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Seung-Uk Oh
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 Posted: Fri Jun 27, 2003 12:31 pm Post subject: [Question] parameter passing between C and C++ |
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Hi, everyone!
We are developing an application using both C and C++.
We have defined a structure in a C program as follows:
typedef struct node {
struct node *next;
int value;
}List;
And we construct a linked list using the above structure.
Then we pass the linked list to a function which is defined
in a C++ program enclosed with "extern "C" { }".
e.g.)
IN C-program
typedef struct node {
struct node *next;
int value;
}List;
int main(){
List *l;
/* l is initialized */
function_in_cpp(l);
}
IN C++-program
extern "C" {
typedef struct node {
struct node *next;
int value;
}List;
function_in_cpp(List *l)
{
....
}
}
When the length of a linked list is 1, the function call to
a function in a C++ is successful. However, when we call the function
in C++ program with the linked list whose length is 2, the actual
parameter in the C++ program is NULL. So, we can't pass the desired
value to a function in the C++ program.
Is there any difference between C and C++ in representing a "struct"
type variable? If any, the difference results in the consequence?
Please anybody help me.
Thanks in advance
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Victor Bazarov
Guest
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| Posted: Fri Jun 27, 2003 1:44 pm Post subject: Re: [Question] parameter passing between C and C++ |
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"Seung-Uk Oh" <suoh (AT) macroimpact (DOT) com> wrote...
| Quote: | We are developing an application using both C and C++.
We have defined a structure in a C program as follows:
typedef struct node {
struct node *next;
int value;
}List;
And we construct a linked list using the above structure.
Then we pass the linked list to a function which is defined
in a C++ program enclosed with "extern "C" { }".
|
That may not work. C object model differs from C++ object
model. Objects created in C may not be recognised in C++.
| Quote: |
e.g.)
IN C-program
typedef struct node {
struct node *next;
int value;
}List;
int main(){
List *l;
/* l is initialized */
function_in_cpp(l);
}
IN C++-program
extern "C" {
typedef struct node {
struct node *next;
int value;
}List;
function_in_cpp(List *l)
{
...
}
}
When the length of a linked list is 1, the function call to
a function in a C++ is successful. However, when we call the function
in C++ program with the linked list whose length is 2, the actual
parameter in the C++ program is NULL. So, we can't pass the desired
value to a function in the C++ program.
|
To verify that claim we would need a complete program. There is
no guarantee that at the moment of the call to the C++ function
with a list of length 2 you haven't make a mistake and the list
isn't really garbage.
| Quote: |
Is there any difference between C and C++ in representing a "struct"
type variable? If any, the difference results in the consequence?
|
There probably is.
Objects created in the part of the program written in a certain
language should be processed in the part of the program written
in the same language, unless there is a way to convert them (like
XML document, for example, but that's very similar to basic I/O)
or they are passed by value interpreted the same way in both
languages (e.g. 'int' or 'char' or pointers thereof).
Victor
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Alexander Terekhov
Guest
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| Posted: Fri Jun 27, 2003 2:14 pm Post subject: Re: [Question] parameter passing between C and C++ |
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Victor Bazarov wrote:
| Quote: |
"Seung-Uk Oh" <suoh (AT) macroimpact (DOT) com> wrote...
We are developing an application using both C and C++.
We have defined a structure in a C program as follows:
typedef struct node {
struct node *next;
int value;
}List;
And we construct a linked list using the above structure.
Then we pass the linked list to a function which is defined
in a C++ program enclosed with "extern "C" { }".
That may not work. C object model differs from C++ object
model. Objects created in C may not be recognised in C++.
|
Friday.
regards,
alexander.
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Jerry Coffin
Guest
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| Posted: Sat Jun 28, 2003 1:59 am Post subject: Re: [Question] parameter passing between C and C++ |
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In article <vfoii2cp9ebd7e (AT) corp (DOT) supernews.com>, [email]v.Abazarov (AT) attAbi (DOT) com[/email]
says...
| Quote: | "Seung-Uk Oh" <suoh (AT) macroimpact (DOT) com> wrote...
We are developing an application using both C and C++.
We have defined a structure in a C program as follows:
typedef struct node {
struct node *next;
int value;
}List;
And we construct a linked list using the above structure.
Then we pass the linked list to a function which is defined
in a C++ program enclosed with "extern "C" { }".
That may not work. C object model differs from C++ object
model. Objects created in C may not be recognised in C++.
|
Hmm...while it's difficult for the C++ standard to require it directly,
the struct above is pretty clearly a POD struct, and it does its best to
ensure that POD structs will be layout compatible with C.
[ ... ]
| Quote: | Is there any difference between C and C++ in representing a "struct"
type variable? If any, the difference results in the consequence?
There probably is.
|
There shouldn't normally be. As I said above, it's virtually impossible
for the C++ standard to come out and directly say it has to be
compatible with C, it comes about as close as the committee figured they
could to doing exactly that.
| Quote: | Objects created in the part of the program written in a certain
language should be processed in the part of the program written
in the same language, unless there is a way to convert them (like
XML document, for example, but that's very similar to basic I/O)
or they are passed by value interpreted the same way in both
languages (e.g. 'int' or 'char' or pointers thereof).
|
This can certainly simplify things considerably. Perhaps more to the
point, there's not often much need to mix C and C++ for the simple
reason that at least if you have well-written source code for the C
part, chances are that converting it to compile as C++ will be fairly
trivial. Nonetheless, you don't always have well-written source code to
work with, and in that case, mixing C and C++ is perfectly reasonable
and passing structs back and forth between the two normally works quite
well.
--
Later,
Jerry.
The universe is a figment of its own imagination.
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