[英]visibility among templated classes
顧名思義,我有兩個類TwoWayVector和TwoWayVectorIterator,我正在嘗試實現自己的向量類和一個迭代器。 我似乎遇到了一些可見性問題,並且我也不確定如何從TwoWayVector.begin()方法構造一個TwoWayVectorIterator。
TwoWayVector.cc
#include <sstream>
using namespace std;
template <class T> class TwoWayVector{
public:
T* data;
int capacity;
int nextFree;
TwoWayVector(){
capacity = 10;
nextFree = 0;
data = new T[capacity];
}
~TwoWayVector(){
delete data;
}
T& operator[](const int index){
if( index >= capacity || capacity + index < 0){
string number = static_cast<ostringstream*>( &(ostringstream() << index) )->str();
string error = "index " + number + " is out of bounds";
throw error;
}
else if(index < 0){
return data[nextFree+index];
}
return data[index];
}
//memory leaks?
void push_back(T object){
if(capacity <= nextFree){
capacity = capacity*2;
T* tmp = new T[capacity];
for(int i=0; i<capacity; i++){
tmp[i] = data[i];
}
delete data;
data = tmp;
}
data[nextFree] = object;
nextFree++;
}
T pop_back(){
nextFree--;
T result = data[nextFree];
data[nextFree] = NULL;
return result;
}
int size(){
return nextFree;
}
TwoWayVectorIterator begin(){
TwoWayVectorIterator<T> iterator= new TwoWayVectorIterator<T>(0,this);
return (iterator);
}
};
TwoWayVectorIterator.cc
using namespace std;
template <class T> class TwoWayVectorIterator{
public:
TwoWayVector<T>* vector;
int currentPosition;
TwoWayVectorIterator(TwoWayVector<T>& vec){
currentPosition = 0;
vector = vec;
}
TwoWayVectorIterator( int pos , TwoWayVector<T>& vec){
currentPosition = pos;
vector = vec;
}
bool& operator==(const TwoWayVectorIterator* vector2){
bool address, position;
address = (&vector == &vector2) ? true : false;
position =(currentPosition == vector2->currentPosition) ? true : false;
return (address && position);
}
bool& operator!=(const TwoWayVectorIterator* vector2){
bool address, position;
address = (&vector == &vector2) ? true : false;
position=(currentPosition == vector2->currentPosition) ? true : false;
return (address && position);
}
TwoWayVectorIterator& operator++(){
currentPosition = (currentPosition+1);
return *this;
}
TwoWayVectorIterator& operator++(int){
currentPosition = (currentPosition+1);
return *this;
}
TwoWayVectorIterator& operator=(TwoWayVectorIterator* vector2){
&vector = vector2;
currentPosition = vector2->currentPosition;
return *this;
}
TwoWayVectorIterator& operator+(int n){
currentPosition = currentPosition+n;
return *this;
}
TwoWayVectorIterator& operator-(int n){
currentPosition = currentPosition-n;
return *this;
}
bool& operator<(TwoWayVectorIterator* vector2){
return (currentPosition<vector2->currentPosition);
}
T& operator*(){
return vector[currentPosition];
}
};
從Test.cc調用
using namespace std;
#include <iostream>
#include "TwoWayVector.cc"
#include "TwoWayVectorIterator.cc"
int main(){
TwoWayVector<int> numbers;
numbers.push_back(3);
numbers.push_back(2);
numbers.size();
TwoWayVectorIterator current = numbers.begin();
return 0;
}
編譯器錯誤:
In file included from Test.cc:3:
TwoWayVector.cc:59: error: ‘TwoWayVectorIterator’ does not name a type
Test.cc: In function ‘int main()’:
Test.cc:18: error: missing template arguments before ‘current’
Test.cc:18: error: expected `;' before ‘current’
我已經嘗試過聲明兩種不同的方式,不同的包含方案,並調用TwoWayVectorIterator current = numbers.begin(),但是我不想指定迭代器的類型。
非常感謝您的任何幫助!!
第一個問題:
似乎您沒有#include
包含文件TwoWayVector.cc
包含TwoWayVectorIterator
定義的文件,該文件在函數begin()
使用其定義。
嘗試添加以下指令:
#include <sstream>
#include "TwoWayVectorIterator.cc"
^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
第二個問題:
在TwoWayVectorIterator.cc
,您將必須提交一個前向聲明以使其意識到TwoWayVector
的存在:
template<typename T> class TwoWayVector;
第三個問題:
另外,在函數begin()
您使用TwoWayVectorIterator
作為返回類型,而沒有指定必要的模板參數:
TwoWayVectorIterator<T> begin(){
// ^^^
TwoWayVectorIterator<T> iterator= new TwoWayVectorIterator<T>(0,this);
return (iterator);
}
第四個問題:
您的main()
函數遇到類似的問題:
int main()
{
TwoWayVector<int> numbers;
// ...
TwoWayVectorIterator<int> current = numbers.begin();
// ^^^^^
// ...
}
第五題:
另一個問題是,構造TwoWayVectorIterator
應該接受一個指針 ,而不是一個參考, TwoWayVector
(至少從你如何使用它判斷):
TwoWayVectorIterator( int pos , TwoWayVector<T>* vec){
// ^^^^^^^^^^^^^^^^
currentPosition = pos;
vector = vec;
}
第六題:
operator ==
和operator !=
重載正在返回對臨時bool
對象的引用,該引用最終將在函數返回時被銷毀,從而給您留下了懸空的引用,並在嘗試取消引用它時導致未定義行為。
您應該只返回bool
:
bool operator==(const TwoWayVectorIterator* vector2){
// ^^^^
// Return by value here!
// ...
return (address && position);
}
bool operator!=(const TwoWayVectorIterator* vector2){
// ^^^^
// Return by value here!
// ...
return (address && position);
}
相關建議:
此外,應避免在全局名稱空間范圍內using
此類using
指令:
using namespace std;
這會將所有名稱從std
命名空間導入到全局命名空間,這可能導致不希望的名稱沖突。
作為進一步的一般建議,請避免為變量提供標准容器類的名稱(例如vector
)。 選擇像myVector
,或innerVector
,或任何你認為最適合作為一個描述性的名稱。
此外,您應該遵循命名約定,並分別給您的頭文件和實現文件擴展名,例如.h
(或.hpp
)和.cpp
。
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