关于在C++中将数组存储在std :: vector中的问题

Question

我不清楚以下情况.

首先,这段代码编译得很好:

#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);
}

以下代码几乎相同:

#include <vector>

typedef std::vector<int[4]> vec;

int main(){
    vec v;
    int a[4] = {0,1,2,3};
    v.push_back(a);
}

但它会抛出我将在最后包含的极长的错误输出.为什么编译器对这两个程序的处理方式如此不同？这绝对不直观.

这是我的系统上使用g ++编译时抛出的编译器错误:

[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]’

Answer 1

错误:ISO C++禁止在数组中初始化新
错误:数组必须使用大括号括起初始化程序
错误进行初始化:无效数组赋值
错误:请求'*__p'中的成员'~int [4]',这是非类输入'int [4]'

要了解其中一个错误,请想象以下内容:

void main() {
    int a[4] = {0,1,2,3};
    int b[4] = a;
}

相反:

typedef struct{
    int x1,x2,x3,x4;
}  ints;

int main()
{
    ints a;
    ints b = a;
}

甚至:

typedef struct{
    int x[4];
}  ints;

int main()
{
    ints a;
    ints b = a;
}

不能通过赋值运算符复制C/C++数组,尽管struct包含数组的s可以.
所以一个简单的解决方法是:

typedef struct{
        int x[4];
}  ints;

typedef std::vector<ints> vec;

int main(){
        vec v;
        ints a = { {0,1,2,3} };
        v.push_back(a);
}

Answer 2

在引擎盖下,它正在进行分配,而没有为数组定义.

错误的相关部分是

从这里实例化/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:306:错误:必须使用大括号括起初始化程序初始化数组 /usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/stl_vector .h:741:从'void std :: vector <_Tp,_Alloc> :: push_back(const _Tp&)[with _Tp = int [4],_ Alloc = std :: allocator]'test2.cpp:9实例化实例化这里/usr/lib/gcc/i586-redhat-linux/4.4.1/../../../../include/c++/4.4.1/bits/vector.tcc:312:错误:数组无效分配

Answer 3

尝试使用boost :: array而不是普通数组.它提供了固定大小数组周围的STL兼容接口,因此可以在STL容器中使用.另外,它实现了边界检查(boost::array::at).

#include <boost/array.hpp>
#include <vector>

typedef std::vector< boost::array<int, 4> > vec;
int main(){
    vec v;
    boost::array<int, 4> va = {0,1,2,3};
    v.push_back(va);
}