CODEWITHSUNDEEP
c++arraysvector
godse121
godse121

Reputation: 11

declaring array of vectors in cpp

I am new to cpp STL I have a doubt regarding array of vectors when we declare array of vectors like vectors <int> arr[100]; we can also say this as a 2-D matrix .But we if talk about 2-D arrays (int prr[100][100]) then prr[0] then it will print the address of first array in 0th row Basically i want to ask why we are declaring vector <int> arr[100] because arr[0] will also store address of array at 0th array we should declare like vector <int*> arr[100] for declaring array of vectors

Upvotes: 1

Views: 468

Answers (1)

R Sahu
R Sahu

Reputation: 206717

But we if talk about 2-D arrays (int prr[100][100]) then prr[0] then it will print the address of first array in 0th row

That is true to some extent and in some contexts.

prr[0] is an object of type int [100] -- an array of 100 ints.

In some contexts, prr[0] decays to a pointer to its first element, however it is not always true.

sizeof(prr[0]) will be 100 * sizeof(int).
&prr[0] will be of type int (*)[100), pointer to "array of 100 ints", not int**.

In contrast,

Basically i want to ask why we are declaring vector <int> arr[100] because arr[0] will also store address of array at 0th array we should declare likevector <int*> arr[100] for declaring array of vectors

No, arr[0] will not store the address of the array at 0-th array. arr[0] is of type std::vector<int>. It's simple as that. Unlike an array, an object of type std::vector<int> does not decay to a pointer to the first element of the object in any context. Hence any further comparisons with int* does not make sense.

Upvotes: 3

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