extern "c" usage?!!

[Medvedev]

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
..
..
..
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

[Mike Wahler]

"Medvedev" <3D********@gmail.comwrote in message
news:7f**********************************@t54g2000 hsg.googlegroups.com...

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
.
.
.
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

extern "C"
{

}

... causes any functions inside the braces to have
"C linkage", so that they can be called from C
functions. There's nothing about 'constant' here.

The #ifdef will cause 'extern C' to be applied only
if translating C++ code.

-Mike

[Medvedev]

On Jul 6, 2:12 pm, "Mike Wahler" <[e-mail]:

"Medvedev" <[e-mail] in message

news:7f**********************************@t54g2000 hsg.googlegroups.com...

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
.
.
.
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

extern "C"
{

}

.. causes any functions inside the braces to have
"C linkage", so that they can be called from C
functions. There's nothing about 'constant' here.

sorry , but what differ C++ functions from C ones

[Jim Langston]

"Medvedev" <3D********@gmail.comwrote in message
news:ce**********************************@e53g2000 hsa.googlegroups.com...

On Jul 6, 2:12 pm, "Mike Wahler" <[e-mail]:

>"Medvedev" <[e-mail] in message

news:7f**********************************@t54g200 0hsg.googlegroups.com...

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
.
.
.
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

extern "C"
{

}

.. causes any functions inside the braces to have
"C linkage", so that they can be called from C
functions. There's nothing about 'constant' here.

sorry , but what differ C++ functions from C ones

C++ functions have overloading. C functions do not. This means there is
only one definition for a C function, there can be more than one for a C++
function. Compilers typcially handle this by "mangling". This will change
the name of the C++ function in the object file so the linker can
differentiate between calling parameters.

stating:
extern "C" {
tells the compiler not to mangle the function names, there will only be one
declaration for each function, so then when it is linked it has C linkage,
the function name would be the same as if it was a C function, and C
programs/objects can call the function as they can now link to them.

[Mike Wahler]

"Medvedev" <3D********@gmail.comwrote in message
news:ce**********************************@e53g2000 hsa.googlegroups.com...

On Jul 6, 2:12 pm, "Mike Wahler" <[e-mail]:

>"Medvedev" <[e-mail] in message

news:7f**********************************@t54g200 0hsg.googlegroups.com...

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
.
.
.
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

extern "C"
{

}

.. causes any functions inside the braces to have
"C linkage", so that they can be called from C
functions. There's nothing about 'constant' here.

sorry , but what differ C++ functions from C ones

Think about overloading. You can have more than a
single function with the same name (the number and/or
types of arguments would differ.

int foo(void);
int foo(int);
int foo(int,int);

C++ needs to distinguish these functions from one another.
There's no specific method required by the standard, but
typically the compiler will 'mangle' the names (change and/or
add characters) so that they become unique.

"extern C" prevents this 'mangling', so that the function
can be linked with C (using its 'real' name).

Anyway, I should have already cited this link from the C++ FAQ:
http://www.parashift.com/c++-faq-lit...c-and-cpp.html

This explains it better than I.

-Mike

[James Kanze]

On Jul 7, 12:18 am, Medvedev <[e-mail]:

On Jul 6, 2:12 pm, "Mike Wahler" <[e-mail]:

"Medvedev" <[e-mail] in message

news:7f**********************************@t54g2000 hsg.googlegroups.com....

What's that preprocessor do
#ifdef __cplusplus
extern "C" {
#endif
.
.
.
#ifdef __cplusplus
}
#endif

and how you say extern "C" , i mean how u extern constant!!

extern "C"
{
}

.. causes any functions inside the braces to have
"C linkage", so that they can be called from C
functions. There's nothing about 'constant' here.

sorry , but what differ C++ functions from C ones

Whatever the implementation wants. There's no fundamental
reason for two different languages to use the same calling
conventions. One typical difference might be that in C++, the
call stack is cleaned up in the called function (since it
involves calling destructors, etc.), where as in C, it is
cleaned up in the callee (since historically, C didn't have
prototypes, and allowed calling a function with extra arguments,
which were ignored). Also, C++ has overloading, which means
that some sort of information concerning the type and number of
arguments must be maintained in the object file. And because C
allowed extra arguments, a C compiler will not want to do this.

--
James Kanze (GABI Software) email:ja*********@gmail.com
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