我正在进行一项相当冗长的任务，目前有一个致命的问题。我无法正确地实现节点访问存储在指针中的链表中存储的数据。
起初我收到了分段错误，但经过一些研究，例如this和this，我能够清除它。现在我已经修复了分段错误，我的代码甚至都不会编译！
我已经“调试”调试到我知道问题存在于我的Cache.h文件中，特别是在我的addElement函数中，当我尝试设置新节点p时等于某个数组值的起始节点。试图明确评论。
因为我的数组是一个链表的数组，它本质上是一个指针数组。类型声明为node *。我觉得p应该是指向指针的指针，因为它不是任何列表的一部分，需要通过数组访问数据。我已经尝试了大约一百万个指针组合和指针指针，但是没有什么能让我再次编译。我已经完成了所有我知道如何做的调试，所以我转向你。
我将发布以下代码。 commands.in基本上包含我将使用的文件的名称。 A.data是我正在对其进行操作的数据的文件（min为ex）。 Process.cpp包含我的主要功能，以及基本操作，而Cache.h实际上只是存在这个指针。
由于问题肯定存在于Cache.h中，我将首先发布，其他一切都要遵循。同样，错误位置应该是显而易见的。希望我对指针的理解和一个简单的解决方案有些错误。
谢谢！
Cache.h`
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
//CLASS TO STORE SIMPLE "CACHE"
class Cache
{
private:
struct node
{
double val;
string cacheName;
string cacheOp;
node * next;
};
node * cacheArr[26];
public:
//CONSTRUCTOR, SET VALUES OF cacheArr TO NULL
Cache()
{
for (int i = 0; i < 26; i++)
{
cacheArr[i] = new node;
}
}
//ADD AN ELEMENT TO CACHE
void addElement (string file, string op, double value)
{
node** p;
char ch = file[0];
//convert
int alphaNum = (int)(ch - 'A');
cout << "\nALPHA NUM = " << alphaNum << " -- ch = " << ch << endl;
cout << "TEST PRE";
/*
HERE LIES THE PROBLEM
vvvvvvvvvvvvvvvvvvvvv
*/
p* = cacheArr[alphaNum];
cout << "\nTEST";
if (p == NULL)
{
//no values starting with 'ch' have been used
//create new node
p->cacheName = file;
p->cacheOp = op;
p->val = value;
p->next = NULL;
return;
}
else if (p->next == NULL)
{
//list has one value, add to list if so
p = p->next;
p->cacheName = file;
p->cacheOp = op;
p->val = value;
p->next = NULL;
return;
}
//list has 2+ elements
//bring p to last element
while(p!=NULL)
{
p = p->next;
}
` //p is at end of list
p->cacheName = file;
p->cacheOp = op;
p->val = value;
p->next = NULL;
return;
}
//checks to see if file already in cache
bool checkCache(string file, string op)
{
char ch = file[0];
int numAlpha = (int)(ch - 'A' + 1);
node* p = cacheArr[numAlpha];
if(p == NULL)
{
return false;
}
while(p!=NULL)
{
if(p->cacheName == file && p->cacheOp == op)
{
return true;
}
p = p->next;
}
return false;
}
//RETURNS VALUE OF CACHE
double getVal(string file, string op)
{
char ch = file[0];
int numAlpha = (int)(ch - 'A' + 1);
node * p = cacheArr[numAlpha];
while (p!=NULL)
{
if(p->cacheName == file && p->cacheOp == op)
{
return p->val;
}
p = p->next;
}
return 0;
}
};
//END OF CLASS
Process.cpp：
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <ctime>
#include "Cache.h"
using namespace std;
//PROTOTYPE
double Avg(string fileName);
int Min(string fileName);
int Max(string filename);
double Med(string filename);
int main(){
//VARIABLES
int numFile;
string fileName;
string opName;
fstream fileObj;
double result;
ofstream resultFile;
Cache cacheObj;
bool inCache;
double elapsed_secs;
//OPEN FILES. READ FROM fileObj, WRITE TO resultFile
resultFile.open("results.out");
cout << "\n\n\n\n\n\n" << endl;
fileObj.open("commands.in");
fileObj >> numFile;
//ITERATE THROUGH FILES IN commands.in
for (int i = 0; i < numFile; i++){
fileObj >> fileName;
fileObj >> opName;
//CHECK IF IN CACHE
inCache = cacheObj.checkCache(fileName, opName);
if (inCache==false)
{
//DO AVG OP
if (opName == "Avg")
{
cout << "\n\nAvg file found. Filename = " << fileName<<endl;
clock_t begin = clock();
result = Avg(fileName);
cout << "test";
clock_t end = clock();
cacheObj.addElement(fileName, opName, result);
elapsed_secs = double(end - begin) / CLOCKS_PER_SEC;
cout << "Time for OP : " << elapsed_secs << endl;
cout << "result = " << result;
resultFile << fileName << " " << opName << ": " << result << " in " << elapsed_secs << " seconds" << endl;
}
//DO MIN OP
if (opName == "Min")
{
cout <<"\n\nMin file found. Filename = " << fileName << endl;
clock_t begin = clock();
result = Min(fileName);
clock_t end = clock();
cacheObj.addElement(fileName, opName, result);
elapsed_secs = double(end - begin) / CLOCKS_PER_SEC;
cout << "Time for OP : " << elapsed_secs << endl;
cout << "result = " << result;
resultFile << fileName << " " << opName << ": " << result << " in " << elapsed_secs << " seconds" << endl;
}
//DO MAX OP
if (opName == "Max")
{
cout <<"\n\nMax file found. Filename = " << fileName << endl;
clock_t begin = clock();
result = Max(fileName);
clock_t end = clock();
cacheObj.addElement(fileName, opName, result);
elapsed_secs = double(end - begin) / CLOCKS_PER_SEC;
cout << "Time for OP : " << elapsed_secs << endl;
cout << "result = " << result;
resultFile << fileName << " " << opName << ": " << result << " in " << elapsed_secs << " seconds" << endl;
}
//DO MED OP
if (opName == "Med")
{
cout << "\n\nMed file found. Filename = " << fileName << endl;
clock_t begin = clock();
result = Med(fileName);
clock_t end = clock();
cacheObj.addElement(fileName, opName, result);
elapsed_secs = double(end - begin) / CLOCKS_PER_SEC;
cout << "Time for OP : " << elapsed_secs << endl;
cout << "result = " << result;
resultFile << fileName << " " << opName << ": " << result << " in " << elapsed_secs << " seconds" << endl;
}
}else if(inCache == true)
{
clock_t begin = clock();
result = cacheObj.getVal(fileName, opName);
clock_t end = clock();
elapsed_secs = double(end-begin) / CLOCKS_PER_SEC;
cout << "Time for OP: " << elapsed_secs << endl;
resultFile << fileName << " " << opName << ": " << result << " in " << elapsed_secs << " seconds " << endl;
}
//END OF FOR LOOP
}
//END OF MAIN
return 0;
}
//COMPUTE AVG AS DOUBLE, RETURN
double Avg(string filename)
{
fstream file;
string name = filename + ".data";
file.open(name.c_str());
if (file.fail())
{
cout << "The file was not found" << endl;
return 0;
}
int count = 0;
double allNum = 0;
double current;
double result;
while(file)
{
file >> current;
allNum += current;
count++;
}
//WHY IS IT ADDING THE FINAL NUMBER TWICE?!
//THIS PART OF THE CODE IS BROKEN
result = allNum / count-1;
return result;
}
//COMPUTE THE MIN AS INT
int Min(string filename)
{
fstream file;
string name = filename + ".data";
file.open(name.c_str());
if (file.fail())
{
cout << "The file was not found" << endl;
return 0;
}
int min;
int test;
file >> min;
while (file)
{
file >> test;
if (test < min)
min = test;
}
return min;
}
//COMPUTE MAX AS INT
int Max(string filename)
{
fstream file;
string name = filename + ".data";
file.open(name.c_str());
if (file.fail())
{
cout << "The file was not found" << endl;
return 0;
}
int max = 0;
int test;
file >> max;
while (file)
{
file >> test;
if (test > max)
max = test;
}
return max;
}
//COMPUTE THE MED
double Med(string filename){
fstream file;
string name = filename + ".data";
file.open(name.c_str());
if (file.fail())
{
cout << "The file was not found" << endl;
return 0;
}
double val;
vector<double> medVect;
int count = 0;
//store file in vector
while(file)
{
file >> val;
medVect.push_back(val);
count++;
}
//sort the vector
double temp;
int vSize = medVect.size();
for (int i = 0; i < vSize; i++)
{
for (int j = 0; j < vSize; j++)
{
if (medVect.at(i) > medVect.at(j))
{
temp = medVect.at(i);
medVect.at(i) = medVect.at(j);
medVect.at(j) = temp;
}
}
}
//find the median for:
//odd values
if (vSize %2 == 1)
{
int mid = vSize / 2;
return medVect.at(mid+1);
}
int mid = vSize / 2;
double mid1 = medVect.at(mid);
double mid2 = medVect.at(mid+1);
double result = (mid1 + mid2) / 2;
return result;
//SAME THING, CODE READS LAST LINE OF FILE TWICE...NEED TO FIX
}
Commands.in
6
A Min
B Max
C Avg
A2 Max
B Max
ABC Med
A.Data`
20
20
30
30
40
40
`
忘了，我得到的错误代码。
[dilleyj@cs1 HW6]$ g++ -Wall -o process Process.cpp
In file included from Process.cpp:6:0:
Cache.h: In member function ‘void Cache::addElement(std::string, std::string, double)’:
Cache.h:59:7: error: expected primary-expression before ‘=’ token
p* = cacheArr[alphaNum];
^
Cache.h:67:8: error: request for member ‘cacheName’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->cacheName = file;
^
Cache.h:68:8: error: request for member ‘cacheOp’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->cacheOp = op;
^
Cache.h:69:8: error: request for member ‘val’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->val = value;
^
Cache.h:70:8: error: request for member ‘next’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->next = NULL;
^
Cache.h:73:16: error: request for member ‘next’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
else if (p->next == NULL)
^
Cache.h:76:14: error: request for member ‘next’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p = p->next;
^
Cache.h:77:9: error: request for member ‘cacheName’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->cacheName = file;
^
Cache.h:78:9: error: request for member ‘cacheOp’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->cacheOp = op;
^
Cache.h:79:9: error: request for member ‘val’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->val = value;
^
Cache.h:80:9: error: request for member ‘next’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->next = NULL;
^
Cache.h:88:13: error: request for member ‘next’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p = p->next;
^
Cache.h:93:8: error: request for member ‘cacheName’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->cacheName = file;
^
Cache.h:94:8: error: request for member ‘cacheOp’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->cacheOp = op;
^
Cache.h:95:8: error: request for member ‘val’ in ‘* p’, which is of pointer type ‘Cache::node*’ (maybe you meant to use ‘->’ ?)
p->val = value;
^
`
答案 0 :(得分：1)
至少有两个问题。
p* = cacheArr[alphaNum];应为*p = cacheArr[alphaNum];
然后，在同一个函数中，p->应为(*p)->，因为p是指向指针的指针。