OSDev.org

in vga.h I have :
void scroll ( int lines = 1 ) ;
in vga.c I have :
void scroll ( int lines )
{
//implementation
}
GCC gave me the error "Parse error before =" at the line containing the prototype in vga.h .
the only way to correct the error is to delete " = 1 " from prototype , but I want to use default values ,
I am sure that this way was successful in MS visual c++ & borland c++ .

default values for parameters are a feature present in C++, not C.

if you intended to use C++ then you shouldn't give your file a ".c" extention, but either ".C" or ".cpp" or ".cxx"

proxy

Those compilers might have different ways of 'guessing' if some code is C or C++ ... or simply use the C++ compiler for C code aswell ...

If renaming the source files is not an option for you, you may wish to use -x c++ flag in your GCC command line

this is the wrong way to do it...
do the following...
the default parameter MUST be given
at the implementation, NOT in the
prototype

Cemre, i am sorry but you are mistaken, while it is allowed to have it in the definition and not the prototype, it may be in either but not both. (see http://cplus.about.com/library/weekly/aa061102f.htm).

However, it is better convention to put it in the prototype, here is why.

typically when delivering a library, you deliver a binary source and headers. if the defaults are defined in the source but not the headers, how would the client ever know what the default value is or that there is any at all

proxy

Thanks you all , well , I'll continue using c and delete default parameters , but , I want to say that the default parameters
appear only one time ,not more at all . and this "one-time " should be the first time that the function appear which is usually ( but not always) the prototype . I am sure that this is true at least in C++ compilers under Windows that I mentioned before .
and "How to Program in C++" supports my opinion .

Thanks .

of course the C++ compilers supports it, like i said it is "a feature of C++ not C"

the problem is that your file is a .c file and any self respecting compiler will default to C mode for that, not C++.

proxy

For which I'm very happy that GCC can be forced to do C++, seeing as I would like my C code to compile with C++-esque name mangling...