C++/Size of a 2d vector
Solution 1
To get the size of v2d, simply use v2d.size(). For size of each vector inside v2d, use v2d[k].size().
Note: for getting the whole size of v2d
, sum up the size of each individual vector, as each vector has its own size.
Solution 2
You had some errors in your code, which I've fixed and commented on below.
vector < vector <int> > v2d;
for (int x = 0; x < 3; x++)
{
// Move push_back() into the outer loop so it's called once per
// iteration of the x-loop
v2d.push_back(vector <int> ());
for (int y = 0; y < 5; y++)
{
v2d[x].push_back(y);
}
}
cout<<v2d.size()<<endl; // Remove the [0]
cout<<v2d[0].size()<<endl; // Remove one [0]
v2d.size()
returns the number of vectors in the 2D vector. v2d[x].size()
returns the number of vectors in "row" x
. If you know the vector is rectangular (all "rows" are of the same size), you can get the total size with v2d.size() * v2d[0].size()
. Otherwise you need to loop through the "rows":
int size = 0;
for (int i = 0; i < v2d.size(); i++)
size += v2d[i].size();
As a change, you can also use iterators:
int size = 0;
for (vector<vector<int> >::const_iterator it = v2d.begin(); it != v2d.end(); ++it)
size += it->size();
Solution 3
The vector<vector<int>>
does not have a whole size, because each vector within it has an independent size. You need to sum the size of all contained vectors.
int size = 0;
for(int i = 0; i < v2d.size(); i++)
size += v2d[i].size();
Solution 4
int size_row = v2d.size();
int size_col = v2d[0].size();
pandoragami
My name is Andrew Somorjai. I usually code with C++, x86 Assembler, Python, Java, JavaScript, HTML, CSS and Erlang.
Updated on April 10, 2020Comments
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pandoragami about 4 years
How do I find the size of a 2 dimensional vector? So far I have the following code which doesn't compile.
#include <iostream> #include <vector> using namespace std; int main() { vector < vector <int> > v2d; for (int x = 0; x < 3; x++) { for (int y = 0; y < 5; y++) { v2d.push_back(vector <int> ()); v2d[x].push_back(y); } } cout<<v2d[0].size()<<endl; cout<<v2d[0][0].size()<<endl; return 0; }
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moinudin over 13 yearsRemember the dreaded space!
vector<vector<int> >
, notvector<vector<int>>
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Puppy over 13 years@marcog: How old is your compiler? I'm pretty sure that hasn't been necessary since C++98.
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moinudin over 13 yearsThe reqirement for the space has only been dropped in C++0x. Leaving it out is a compile error using GCC. See ideone.com/mGdWb