constructing nested vectors

[Anjo Gasa]

If I have the following class member:

std::vector<float> singleVector;

I can initialize it to have 50 elements with values of 0.5:

singleVector = std::vector<float>( 50, 0.5 );

My question concerns when I move to using this class member:

std::vector<std::vector<float>> nestedVector;

and attempt to initialize:

nestedVector = std::vector<std::vector<float>>( 50,
std::vector<float>( 10, 0.5 ) );

which I would expect would initialize the vector to have 50 nested
vectors, each having 10 elements with values of 0.5.

This does not, however, compile.

Anjo

 

[Alf P. Steinbach]

* Anjo Gasa:

If I have the following class member:

std::vector<float> singleVector;

I can initialize it to have 50 elements with values of 0.5:

singleVector = std::vector<float>( 50, 0.5 );

My question concerns when I move to using this class member:

std::vector<std::vector<float>> nestedVector;

and attempt to initialize:

nestedVector = std::vector<std::vector<float>>( 50,
std::vector<float>( 10, 0.5 ) );

which I would expect would initialize the vector to have 50 nested
vectors, each having 10 elements with values of 0.5.

This does not, however, compile.

Spaces are extra cheap these days, try one!

Cheers,

- Alf

 

[BobR]

If I have the following class member:
std::vector<float> singleVector;
I can initialize it to have 50 elements with values of 0.5:
singleVector = std::vector<float>( 50, 0.5 );
My question concerns when I move to using this class member:
std::vector<std::vector<float>> nestedVector;
and attempt to initialize:
nestedVector = std::vector<std::vector<float>>( 50,
std::vector<float>( 10, 0.5 ) );
which I would expect would initialize the vector to have 50 nested
vectors, each having 10 elements with values of 0.5.
This does not, however, compile.
Anjo

If possible, do it all in one shot:

std::vector<std::vector<float> > nestedVector( 50,
std::vector<float>( 10, 0.5 ) );

Note what Alf said about the 'space':

// .....float>> // no space, no good
.....float> > // that's '>' + ' ' + '>'

Otherwise it's taken as a 'right-shift'(7 >> 2) or 'insertion'(cin >>
intvar) operator, and the compiler has a heart attack because it can't
figure out what you are trying to shift/insert from-to.