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Hi,

Can someone show me how to set any integer (or float) in an std::vector
as zero in a way other than using a for loop? Can we apply memset() or
ZeroMemory() to the vector? Thanks for your help.

JD

JDT wrote:
> Can someone show me how to set any integer (or float) in an
> std::vector as zero in a way other than using a for loop? Can we
> apply memset() or ZeroMemory() to the vector?

No.

vector<float> myvector;
... // fill myvector with something

vector<float>(myvector.size(), 0f).swap(myvector);

V
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* JDT:
>
> Can someone show me how to set any integer (or float) in an std::vector
> as zero in a way other than using a for loop?

Note that any way you do it, there will be a loop, at some level of the
implementation.

An easy but perhaps not the most efficient way for a vector v of type V is

V( v.size() ).swap( v );

Or you can do e.g.

std::fill( v.begin(), v.end(), 0 );




> Can we apply memset() or
> ZeroMemory() to the vector?

std::memset can be applied to a vector of POD element type, but it's not
recommended, especially not for one who is in doubt about its usage.

ZeroMemory is not a standard C++ function.

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"JDT" <> wrote in message
news:ZKfsh.68668$. net...
> Hi,
>
> Can someone show me how to set any integer (or float) in an std::vector as
> zero in a way other than using a for loop? Can we apply memset() or
> ZeroMemory() to the vector? Thanks for your help.
>
> JD

You *could* use memset, but personally I don't like it. The reason being it
can break classes.

Say, for instance you have a std::vector of a simple POD class such as:

class MyClass
{
public:
int MyInt;
float MyFloat;
char MyChar;
};

std::vector<MyClass> MyVector;

So you go ahead and use memset something like (this may be off):

memset( &MyVector[0], 0, sizeof MyClass * MyVector.count() );

Okay, it works for now. But maybe later you change MyClass to also include
something that's not POD.

class MyClass
{
public:
int MyInt;
float MyFloat;
char MyChar;
std::string MyString;
};

the memset will still set the variables to 0, but now you just broke
MyString. MyString has a constructor that sets all kinds of things such as
pointers that aren't necessarily 0.

Consider alternatives.

JDT <> wrote:

> Can someone show me how to set any integer (or float) in an std::vector
> as zero in a way other than using a for loop? Can we apply memset() or
> ZeroMemory() to the vector? Thanks for your help.

You could just assign 0 to the element you want to set. If you meant
"every" instead of "any". There are several ways:

a) The vector/swap trick that Victor & Alf showed.
b) The std::fill algorithm that Alf showed.

You could also:

unsigned s = vec.size();
vec.clear();
vec.resize( s );

Victor Bazarov wrote:
> JDT wrote:
>> Can someone show me how to set any integer (or float) in an
>> std::vector as zero in a way other than using a for loop? Can we
>> apply memset() or ZeroMemory() to the vector?
>
> No.
>
Hmmm.... the question says how to initialize the vector. So would not
this satisfy the question:

std::vector<int> v;
v.resize(100);

Thus creating 100 elements that are all default initialized, or 0
initialized in the case of ints.

--
Ivan
http://www.0x4849.net

"JDT" <> wrote in message
news:ZKfsh.68668$. net
> Hi,
>
> Can someone show me how to set any integer (or float) in an
> std::vector as zero in a way other than using a for loop? Can we
> apply memset() or ZeroMemory() to the vector? Thanks for your help.
>
> JD


For a vector with 100 zeros:

vector<int> v(100,0);


--
John Carson

"Ivan Novick" <> wrote in message
news:Quish.36248$ et
> Victor Bazarov wrote:
>> JDT wrote:
>>> Can someone show me how to set any integer (or float) in an
>>> std::vector as zero in a way other than using a for loop? Can we
>>> apply memset() or ZeroMemory() to the vector?
>>
>> No.
>>
> Hmmm.... the question says how to initialize the vector. So would not
> this satisfy the question:
>
> std::vector<int> v;
> v.resize(100);
>
> Thus creating 100 elements that are all default initialized, or 0
> initialized in the case of ints.

If it's initialization, then

std::vector<int> v(100);

will do it without a resize.


--
John Carson

"John Carson" <jcarson_n_o_sp_am_@netspace.net.au> wrote in message
news:45b1f4aa$0$11211$
> "JDT" <> wrote in message
> news:ZKfsh.68668$. net
>> Hi,
>>
>> Can someone show me how to set any integer (or float) in an
>> std::vector as zero in a way other than using a for loop? Can we
>> apply memset() or ZeroMemory() to the vector? Thanks for your help.
>>
>> JD
>
>
> For a vector with 100 zeros:
>
> vector<int> v(100,0);

vector<int> v(100);

will also do it, but the OP may not want initialization.


--
John Carson

Ivan Novick wrote:
> Victor Bazarov wrote:
>> JDT wrote:
>>> Can someone show me how to set any integer (or float) in an
>>> std::vector as zero in a way other than using a for loop? Can we
>>> apply memset() or ZeroMemory() to the vector?
>>
>> No.
>>
> Hmmm.... the question says how to initialize the vector.

No, it doesn't. It asks how to "set any integer".

> So would not
> this satisfy the question:
>
> std::vector<int> v;
> v.resize(100);
>
> Thus creating 100 elements that are all default initialized, or 0
> initialized in the case of ints.

Just to explain to those who missed it, the "no" is for the last
question (about 'memset' or 'ZeroMemory' application to a vector).
I hope it's clearer now.

My answer to how to set the contents of the vector to 0 was given
in the same message and for whatever reason snipped away by Ivan.

V
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