {
printf("%s\n", FindLang());
}
This works on both Linux and Sun.
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| « Last Edit: Nov 23rd, 2003, 1:00pm by Rahul » |
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Rahul
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Rahul
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Re: C or C++?
« Reply #13 on: Nov 23rd, 2003, 1:20pm » |
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Another one I found at http://www.usenix.org/publications/login/1997-12/cplusplus.html:
/* corcpp.c */
#include <stdio.h>
char x;
int main() {
struct x { int xx[5]; };
char* s = (sizeof(x) == sizeof(char)) ? "C" : "C++";
printf ("%s\n", s);
}
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| « Last Edit: Nov 23rd, 2003, 1:20pm by Rahul » |
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TenaliRaman
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I am no special. I am only passionately curious.
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Re: C or C++?
« Reply #14 on: Nov 23rd, 2003, 9:50pm » |
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Rahul,
that's simply great solution at that site.
(i must say i never knew that trick!!)
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Self discovery comes when a man measures himself against an obstacle - Antoine de Saint Exupery
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