Set boolean array elements to false using STL algorithm?

[Jason Heyes]

What STL algorithm do I use to set all bool elements of an array to false in
just one line of code? Thanks!

[Peter_Julian]

"Jason Heyes" <ja********@optusnet.com.au> wrote in message
news:43***********************@news.optusnet.com.a u...
| What STL algorithm do I use to set all bool elements of an array to
false in
| just one line of code? Thanks!
|
|

What makes you believe that you need an algorithm to do that?

#include <iostream>
#include <ostream>
#include <vector>

int main()
{
const sz(10);
bool ba[sz] = {false};

std::cout << "bool array with size = " << sz << "\n";
for(int i = 0; i < sz; ++i)
{
std::cout << "ba[" << i << "] = " << ba[i];
std::cout << std::endl;
}

std::vector<bool> vb(10, false);

std::cout << "bool vector with size = " << sz << "\n";
for(int j = 0; j < sz; ++j)
{
std::cout << "ba[" << j << "] = " << ba[j];
std::cout << std::endl;
}

return 0;
}

/*
bool array with size = 10
ba[0] = 0
ba[1] = 0
ba[2] = 0
ba[3] = 0
ba[4] = 0
ba[5] = 0
ba[6] = 0
ba[7] = 0
ba[8] = 0
ba[9] = 0
bool vector with size = 10
ba[0] = 0
ba[1] = 0
ba[2] = 0
ba[3] = 0
ba[4] = 0
ba[5] = 0
ba[6] = 0
ba[7] = 0
ba[8] = 0
ba[9] = 0
*/

[Jason Heyes]

>

What makes you believe that you need an algorithm to do that?

Here is why.

class Array {
bool arr[10];
public:
Array() { /* initialise arr */ }
};

What do I put in place of the comment if I want to initialise arr in just a
single line of code?

[Greg]

Jason Heyes wrote:

What makes you believe that you need an algorithm to do that?

Here is why.

class Array {
bool arr[10];
public:
Array() { /* initialise arr */ }
};

What do I put in place of the comment if I want to initialise arr in just a
single line of code?

#include <algorithm>

class Array
{
bool arr[10];
public:
Array()
{
std::fill_n( arr, sizeof(arr)/sizeof(arr[0]), 0);
}
};

Greg

[Maxim Yegorushkin]

Jason Heyes wrote:

What makes you believe that you need an algorithm to do that?

Here is why.

class Array {
bool arr[10];
public:
Array() { /* initialise arr */ }
};

You can default initialize member arrays using the following syntax:

Array() : arr() { ... }

[Jason Heyes]

>

You can default initialize member arrays using the following syntax:

Array() : arr() { ... }

I tried this in a small program and it did not initialise the array.

#include <iostream>
#include <algorithm>
#include <iterator>

class Array
{
int arr[10];
public:
Array() : arr()
{
std::copy(arr, arr + 10, std::ostream_iterator<int>(std::cout,
"\n"));
}
};

int main()
{
Array array;
return 0;
}

The output of the program was this.

-858993460
-858993460
-858993460
-858993460
-858993460
-858993460
-858993460
-858993460
-858993460
-858993460

Are you sure you can initialise member arrays in the way you have described?

Jason.

[romain.gaucher]

you cannot !
there is no std default contruction of integers, boolean etc.
"arr()" doesn't mean anything here and you have to do a loop

[Clark S. Cox III]

On 2006-01-02 08:47:31 -0500, "ro************@gmail.com"
<ro************@gmail.com> said:

you cannot !
there is no std default contruction of integers, boolean etc.
"arr()" doesn't mean anything here and you have to do a loop

Are you claiming that the following program can print anything other
than the number zero?

#include <iostream>
using namespace std;

struct Foo
{
int i;
Foo() : i() { cout << i << endl; }
};

int main()
{
Foo foo;
}

--
Clark S. Cox, III
cl*******@gmail.com

[Maxim Yegorushkin]

Jason Heyes wrote:

You can default initialize member arrays using the following syntax:

Array() : arr() { ... }

I tried this in a small program and it did not initialise the array.

It does, refer to the standard §8.5/5.

You are probably using an utterly outdated compiler, such as VC6.
Upgrade to recent one.

[Jason Heyes]

>

you cannot !
there is no std default contruction of integers, boolean etc.
"arr()" doesn't mean anything here and you have to do a loop

Are you claiming that the following program can print anything other than
the number zero?

#include <iostream>
using namespace std;

struct Foo
{
int i;
Foo() : i() { cout << i << endl; }
};

int main()
{
Foo foo;
}

There is no default initialisation of integers, boolean, etc, in arrays.

[red floyd]

Jason Heyes wrote:

you cannot !
there is no std default contruction of integers, boolean etc.
"arr()" doesn't mean anything here and you have to do a loop

Are you claiming that the following program can print anything other than
the number zero?

#include <iostream>
using namespace std;

struct Foo
{
int i;
Foo() : i() { cout << i << endl; }
};

int main()
{
Foo foo;
}

There is no default initialisation of integers, boolean, etc, in arrays.

The above code should print 0. If you look he uses the default
constructor for i.

int x = int();

*Will* initialize x to 0. Unfortunately, I don't have a copy of the
Standard in front of me, so I can't quote chapter and verse.

[Maxim Yegorushkin]

ro************@gmail.com wrote:

you cannot !
there is no std default contruction of integers, boolean etc.
"arr()" doesn't mean anything here and you have to do a loop

You are mistaken. Refer to §8.5.