C++ std::vector arguments in brackets - explanation?

Question

I am inexperienced at c++. I have come across the below code

std::vector<char> is_prime(sqrt + 1, 1);

Update Where sqrt is a positive integer.

I believe it is defining a vector filled with characters, naming the vector is_prime, but I don't understand what the purpose of the two arguments are.

I have had a look at the documentation for std::vector, however this wasn't clear to me. I have also searched SO but no question I found helped.

Example: say sqrt is 4, then this would be in effect:

is_prime(5, 1);

Does this mean it is a vector with elements 5 and 1? A vector with size 5 and first element 1?

The documentation you are looking for can be found at [std::vector::vector](http://en.cppreference.com/w/cpp/container/vector/vector). That constructor is the overload labeled `(2)`. — François Andrieux, Nov 03 '17 at 19:45
It’s a vector with 5 chars of value 1. Most likely someone didn’t like vector . — , Nov 03 '17 at 19:45

score 2 · Accepted Answer · answered Nov 03 '17 at 19:45

2

first argument is "Initial container size", second argument is "Value to fill the container with. Each of the n elements in the container will be initialized to a copy of this value."

http://www.cplusplus.com/reference/vector/vector/vector/

answered Nov 03 '17 at 19:45

Andrey Belykh

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https://stackoverflow.com/questions/6520052/whats-wrong-with-cplusplus-com – François Andrieux Nov 03 '17 at 19:46

score 0 · Answer 2 · answered Nov 03 '17 at 19:46

0

Probably the second form of vector's constructor http://www.cplusplus.com/reference/vector/vector/vector/

vector (size_type n, const value_type& val = value_type(),
             const allocator_type& alloc = allocator_type());

Which would fill a vector of characters with sqrt + 1 elements, all set to the whatever 1 is as a character.

answered Nov 03 '17 at 19:46

Christopher Pisz

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https://stackoverflow.com/questions/6520052/whats-wrong-with-cplusplus-com – François Andrieux Nov 03 '17 at 19:47
@Francois Not getting your reference. It's a link to someone asking what others don't like about cplusplus.com. It's closed as off topic. Are you trying to say that you dislike links to cplusplus.com? If so, then suggest a better reference. – Christopher Pisz Nov 03 '17 at 19:48

C++ std::vector arguments in brackets - explanation?

2 Answers2