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easy array question

Hi. I want to pass an array through a function. how do i do this?

eg.

void SomeFunction(){
int Array[3];

Array[0] = 1;
Array[1] = 2;
Array[2] = 3;

SomeOtherRandomFunction(/*pass the array here*/);
}

void SomeOtherRandomFunction(/*what do i put here*/);
Hamish Dean, PhD

Jul 19 '05 #1
5 2333

"Hamish Dean" <h.****@xtra.co.nz> wrote in message
news:Y6**********************@news.xtra.co.nz...
Hi. I want to pass an array through a function. how do i do this?

eg.

void SomeFunction(){
int Array[3];

Array[0] = 1;
Array[1] = 2;
Array[2] = 3;

SomeOtherRandomFunction(/*pass the array here*/);
SomeOtherRandomFunction (Array);
}
void SomeOtherRandomFunction (int *Array) void SomeOtherRandomFunction(/*what do i put here*/);


HTH
Jul 19 '05 #2
void MyFunc( int *pInt, size_t size );
void SomeFunction(){
int Array[3];

Array[0] = 1;
Array[1] = 2;
Array[2] = 3;

// SomeOtherRandomFunction(/*pass the array here*/);
MyFunc( Array, sizeof(Array)/sizeof(Array[0]) );
}

void SomeOtherRandomFunction(/*what do i put here*/);

void MyFunc( int *pInt, size_t size )
{
for ( int i=0; i<size; ++i ) {
cout << *pInt++ << endl;
}
}

HTH
Rainer
Jul 19 '05 #3
Big Brian wrote:

Everybody seems to forget that C++ does support multidimensional
arrays in the language. Everybody imediately suggests using the STL
containers, but sometimes this isn't acceptable, and you need to use
the built in arrays.
Your code suggests that you fail to recognize some of the issues, and
that you may not understand exactly how arrays and functions work
together. It also demonstrates a problem that could be solved with
std::vector.

Consider this example....
#include <iostream>

void f( int array[5][3] )
Mmmmm... magic numbers. Even worse, one of them is completely
meaningless. This is equivalent to

void f( int array[][3] )

or

void f( int (*array)[3] )

Since the 5 does not provide useful information, your function does not
know how many rows this 2-d array contains.
{
for(int i = 0; i < 5; i++ )
Magic number... 5, eh? And what if there are not 5 rows? What if there
are 23? or 2? The only way to do this correctly would be to pass in the
number of rows as a separate argument.
{
for(int j = 0; j < 3; j++ )
Another magic number... but this time it could be replaced with

sizeof(*array) / sizeof((*array)[0])

Or something similar.
{
std::cout << "array[" << i << "," << j << "] ="
<< array[j][i]
Hmmm... what have we here? i goes from 0 to 4... but your second index
only goes from 0 to 2. You are going outside your array, causing
undefined behavior. This could have been caught if you had used
std::vector with the at() function.
<< std::endl;
}
}
}

int main(int argc , char * argv[])
{
int a[5][3] = {
{0,0,0},
{0,0,0},
{0,0,0},
{0,0,0},
{0,0,0} };

a[0][0] = 1;
a[2][4] = 4;
Again you've swapped indexes and gone outside the bounds of your array.

f(a);

return 0;
}


The final and most obvious problem with your code is that your function
is completely incapable of dealing with 2-d arrays that have a different
number of columns.

std::vector is usually a better solution, as it appears it would have
been in this case.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

Jul 19 '05 #4
> > Everybody seems to forget that C++ does support multidimensional
arrays in the language. Everybody imediately suggests using the STL
containers, but sometimes this isn't acceptable, and you need to use
the built in arrays.


Your code suggests that you fail to recognize some of the issues, and
that you may not understand exactly how arrays and functions work
together. It also demonstrates a problem that could be solved with
std::vector.

Consider this example....
#include <iostream>

void f( int array[5][3] )


Mmmmm... magic numbers. Even worse, one of them is completely
meaningless. This is equivalent to

void f( int array[][3] )

or

void f( int (*array)[3] )

Since the 5 does not provide useful information, your function does not
know how many rows this 2-d array contains.
{
for(int i = 0; i < 5; i++ )


Magic number... 5, eh? And what if there are not 5 rows? What if there
are 23? or 2? The only way to do this correctly would be to pass in the
number of rows as a separate argument.
{
for(int j = 0; j < 3; j++ )


Another magic number... but this time it could be replaced with

sizeof(*array) / sizeof((*array)[0])

Or something similar.
{
std::cout << "array[" << i << "," << j << "] ="
<< array[j][i]


Hmmm... what have we here? i goes from 0 to 4... but your second index
only goes from 0 to 2. You are going outside your array, causing
undefined behavior. This could have been caught if you had used
std::vector with the at() function.
<< std::endl;
}
}
}

int main(int argc , char * argv[])
{
int a[5][3] = {
{0,0,0},
{0,0,0},
{0,0,0},
{0,0,0},
{0,0,0} };

a[0][0] = 1;
a[2][4] = 4;


Again you've swapped indexes and gone outside the bounds of your array.

f(a);

return 0;
}


The final and most obvious problem with your code is that your function
is completely incapable of dealing with 2-d arrays that have a different
number of columns.

std::vector is usually a better solution, as it appears it would have
been in this case.


I understand there are issues with my example. I know there were
magic numbers, and other issues. I wasn't providing my code as bullet
proof. My point was that people automatically start saying "use
std::vector" when they don't understand the scope of the problem. The
original post asked about doing multidimensional arrays NOT
std::vector! Everybody only says use the STL. SOMETIMES YOU CAN'T USE
THE STL. That was my point!
Jul 19 '05 #5


Big Brian wrote:

Everybody seems to forget that C++ does support multidimensional
arrays in the language.
Sure. But the OP specifically requested a multidimensional array
with *dynamic sizing* capabilities.
Everybody imediately suggests using the STL
containers,
which is perfect for the OP's request.
but sometimes this isn't acceptable, and you need to use
the built in arrays.


True. But making this dynamic isn't that simple any more
compared to std::vector

--
Karl Heinz Buchegger
kb******@gascad.at
Jul 19 '05 #6

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