What's the usage?

[ikl]

What's the usage of #ifdef and #endif in the code below?

#ifdef C_DEF
class C
{
public:
void Repair();
};

void C::Repair () {
....
}
#endif

Since I understand using like:

#ifdef C_DEF
class C
{
public:
void Repair();
};
#endif

void C::Repair () {
....
}


Thanks!

 

[Mike Wahler]

What's the usage of #ifdef and #endif in the code below?

#ifdef C_DEF

if the symbol 'C_DEF' is defined (with a #define directive),
then translate all the following code...

class C
{
public:
void Repair();
};

void C::Repair () {
...
}

.... until a

#endif

... directive is encountered.

Since I understand using like:

#ifdef C_DEF
class C
{
public:
void Repair();
};
#endif

This is the same as above, except it doesn't
include the definition of the member function
'Repair()'.

void C::Repair () {

A class 'C' must be visible at this point for
this to be valid.

...
}

Look up 'preprocessor directives' in your C++ book.

-Mike

 

[JaSeong Ju]

#ifdef and #endif are used for conditional compilation.
If C_DEF is defined, then compile in the class C and its
public member functions.

If C_DEF is not defined, then class C is
not included. Then of course you dont want to include
the
void C::Repair () {
....
}
member function, since its an error.

 

[Kevin Goodsell]

JaSeong Ju wrote:
<A top-posted message.>

Please stop top-posting. Read section 5 of the FAQ (which you should
have already read) for posting guidelines:

http://www.parashift.com/c++-faq-lite/

-Kevin