C struct member default values in struct

[Rick C. Hodgin]

Is there a version of C or C++ extension which takes this:

struct SAbc
{
int a;
int b;
int c;
};

struct SAbc myAbcVar[] =
{
{ 1, 2, 3 },
{ 4, 5, 6 },
{ 7, 8, 9 }
};

And lets me change my structure to this:

struct SAbc
{
int a;
int b;
int c;
int d;
};

Without having to do this manually:

struct SAbc myAbcVar[] =
{
{ 1, 2, 3, -1 },
{ 4, 5, 6, -1 },
{ 7, 8, 9, -1 }
};

By allowing me instead to do something like this:

struct SAbc
{
int a;
int b;
int c;
int d = -1; // Default all unspecified values to -1
};

?

Does C++ or another C-like language have the ability to either
initialize all members in the struct definition, or to initialize
those members which are added on to the end later, as with C++'s
ability to initialize unspecified parameter values?

Best regards,
Rick C. Hodgin

[supe...@casperkitty.com]

On Wednesday, October 21, 2015 at 10:31:35 PM UTC-5, Rick C. Hodgin wrote:
> Is there a version of C or C++ extension which takes this...

It's possible to do a lot with the preprocessor, though in some cases you
may have to define a macro called something like "COMMA" to ensure that you
can embed commas in within a macro argument. I've done used macros to let
met me define default values for a structure at the same time as I defined
the structure itself (that was especially useful before named-field initial-
izers were added to the syntax). I'm not sure how best to set up the macros
for what you have in mind, but it would seem fairly straightforward.

[Frank Tetzel]

C++11 with initializer lists:

struct SAbc
{
int a;
int b;
int c;
int d = -1;

SAbc(int a, int b, int c) : a(a), b(b), c(c) {}
SAbc(int a, int b, int c, int d) : a(a), b(b), c(c), d(d) {}
};

SAbc myAbcVar[] { // = is optional
{0, 1, 2},
{0, 1, 2, 3}
};

Regards,
Frank

[Rick C. Hodgin]

Is the "=" optional in C? Or just C++11?

-----
The rest of my response is off-topic for the C group, but if you're
interested in seeing my CAlive implementation, go here:

https://groups.google.com/d/msg/rapid_development_compiler/FjprgbxfAiU/r_-lVoi0CgAJ

[Frank Tetzel]

> > C++11 with initializer lists:
> >
> > struct SAbc
> > {
> > int a;
> > int b;
> > int c;
> > int d = -1;
> >
> > SAbc(int a, int b, int c) : a(a), b(b), c(c) {}
> > SAbc(int a, int b, int c, int d) : a(a), b(b), c(c), d(d) {}
> > };
> >
> > SAbc myAbcVar[] { // = is optional
> > {0, 1, 2},
> > {0, 1, 2, 3}
> > };
>
> Is the "=" optional in C? Or just C++11?

Not in C as far as i know. It's new in C++11, see:

http://en.cppreference.com/w/cpp/language/list_initialization
http://en.cppreference.com/w/cpp/language/aggregate_initialization

[Rick C. Hodgin]

Because member default values are introduced, CAlive will also introduce
non-constructor instantiation of class objects when used as follows:

char invalid_data[] = "Invalid";

class CAbc
{
public:
CAbc(char* p) : m_p(p) { }
~CAbc() { }

private:
char* p = invalid_data;
}


void function(void)
{
// No constructor will be called, m_p initialized to "Invalid"
CAbc* abc = lnew CAbc;

// Constructor will be called, m_p initialized to "Rick"
CAbc* abc = lnew CAbc("Rick");

[Rick C. Hodgin]

On Wednesday, November 4, 2015 at 2:06:16 PM UTC-5, Rick C. Hodgin wrote:
> private:
> char* p = invalid_data;

Should be m_p, not p.