c++ type system

[Looney]

template
<
typename T,
unsigned int size

>

void DoStuff1(
T (& array)[size]
)
{}

template
<
typename T,
unsigned int size

>

void DoStuff2(
T (* array_p)[size]
)
{}

struct Pod
{
int data[10];
};

int main ()
{
Pod pod;
DoStuff1(pod.da ta); // does not compile why ??
DoStuff2(&pod.d ata); // this one is fine in comparison to the
above
}

I am just confused as how come a function parameter taking a reference
to an array leads to the data array decaying into a pointer (so type
info is lost and code does not compile), where as the function which
is taking a call parameter of a pointer to an array can compile and
keep on holding the type info.

[Looney]

Re: c++ type system

On Jul 10, 11:01 am, Looney <hardy_melbou.. .@hotmail.comwr ote:

template
<
        typename T,
        unsigned int size
>
void DoStuff1(
        T (& array)[size]
)
{}
>
template
<
        typename T,
        unsigned int size
>
void DoStuff2(
        T (* array_p)[size]
)
{}
>
struct Pod
{
        int data[10];
>
};
>
int main ()
{
    Pod pod;
    DoStuff1(pod.da ta); // does not compile why ??
    DoStuff2(&pod.d ata); // this one is fine in comparison to the
above
>
}
>
I am just confused as how come a function parameter taking a reference
to an array leads to the data array decaying into a pointer (so type
info is lost and code does not compile), where as the function which
is taking a call parameter of a pointer to an array can compile and
keep on holding the type info.

I do suspect it is due the implicit conversion applied to the array
object to make the reference to the array.
is n't it ?

[Looney]

Re: c++ type system

//---------------------------------------------------------------------------

#include <vcl.h>
#include <windows.h>
#pragma hdrstop

//---------------------------------------------------------------------------

template
<
typename T,
unsigned int size

>

void DoStuff1(
T (& array)[size]
)
{}

template
<
typename T,
unsigned int size

>

void DoStuff2(
T (* array_p)[size]
)
{}

struct Pod
{
int data[10];
};


#pragma argsused
WINAPI WinMain(HINSTAN CE hInstance, HINSTANCE hPrevInstance, LPSTR
lpCmdLine, int nCmdShow)
{
Pod pod;

int (& arrayref)[10] = pod.data;
DoStuff1(arrayr ef); // fine it compiles

DoStuff1(pod.da ta); // does not compile

DoStuff2(&pod.d ata);// fine it compiles

return 0;
}
//---------------------------------------------------------------------------

[Thomas J. Gritzan]

Re: c++ type system

Looney wrote:

//---------------------------------------------------------------------------
>
#include <vcl.h>
#include <windows.h>
#pragma hdrstop

[...]

I removed the Borland-specific stuff and shortened the example to:

//---------------------
template <typename T, unsigned int size>
void DoStuff1( T (& array)[size] )
{}

struct Pod
{
int data[10];
};

int main()
{
Pod pod;
DoStuff1(pod.da ta); // does not compile
return 0;
}
//---------------------

This doesn't compile with the Borland compiler, the error message is:

E2285 Could not find a match for 'DoStuff1<T,siz e>(int *)'

However, it compiles with GCC and Comeau, and using the array directly
without the struct it compiles with the Borland compiler, too:

int data[10];
DoStuff1(data); // compiles.

I guess it is a compiler error.

--
Thomas

[Looney]

Re: c++ type system

On Jul 10, 12:00 pm, "Thomas J. Gritzan" <phygon_antis.. .@gmx.de>
wrote:

Looney wrote:

//---------------------------------------------------------------------------

>

#include <vcl.h>
#include <windows.h>
#pragma hdrstop

>
[...]
>
I removed the Borland-specific stuff and shortened the example to:
>
//---------------------
template <typename T, unsigned int size>
void DoStuff1( T (& array)[size] )
{}
>
struct Pod
{
        int data[10];
>
};
>
int main()
{
        Pod pod;
        DoStuff1(pod.da ta); // does not compile
        return 0;}
>
//---------------------
>
This doesn't compile with the Borland compiler, the error message is:
>
E2285 Could not find a match for 'DoStuff1<T,siz e>(int *)'
>
However, it compiles with GCC and Comeau, and using the array directly
without the struct it compiles with the Borland compiler, too:
>
int data[10];
DoStuff1(data);  // compiles.
>
I guess it is a compiler error.
>
--
Thomas

Thanks for summing all of it up much more clearly & precisely.
It does seem bit odd and does indeed look like a compiler error.