我如何连接两个std::向量?
当前回答
对于提供push_back (string, vector, deque，…)功能的容器:
Std::copy(Std::begin(input)， Std::end(input)， Std::back_inserter(output))
and
对于提供insert (map, sets)功能的容器:
Std::copy(Std::begin(input)， Std::end(input)， Std::inserter(output, output.end()))
其他回答
对于提供push_back (string, vector, deque，…)功能的容器:
Std::copy(Std::begin(input)， Std::end(input)， Std::back_inserter(output))
and
对于提供insert (map, sets)功能的容器:
Std::copy(Std::begin(input)， Std::end(input)， Std::inserter(output, output.end()))
我已经实现了这个函数，它连接任何数量的容器，从右值引用移动和复制
namespace internal {
// Implementation detail of Concatenate, appends to a pre-reserved vector, copying or moving if
// appropriate
template<typename Target, typename Head, typename... Tail>
void AppendNoReserve(Target* target, Head&& head, Tail&&... tail) {
// Currently, require each homogenous inputs. If there is demand, we could probably implement a
// version that outputs a vector whose value_type is the common_type of all the containers
// passed to it, and call it ConvertingConcatenate.
static_assert(
std::is_same_v<
typename std::decay_t<Target>::value_type,
typename std::decay_t<Head>::value_type>,
"Concatenate requires each container passed to it to have the same value_type");
if constexpr (std::is_lvalue_reference_v<Head>) {
std::copy(head.begin(), head.end(), std::back_inserter(*target));
} else {
std::move(head.begin(), head.end(), std::back_inserter(*target));
}
if constexpr (sizeof...(Tail) > 0) {
AppendNoReserve(target, std::forward<Tail>(tail)...);
}
}
template<typename Head, typename... Tail>
size_t TotalSize(const Head& head, const Tail&... tail) {
if constexpr (sizeof...(Tail) > 0) {
return head.size() + TotalSize(tail...);
} else {
return head.size();
}
}
} // namespace internal
/// Concatenate the provided containers into a single vector. Moves from rvalue references, copies
/// otherwise.
template<typename Head, typename... Tail>
auto Concatenate(Head&& head, Tail&&... tail) {
size_t totalSize = internal::TotalSize(head, tail...);
std::vector<typename std::decay_t<Head>::value_type> result;
result.reserve(totalSize);
internal::AppendNoReserve(&result, std::forward<Head>(head), std::forward<Tail>(tail)...);
return result;
}
或者你可以用:
std::copy(source.begin(), source.end(), std::back_inserter(destination));
如果两个向量不包含完全相同类型的内容，则此模式非常有用，因为您可以使用某些内容而不是std::back_inserter来从一种类型转换为另一种类型。
std::vector<int> first;
std::vector<int> second;
first.insert(first.end(), second.begin(), second.end());
你可以为+操作符准备自己的模板:
template <typename T>
inline T operator+(const T & a, const T & b)
{
T res = a;
res.insert(res.end(), b.begin(), b.end());
return res;
}
接下来，使用+:
vector<int> a{1, 2, 3, 4};
vector<int> b{5, 6, 7, 8};
for (auto x: a + b)
cout << x << " ";
cout << endl;
这个例子给出了输出:
1 2 3 4 5 6 7 8
