Correct way to work with vector of arrays

Question

Could someone tell what is the correct way to work with a vector of arrays?

I declared a vector of arrays (vector<float[4]>) but got error: conversion from 'int' to non-scalar type 'float [4]' requested when trying to resize it. What is going wrong?

Answer 1

Use:

vector<vector<float>> vecArray; //both dimensions are open!

Answer 2

You cannot store arrays in a vector or any other container. The type of the elements to be stored in a container (called the container's value type) must be both copy constructible and assignable. Arrays are neither.

You can, however, use an array class template, like the one provided by Boost, TR1, and C++0x:

std::vector<std::array<double, 4> >

(You'll want to replace std::array with std::tr1::array to use the template included in C++ TR1, or boost::array to use the template from the Boost libraries. Alternatively, you can write your own; it's quite straightforward.)

Answer 3

There is no error in the following piece of code:

float arr[4];
arr[0] = 6.28;
arr[1] = 2.50;
arr[2] = 9.73;
arr[3] = 4.364;
std::vector<float*> vec = std::vector<float*>();
vec.push_back(arr);
float* ptr = vec.front();
for (int i = 0; i < 3; i++)
    printf("%g\n", ptr[i]);

OUTPUT IS:

6.28

2.5

9.73

4.364

IN CONCLUSION:

std::vector<double*>

is another possibility apart from

std::vector<std::array<double, 4>>

that James McNellis suggested.

Answer 4

Every element of your vector is a float[4], so when you resize every element needs to default initialized from a float[4]. I take it you tried to initialize with an int value like 0?

Try:

static float zeros[4] = {0.0, 0.0, 0.0, 0.0};
myvector.resize(newsize, zeros);