Question

struct comp {
    long a;
    vector<int> b(9);
    bool c;
};

Errors:

code.cpp:67:19: error: expected identifier before numeric constant
code.cpp:67:19: error: expected ‘,’ or ‘...’ before numeric constant

What is wrong with this? Why doesn’t g++ accept if I say that b will have 9 elements?

Answer 1

Because C++ doesn’t work like that.

Initializers go in the initializer list of a constructor, e.g.

struct comp {
    long a;
    vector<int> b;
    bool c;

    comp() : b(9) { }
};

(Note that a class thus defined is no longer an aggregate.)

Note: C++11 adds member initializers, but only using copy-initialization syntax:

struct Foo {
    int a = 5;
    vector<char> b = vector<char>(8);
};

Compiler support for this is still incomplete.