Error trying to access a struct type using a pointer to a vector of structs

Question

#include <iostream>
#include <vector>
using namespace std;

struct a_struct { int an_int; };

int main () 
{
    vector <vector <a_struct> > the_vec;
    vector <a_struct> * p_vs;
    p_vs = & the_vec[0];
    *(p_vs)[0].an_int=0;   //error: 'class __gnu_debug_def::vector<a_struct,
                           //std::allocator<a_struct> >' has no member named 'an_int'
}

I can't figure out why I'm getting the above compile error.

The error message is telling you that *(p_vs)[0] has type vector<a_struct>. — Ray Toal
– Ray Toal, Commented Oct 1, 2011 at 6:39
@Ray That shouldn't be the case. How does that follow from the code? — Matt Munson
– Matt Munson, Commented Oct 1, 2011 at 6:43

Ray Toal · Accepted Answer · 2011-10-01 06:42:51Z

2

In C++, [] and . have higher precedence than *.

Your last line

*(p_vs)[0].an_int=0;

when fully parenthesized, is

*((p_vs[0]).an_int)=0;

Since p_vs was declared as

vector <a_struct> * p_vs;

it is as if p_vs is an array of vector <a_struct> elements, so p_vs[0] is a vector<a_struct>.

And vector<a_struct> objects indeed do not have a member an_int.

Add some parens and you will get what you want.

answered Oct 1, 2011 at 6:42

Ray Toal

88.7k20 gold badges186 silver badges245 bronze badges

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

1 Comment

Matt Munson Over a year ago

Ok, I see. The * goes inside the parens. Thanks.

Collectives™ on Stack Overflow

Error trying to access a struct type using a pointer to a vector of structs

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related