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There is an error in my program. The error message is

e:\test\test\main.cpp(9): error C2664: 'fun' : cannot convert parameter 1
from 'int [2][3]' to 'int ** '

If I change the argument "int** a" to "int a[2][3], it will be OK. But, I
don't want to change the definition.
How can I pass the matrix to the function?

//-------------------------------------------------------------
void fun(int **a,const int row,const int col);

void main()
{

int a[2][3];
fun(a,2,3);
}

void fun(int **a,const int row,const int col)
{
for(int i=0;i<row;++i)
for(int j=0;j<col;++j)
a[i][j]=i*10+j;
}

Try making your int **a into an int (*a)[3] this way you actualy tell the
computer you want a pointer to an array that has a 3 ints in it. If you had
an **int this is just double indirection, and with(*)[] you have a pointer
to an array.

HTH

--
Frane Roje

Have a nice day

Remove (d*el*ete) from email to reply

Try making your int **a into an int (*a)[3] this way you actualy tell the
computer you want a pointer to an array that has a 3 ints in it. If you had
an **int this is just double indirection, and with(*)[] you have a pointer
to an array.

HTH

--
Frane Roje

Have a nice day

Remove (d*el*ete) from email to reply

> e:\test\test\main.cpp(9): error C2664: 'fun' : cannot convert parameter 1
> from 'int [2][3]' to 'int ** '
>
> If I change the argument "int** a" to "int a[2][3], it will be OK. But, I
> don't want to change the definition.
> How can I pass the matrix to the function?

Usually int [2][3] is implemented as a flat array while int** is a pointer
to a pointer which is something completely different.
So it is not possible to transfer int a[2][3] as int**

Niels Dybdahl

In article <ca1f5m$292u$>, Wei-Chao Hsu wrote:
> There is an error in my program. The error message is
>
> e:\test\test\main.cpp(9): error C2664: 'fun' : cannot convert parameter 1
> from 'int [2][3]' to 'int ** '

That can't be done. int a[2][3] is not stored as an a**. It's stored
as an array, whith each element as an int[3]. You could define fun() like
this:

void fun(int a[][3], const int row)
{
for (...) for (...) a[i][j]=...;
}

Note all but the first index needs to be known at compile time. You
could also define fun() like this:

void fun(int *a, const int row, const int col)
{
for (int i=0;i<row;++i) for (int j=0;j<col;++j)
a[i*col + j] = i*10+j;
}

but then fun must be called as this:

fun(reinterpret_cast<int*>(a), 2, 3)

There is more than one way to do things, but: C++ has something called
classes. To implement a matrix is better done using this feature than
plain arrays.

> If I change the argument "int** a" to "int a[2][3], it will be OK. But, I
> don't want to change the definition.
> How can I pass the matrix to the function?

You would need to change the definition of fun.

> //-------------------------------------------------------------
> void fun(int **a,const int row,const int col);
>
> void main()

int main()

> {
>
> int a[2][3];
> fun(a,2,3);
> }
>
> void fun(int **a,const int row,const int col)
> {
> for(int i=0;i<row;++i)
> for(int j=0;j<col;++j)
> a[i][j]=i*10+j;
> }


--
Robert Bauck Hamar

I just learn C++ recently and need to rewrite some programs from FORTRAN to
C++. In the programs, the sizes of matrices are always determined at
runtime. Passing a multiple dimensional array to a function is very easy to
FORTRAN, but it seems to be a problem to C/C++.
> There is an error in my program. The error message is
>
> e:\test\test\main.cpp(9): error C2664: 'fun' : cannot convert parameter 1
> from 'int [2][3]' to 'int ** '
>
> If I change the argument "int** a" to "int a[2][3], it will be OK. But, I
> don't want to change the definition.
> How can I pass the matrix to the function?
>
> //-------------------------------------------------------------
> void fun(int **a,const int row,const int col);
>
> void main()
> {
>
> int a[2][3];
> fun(a,2,3);
> }
>
> void fun(int **a,const int row,const int col)
> {
> for(int i=0;i<row;++i)
> for(int j=0;j<col;++j)
> a[i][j]=i*10+j;
> }
>
>

I think I find the solution, but I don't know whether the method for
deallocating is correct. Any idea?
Another question- If I don't delete the memory, will it deallocate the
memory automatically after the function is ended?

//--------------------------------------------------------
void fun(int *a,const int row,const int col);

void main()
{
const row=9;
const col=8;
int a[row][col];
int *pa=&a[0][0];

fun(pa,row,col);
}

void fun(int *pa,const int row,const int col)
{
int **a=new int*[row];
a[0]=pa;
for(int i=1;i<row;++i)
a[i]=&a[i-1][col];

for(int i=0;i<row;++i)
for(int j=0;j<col;++j)
a[i][j]=i*10+j;

delete [] a;
}

Wei-Chao Hsu wrote:
>
> I just learn C++ recently and need to rewrite some programs from FORTRAN to
> C++. In the programs, the sizes of matrices are always determined at
> runtime. Passing a multiple dimensional array to a function is very easy to
> FORTRAN, but it seems to be a problem to C/C++.

Arrays in general are a pain in the ass in C++. Especially if they
need to be dynamically sized. A std::vector is much easier to
deal with since it is a first class object. An example
of using a std::vector has already been shown I think.

--
Karl Heinz Buchegger

<SNIP>

> void main()
> {
>
> int a[2][3];
> fun(a,2,3);
> }

This does not answer your question, but 'main' should be declared 'int', not 'void'.

following code works.

> void main()
> {
>
> int a[2][3];
use "int** a = NULL;"
> fun(a,2,3);
> }
>

void fun(int** & p_Array, const int row,const int col)
{
if (p_Array) delete p_Array;
p_Array = new int* [row];
for (int i = 0; i < row; i++)
p_Array[i] = new int[col];

for(int i=0;i<row;++i)
{for(int j=0;j<col;++j)
{ p_Array[i][j]=i*10+j; }
}
}




-- xiaobin