Qt with C?

[Mariane]

I don't know what the precise rules are, but in my limited experience
you can write some C in a C++ program provided you compile it as
C++ and not as C. Strings are a problem, though, don't mix C char
arrays and C++ strings.

But I've just written a bit of C in Qt :

FILE * logFile;
logFile = fopen(filename, "w");
etc,
where filename is of type QString and it worked fine.

Mariane

[high_flyer]

I don't know what the precise rules are, but in my limited experience
you can write some C in a C++ program provided you compile it as
C++ and not as C. Strings are a problem, though, don't mix C char
arrays and C++ strings.

When you compile C code as C++, then you have a C++ project.
But if you want to include *.c files or lets say import C compiled elements from a C library, then you are in trouble if you don't deal with the different signatures.

FILE * logFile;
logFile = fopen(filename, "w");
etc,
where filename is of type QString and it worked fine.

Are you sure about this?
fopen() doesnt know QString, so this is impossible, unless there is more to the code then you showed here.
Could you show the full relevant code?

[fullmetalcoder]

Are you sure about this?
fopen() doesnt know QString, so this is impossible, unless there is more to the code then you showed here.

I've never tried Qt3 but there may be an implicit conversion to char* :

QString::operator char* ()
{ ... }

QString::operator char* ()
{ ... }

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Anyway it's true that a C++ compiler handles lots of stuff in different way than a C one but code should be still compatible (maybe a few warnings if some type conversions are ambiguous, errors shouldn't come if your code isn't a damn spaghetti plate!!! )
Personnally I tried such a thing (I mean using C inside C++); I wrote a full file processing API using OOP and so on but the core used C (fopen, fgets, strcmp, ...) cuz, in my opinion, STL sucks and moreover, under mingw32, it makes your program bigger!)

[high_flyer]

Ok, I guess I am articulating my self poorly.
So, instead read the following, to understand what I meant in my previous posts:
http://en.wikipedia.org/wiki/Name_mangling
Pay attantion to the sections:
Name mangling in C++
Handling of C symbols when linking from C++

And this is not bad about mixed C and C++ code:
http://developers.sun.com/prodtech/c...es/mixing.html
And relevant to this thread, is the section: Accessing C++ Code From Within C Source

[high_flyer]

I've never tried Qt3 but there may be an implicit conversion to char* :

Not that I can see....
http://doc.trolltech.com/3.3/qstring.html
You have these methods for C like strings:
# const char * ascii () const
# const char * latin1 () const

[jacek]

Not that I can see....

How about this one: http://doc.trolltech.com/3.3/qstring...r-const-char-*?

[high_flyer]

I stand corrected.
I forgot to look in the "List of all member functions".
Sorry Mariane.

[jakamph]

Where I work, we have a lot of legacy C code that needs to be used in a QT project. As part of our coding standard, however, we have a rule that states that _any_ C header file must be framed by:

#ifdef __cplusplus
extern "C" {
#endif

#ifdef __cplusplus
extern "C" {
#endif

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and at the end of the header

#ifdef __cplusplus
}
#endif

#ifdef __cplusplus
}
#endif

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to ensure that we don't run in to problems with the different name mangling between C and C++. That wouldn't leave your original program untouched, I'm guessing, but it would avoid some of the potential problems of mixing the two.