Error in Initializing a vector of structures with a size

Question

I have a struct as defined below

struct valindex {
    int x;
    int y;
    valindex(int val, int index) : x(val), y(index) {}
};

I'm getting an error when trying to initialize a vector of this struct

vector<valindex> vals() // this works fine
vector<valindex> vals(20) // throws the error mentioned below when the size is specified

required from 'static _ForwardIterator std::__uninitialized_default_n_1<_TrivialValueType>::__uninit_default_n(_ForwardIterator, _Size) [with _ForwardIterator = valindex*; _Size = long unsigned int; bool _TrivialValueType = false]'

Can someone explain the cause of this error and provide a solution?

Thanks!

Youre missing part of the error but more importantly the first version only "works" because it doesnt do what you think it does. Lookup Most Vexing Parse. The problem is your type doesnt have a default constructor and youre trying to create 20 default objects of that type. — Borgleader
– Borgleader, Commented Jun 26, 2017 at 20:24
Thanks . I missed adding the default constructor and couldn't figure that out from the error message. — Sumit Das
– Sumit Das, Commented Jun 26, 2017 at 20:30

R Sahu · Accepted Answer · 2017-06-26 20:30:44Z

3

vector<valindex> vals();

works because it declares a function named vals that takes no arguments and returns a vector<valindex>. See https://en.wikipedia.org/wiki/Most_vexing_parse.

vector<valindex> vals(20);

does not work since it tries construct a vector of valindex and one of the requirements of creating such an object is that valindex be default-constructible. Since valindex is not default-constructible, that line cannot be compiled.

answered Jun 26, 2017 at 20:30

R Sahu

207k15 gold badges168 silver badges291 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Андрей Чистобаев · Accepted Answer · 2017-06-26 22:01:35Z

0

std::vector has another helpful constructor:

std::vector vals(999, {11, 55});

Vector vals will store 999 copies of valindex(11, 55). Welcome to c++11!

answered Jun 26, 2017 at 22:01

Андрей Чистобаев

155 bronze badges

2 Comments

jspurim Over a year ago

Hello, welcome to the site. Please read this markdown tutorial to learn how to format code in your answers.

jspurim Over a year ago

Also, keep in mind the OP is asking for an explanation of the error as well as a solution, consider providing that too.

Collectives™ on Stack Overflow

Error in Initializing a vector of structures with a size

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related