当我从txt文件输入位置时，我得到一个奇怪的错误，它似乎错过了第一个条目，但是在链接列表的末尾添加了一个垃圾条目（它被设计为取名，纬度和您将注意到的每个位置的经度）。我想这是一个问题，它开始收集输入和停止的地方，但我无法找到错误！它正确地读取了第一行但是在添加它之前跳到了下一行，因为在测试bug期间它没有第一个位置里斯本的记录，虽然进入方法调用它正在阅读它。非常离奇，但希望有人知道这个问题。首先是我的头文件：
#include <string>
struct locationNode
{
char nodeCityName [35];
double nodeLati;
double nodeLongi;
locationNode* Next;
void CorrectCase() // Correct upper and lower case letters of input
{
int MAX_SIZE = 35;
int firstLetVal = this->nodeCityName[0], letVal;
int n = 1; // variable for name index from second letter onwards
if((this->nodeCityName[0] >90) && (this->nodeCityName[0] < 123)) // First letter is lower case
{
firstLetVal = firstLetVal - 32; // Capitalise first letter
this->nodeCityName[0] = firstLetVal;
}
while(n <= MAX_SIZE - 1)
{
if((this->nodeCityName[n] >= 65) && (this->nodeCityName[n] <= 90))
{
letVal = this->nodeCityName[n] + 32;
this->nodeCityName[n] = letVal;
}
n++;
}
//cityNameInput = this->nodeCityName;
}
};
class Locations
{
private:
int size;
public:
Locations(){
}; // constructor for the class
locationNode* Head;
//int Add(locationNode* Item);
};
这是包含main的文件：
// U08221.cpp : main project file.
#include "stdafx.h"
#include "Locations.h"
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
int n = 0,x, locationCount = 0, MAX_SIZE = 35;
string cityNameInput;
char targetCity[35];
bool acceptedInput = false, userInputReq = true, match = false, nodeExists = false;// note: addLocation(), set to true to enable user input as opposed to txt file
locationNode *start_ptr = NULL; // pointer to first entry in the list
locationNode *temp, *temp2; // Part is a pointer to a new locationNode we can assign changing value followed by a call to Add
locationNode *seek, *bridge;
void setElementsNull(char cityParam[])
{
int y=0, count =0;
while(cityParam[y] != NULL)
{
y++;
}
while(y < MAX_SIZE)
{
cityParam[y] = NULL;
y++;
}
}
void addLocation()
{
temp = new locationNode; // declare the space for a pointer item and assign a temporary pointer to it
if(!userInputReq) // bool that determines whether user input is required in adding the node to the list
{
cout << endl << "Enter the name of the location: ";
cin >> temp->nodeCityName;
temp->CorrectCase();
setElementsNull(temp->nodeCityName);
cout << endl << "Please enter the latitude value for this location: ";
cin >> temp->nodeLati;
cout << endl << "Please enter the longitude value for this location: ";
cin >> temp->nodeLongi;
cout << endl;
}
temp->Next = NULL; //set to NULL as when one is added it is currently the last in the list and so can not point to the next
if(start_ptr == NULL){ // if list is currently empty, start_ptr will point to this node
start_ptr = temp;
}
else
{ temp2 = start_ptr;
// We know this is not NULL - list not empty!
while (temp2->Next != NULL)
{
temp2 = temp2->Next; // Move to next link in chain until reach end of list
}
temp2->Next = temp;
}
++locationCount; // increment counter for number of records in list
if(!userInputReq){
cout << "Location sucessfully added to the database! There are " << locationCount << " location(s) stored" << endl;
}
}
void populateList(){
ifstream inputFile;
inputFile.open ("locations.txt", ios::in);
userInputReq = true;
temp = new locationNode; // declare the space for a pointer item and assign a temporary pointer to it
do
{
inputFile.get(temp->nodeCityName, 35, ' ');
setElementsNull(temp->nodeCityName);
inputFile >> temp->nodeLati;
inputFile >> temp->nodeLongi;
setElementsNull(temp->nodeCityName);
if(temp->nodeCityName[0] == 10) //remove linefeed from input
{
for(int i = 0; temp->nodeCityName[i] != NULL; i++)
{
temp->nodeCityName[i] = temp->nodeCityName[i + 1];
}
}
addLocation();
}
while(!inputFile.eof());
userInputReq = false;
cout << "Successful!" << endl << "List contains: " << locationCount << " entries" << endl;
cout << endl;
inputFile.close();
}
bool nodeExistTest(char targetCity[]) // see if entry is present in the database
{
match = false;
seek = start_ptr;
int letters = 0, letters2 = 0, x = 0, y = 0;
while(targetCity[y] != NULL)
{
letters2++;
y++;
}
while(x <= locationCount) // locationCount is number of entries currently in list
{
y=0, letters = 0;
while(seek->nodeCityName[y] != NULL) // count letters in the current name
{
letters++;
y++;
}
if(letters == letters2) // same amount of letters in the name
{
y = 0;
while(y <= letters) // compare each letter against one another
{
if(targetCity[y] == seek->nodeCityName[y])
{
match = true;
y++;
}
else
{
match = false;
y = letters + 1; // no match, terminate comparison
}
}
}
if(match)
{
x = locationCount + 1; //found match so terminate loop
}
else{
if(seek->Next != NULL)
{
bridge = seek;
seek = seek->Next;
x++;
}
else
{
x = locationCount + 1; // end of list so terminate loop
}
}
}
return match;
}
void deleteRecord() // complete this
{
int junction = 0;
locationNode *place;
cout << "Enter the name of the city you wish to remove" << endl;
cin >> targetCity;
setElementsNull(targetCity);
if(nodeExistTest(targetCity)) //if this node does exist
{
if(seek == start_ptr) // if it is the first in the list
{
junction = 1;
}
if(seek != start_ptr && seek->Next == NULL) // if it is last in the list
{
junction = 2;
}
switch(junction) // will alter list accordingly dependant on where the searched for link is
{
case 1:
start_ptr = start_ptr->Next;
delete seek;
--locationCount;
break;
case 2:
place = seek;
seek = bridge;
delete place;
--locationCount;
break;
default:
bridge->Next = seek->Next;
delete seek;
--locationCount;
break;
}
}
else
{ cout << targetCity << "That entry does not currently exist" << endl << endl << endl;
}
}
void searchDatabase()
{
char choice;
cout << "Enter search term..." << endl;
cin >> targetCity;
if(nodeExistTest(targetCity))
{
cout << "Entry: " << endl << endl;
}
else
{
cout << "Sorry, that city is not currently present in the list." << endl << "Would you like to add this city now Y/N?" << endl;
cin >> choice;
/*while(choice != ('Y' || 'N'))
{
cout << "Please enter a valid choice..." << endl;
cin >> choice;
}*/
switch(choice)
{
case 'Y':
addLocation();
break;
case 'N':
break;
default :
cout << "Invalid choice" << endl;
break;
}
}
}
void printDatabase()
{
temp = start_ptr; // set temp to the start of the list
do
{ if (temp == NULL)
{
cout << "You have reached the end of the database" << endl;
}
else
{ // Display details for what temp points to at that stage
cout << "Location : " << temp->nodeCityName << endl;
cout << "Latitude : " << temp->nodeLati << endl;
cout << "Longitude : " << temp->nodeLongi << endl;
cout << endl;
// Move on to next locationNode if one exists
temp = temp->Next;
}
}
while (temp != NULL);
}
void nameValidation(string name)
{
n = 0; // start from first letter
x = name.size();
while(!acceptedInput)
{
if((name[n] >= 65) && (name[n] <= 122)) // is in the range of letters
{
while(n <= x - 1)
{
while((name[n] >=91) && (name[n] <=97)) // ERROR!!
{
cout << "Please enter a valid city name" << endl;
cin >> name;
}
n++;
}
}
else {
cout << "Please enter a valid city name" << endl;
cin >> name;
}
if(n <= x - 1)
{
acceptedInput = true;
}
}
cityNameInput = name;
}
int main(array<System::String ^> ^args)
{
//main contains test calls to functions at present
cout << "Populating list...";
populateList();
printDatabase();
deleteRecord();
printDatabase();
cin >> cityNameInput;
}
文本文件包含此内容（忽略名称，它们仅用于测试!!）：
Lisbon 45 47
Fattah 45 47
Darius 42 49
Peter 45 27
Sarah 85 97
Michelle 45 47
John 25 67
Colin 35 87
Shiron 40 57
George 34 45
Sean 22 33
输出省略了里斯本，但增加了一个带有无意义值的垃圾输入。有什么想法吗？提前谢谢。
答案 0 :(得分：1)
main函数创建一个新的locationNode并将其存储在全局变量temp中，然后读取第一个数据集并将其存储在该节点中。
然后，您致电addLocation()，首先创建另一个新locationNode，替换temp中的现有temp。然后将此新节点插入列表中。
主循环的下一次迭代然后用值填充addLocation()值，locationNode在列表中插入另一个全新的{{1}}。因此，第一个数据集不会存储在列表中，每次迭代都会通过插入未初始化的新节点而结束。
正如您所看到的那样，使用全局变量可能会导致混乱的情况，如果您将节点作为参数传递给函数，则代码肯定会变得更加清晰。