I am unclear about the following.
First, this code compiles fine:
#include <vector>
typedef struct{
int x1,x2,x3,x4;
} ints;
typedef std::vector<ints> vec;
int main(){
vec v;
ints a = {0,1,2,3};
v.push_back(a);
}
The following code is near identical:
#include <vector>
typedef std::vector<int[4]> vec;
int main(){
vec v;
int a[4] = {0,1,2,3};
v.push_back(a);
}
but it throws the extremely length error output I will include at the end. Why does the compiler treat these two programs so differently? It is definitely not intuitive.
Here is the compiler error that is thrown on my system that is using g++ to compile:
[mattg@pigott Test]$ g++ test2.cpp -o test2
In file included from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/i586-redhat-linux/bits/c++allocator.h:34,
from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/allocator.h:48,
from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/vector:62,
from test2.cpp:2:
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = int [4]]’:
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/stl_vector.h:737: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int [4], _Alloc = std::allocator<int [4]>]’
test2.cpp:9: instantiated from here
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/ext/new_allocator.h:105: error: ISO C++ forbids initialization in array new
In file included from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/vector:69,
from test2.cpp:2:
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc: In member function ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = int [4], _Alloc = std::allocator<int [4]>]’:
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/stl_vector.h:741: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int [4], _Alloc = std::allocator<int [4]>]’
test2.cpp:9: instantiated from here
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:306: error: array must be initialized with a brace-enclosed initializer
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/stl_vector.h:741: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int [4], _Alloc = std::allocator<int [4]>]’
test2.cpp:9: instantiated from here
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:312: error: invalid array assignment
In file included from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/i586-redhat-linux/bits/c++allocator.h:34,
from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/allocator.h:48,
from /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/vector:62,
from test2.cpp:2:
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::destroy(_Tp*) [with _Tp = int [4]]’:
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:353: instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = int [4], _Alloc = std::allocator<int [4]>]’
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/stl_vector.h:741: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int [4], _Alloc = std::allocator<int [4]>]’
test2.cpp:9: instantiated from here
/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/ext/new_allocator.h:115: error: request for member ‘~int [4]’ in ‘* __p’, which is of non-class type ‘int [4]’
Under the hood it's doing an assignment and that isn't defined for arrays.
The pertinent part of the error is
instantiated from here /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:306: error: array must be initialized with a brace-enclosed initializer /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/stl_vector.h:741: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = int [4], _Alloc = std::allocator]’ test2.cpp:9: instantiated from here /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:312: error: invalid array assignment