c++ stl源码剖析学习笔记，一uninitialized_copy
template <class InputIterator, class ForwardIterator>
inline ForwardIterator uninitialized_copy(InputIterator first, InputIterator last,ForwardIterator result)
函数使用示例
#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <tuple>
#include <vector>
class Int{
public:
Int(int x):val(x){}
int get(){return val;}
private:
int val;
};
int main()
{
int A1[]={1,2,3,4,5,6,7};
const int N = sizeof(A1)/sizeof(Int);
Int* A2=(Int*)malloc(N * sizeof(Int));
std::uninitialized_copy(A1,A1+N,A2);
for(int i = 0 ; i < N ;++i){
std::cout << A2[i].get() << " ";
}
}
uninitialized_copy在A2的地址上初始化了一系列Int元素，数据的拷贝来源是 A1数组
跟进源码来查看uninitialized_copy()的工作流程(源码 stl源码剖析随书代码 tass-sgi-stl-2.91.57-source)
template <class InputIterator, class ForwardIterator>
inline ForwardIterator uninitialized_copy(InputIterator first, InputIterator last, ForwardIterator result)
--->
__uninitialized_copy(first, last, result, value_type(result));
--->
__uninitialized_copy_aux(first, last, result, is_POD());
--->
template <class InputIterator, class ForwardIterator>
inline ForwardIterator
__uninitialized_copy_aux(InputIterator first, InputIterator last,
ForwardIterator result,
__true_type) {
return copy(first, last, result);
}
template <class InputIterator, class ForwardIterator>
ForwardIterator
__uninitialized_copy_aux(InputIterator first, InputIterator last,
ForwardIterator result,
__false_type) {
ForwardIterator cur = result;
__STL_TRY {
for ( ; first != last; ++first, ++cur)
construct(&*cur, *first);
return cur;
}
__STL_UNWIND(destroy(result, cur));
}
主要便是uninitialized_copy()调用__uninitialized_copy() 最后一个参数是value_type(result)
value_type(result)的作用是将 ForwardIterator result 转化为指针类型T
__uninitialized_copy() 中调用__uninitialized_copy_aux() 则是判断 T是否为POD type
如何判断是否是POD type？
typedef typename __type_traits<T>::is_POD_type is_POD;
所有的基本类型都有如下定义
struct __type_traits<char> {
typedef __true_type is_POD_type;
};
struct __type_traits<signed char> {
typedef __true_type is_POD_type;
};
struct __type_traits<int> {
typedef __true_type is_POD_type;
};
而非基本类型则会对应到以下模板代码
template <class type>
struct __type_traits {
typedef __false_type is_POD_type;
};
所以当typename __type_traits<T>::is_POD_type的T 为int char double 等类型
is_POD_type为__true_type
其他类型则
is_POD_type为__false_type
如果是POD type，就是基本数据类型(int char double等)那么就直接拷贝即可
代码如下
__true_type
return copy(first, last, result);
如果不是POD type 就需要依次调用构造函数创建数据
代码如下
__false_type
for ( ; first != last; ++first, ++cur)
construct(&*cur, *first);
