如果在数组中传递的项目已经存在,则抛出数据异常 [英] Throwing a data exception if item passed in array already exists
问题描述
我正在尝试编写一个函数来检测在数组中传递的项是否已经存在,
I am trying to write a function that detects if an item that is passed in an array already exists,
这是我已经拥有的一个函数,如果超出了数组的容量,该函数将引发异常,我不确定如何编写一个函数来检测传入的项是否已经存在.
here is a function I already had that would throw an exception if the capacity of the array was exceeded, I am unsure how to write a function that would detect if an item passed in already exists.
template<class ItemType>
void ArraySet<ItemType>::add(const ItemType& newEntry) {
if (itemCount >= maxItems) {
throw ExceededCapacityError();
} else {
items[itemCount] = newEntry;
itemCount++;
}
}
更新:代码可以编译,但最终会出现未处理的异常错误
Update: code compiles but end up getting unhandled exception error
错误:ArraySetV1.exe中0x74E440B2处未处理的异常:Microsoft C ++异常:cs_set :: ArraySetstd :: basic_string< char,std :: char_traits< char,std :: allocator>> :: DuplicateItemError位于内存位置0x00AFF577.
Error: Unhandled exception at 0x74E440B2 in ArraySetV1.exe: Microsoft C++ exception: cs_set::ArraySetstd::basic_string<char,std::char_traits<char,std::allocator > >::DuplicateItemError at memory location 0x00AFF577.
template<class ItemType>
void ArraySet<ItemType>::add(const ItemType& newEntry) {
auto result1 = std::find(std::begin(items), std::end(items), newEntry);
if (std::begin(items) == std::end(items)) {
throw DuplicateItemError();
} else {
items[itemCount] = newEntry;
itemCount++;
}
}
尝试/捕获主要使用的内容:
Try / Catch used in main:
try {
cout << "Try to add another entry: add(\"extra\")... ";
set.add("extra");
cout << "should cause exception but didn't" << endl;
} catch (ArraySet<string>::DuplicateItemError e) {
cout << "should cause exception!" << endl;
}
这是我的第一个头文件:
Here is my first header file:
namespace cs_set {
template<class ItemType>
void ArraySet<ItemType>::add(const ItemType& newEntry) {
auto result1 = std::find(std::begin(items), std::end(items), newEntry);
if (result1 == std::end(items)) {
throw DuplicateItemError();
} else { //Error
items[itemCount] = newEntry;
itemCount++;
}
}
template<class ItemType>
ArraySet<ItemType>::ArraySet() {
itemCount = 0;
maxItems = DEFAULT_CAPACITY;
}
template<class ItemType>
int ArraySet<ItemType>::getCurrentSize() const {
return itemCount;
}
template<class ItemType>
bool ArraySet<ItemType>::isEmpty() const {
return itemCount == 0;
}
template<class ItemType>
std::vector<ItemType> ArraySet<ItemType>::toVector() const {
std::vector<ItemType> setContents;
for (int i = 0; i < itemCount; i++) {
setContents.push_back(items[i]);
}
return setContents;
}
template <class ItemType>
bool ArraySet<ItemType>::contains(const ItemType& anEntry) const {
bool isFound = false;
int curIndex = 0;
while (!isFound && (curIndex < itemCount)) {
isFound = (anEntry == items[curIndex]);
if (!isFound) {
curIndex++;
}
}
return isFound;
}
template<class ItemType>
void ArraySet<ItemType>::clear() {
itemCount = 0;
}
template<class ItemType>
int ArraySet<ItemType>::getIndexOf(const ItemType& target) const {
bool isFound = false;
int result = -1;
int searchIndex = 0;
while (!isFound && (searchIndex < itemCount)) {
isFound = (items[searchIndex] == target);
if (isFound) {
result = searchIndex;
} else {
searchIndex++;
}
}
return result;
}
template<class ItemType>
void ArraySet<ItemType>::remove(const ItemType& anEntry) {
int locatedIndex = getIndexOf(anEntry);
if (locatedIndex > -1) {
itemCount--;
items[locatedIndex] = items[itemCount];
} else {
throw ItemNotFoundError();
}
}
}
头文件:
#ifndef ARRAY_SET_
#define ARRAY_SET_
#include <algorithm>
#include <iterator>
#include "SetInterface.h"
namespace cs_set {
template<class ItemType>
class ArraySet : public SetInterface<ItemType>
{
public:
typedef ItemType value_type;
class DuplicateItemError {};
class ItemNotFoundError {};
ArraySet();
int getCurrentSize() const;
bool isEmpty() const;
void add(const ItemType& newEntry);
void remove(const ItemType& anEntry);
void clear();
bool contains(const ItemType& anEntry) const;
//int getFrequencyOf(const ItemType& anEntry) const;
std::vector<ItemType> toVector() const;
private:
static const int DEFAULT_CAPACITY = 6;
ItemType items[DEFAULT_CAPACITY];
int itemCount;
int maxItems;
// Returns either the index of the element in the array items that
// contains the given target or -1, if the array does not contain
// the target.
int getIndexOf(const ItemType& target) const;
};
}
#include "ArraySet.cpp"
#endif
另一个头文件:
#ifndef SET_INTERFACE
#define SET_INTERFACE
#include <vector>
#include <algorithm>
#include <iterator>
namespace cs_set {
template<class ItemType>
class SetInterface
{
public:
/** Gets the current number of entries in this bag.
@return The integer number of entries currently in the bag. */
virtual int getCurrentSize() const = 0;
/** Sees whether this bag is empty.
@return True if the bag is empty, or false if not. */
virtual bool isEmpty() const = 0;
/** Adds a new entry to this bag.
@post If successful, newEntry is stored in the bag and
the count of items in the bag has increased by 1.
@param newEntry The object to be added as a new entry.
@return True if addition was successful, or false if not. */
virtual void add(const ItemType& newEntry) = 0;
/** Removes one occurrence of a given entry from this bag,
if possible.
@post If successful, anEntry has been removed from the bag
and the count of items in the bag has decreased by 1.
@param anEntry The entry to be removed.
@return True if removal was successful, or false if not. */
virtual void remove(const ItemType& anEntry) = 0;
/** Removes all entries from this bag.
@post Bag contains no items, and the count of items is 0. */
virtual void clear() = 0;
/** Counts the number of times a given entry appears in this bag.
@param anEntry The entry to be counted.
@return The number of times anEntry appears in the bag. */
// virtual int getFrequencyOf(const ItemType& anEntry) const = 0;
/** Tests whether this bag contains a given entry.
@param anEntry The entry to locate.
@return True if bag contains anEntry, or false otherwise. */
virtual bool contains(const ItemType& anEntry) const = 0;
/** Empties and then fills a given vector with all entries that
are in this bag.
@return A vector containing all the entries in the bag. */
virtual std::vector<ItemType> toVector() const = 0;
/** Destroys this bag and frees its assigned memory. (See C++ Interlude 2.) */
virtual ~SetInterface() { }
};
}
#endif
主文件:
#include <iostream>
#include <string>
#include "ArraySet.h"
using std::cout;
using std::endl;
using std::string;
using namespace cs_set;
void displaySet(ArraySet<string>& set) {
cout << "The set contains " << set.getCurrentSize()
<< " items:" << endl;
std::vector<string> setItems = set.toVector();
int numEntries = setItems.size();
for (int i = 0; i < numEntries; i++) {
cout << setItems[i] << " ";
}
cout << endl << endl;
}
void setTester(ArraySet<string>& set)
{
cout << "isEmpty: returns " << set.isEmpty()
<< "; should be 1 (true)" << endl;
displaySet(set);
std::string items[] = {"one", "two", "three", "four", "five", "one"};
cout << "Add 6 items to the set: " << endl;
for (int i = 0; i < 6; i++) {
set.add(items[i]);
}
displaySet(set);
cout << "isEmpty: returns " << set.isEmpty()
<< "; should be 0 (false)" << endl;
cout << "getCurrentSize: returns " << set.getCurrentSize()
<< "; should be 6" << endl;
try {
cout << "Try to add another entry: add(\"extra\")... ";
set.add("extra");
cout << "should cause exception but didn't" << endl;
} catch (ArraySet<string>::DuplicateItemError e) {
cout << "should cause exception and did!" << endl;
}
displaySet(set);
}
int main()
{
ArraySet<string> set;
cout << "Testing the Array-Based Set:" << endl;
cout << "The initial set is empty." << endl;
setTester(set);
cout << "All done!" << endl;
}
推荐答案
最简单的方法是遍历每个现有元素,并在抛出异常时返回Exception或返回false.否则,您可以添加它.
The most trivial approach would be to iterate over every existing element and throw an Exception / return false when you find it. Otherwise you can add it.
尽管我建议您使用排序后的列表(例如: std :: set
),前提是您可以使用更改后的Elements顺序.
Though i'd recommend to use sorted Lists (e.g.: std::set
) if you can live with a changed order of Elements.
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