C++ C++;从main()通过类函数传递指针
我知道指针是经常被讨论的东西。为了解决这个问题,我做了很多研究,但一切都让我走到了死胡同 我有一个作业要求我创建一个记录单个测试分数的类。如果已记录测试分数,且新分数更高,则覆盖该分数。如果已记录,且新分数较低,则不执行任何操作。如果没有录制,请录制 以下是我到目前为止的情况:C++ C++;从main()通过类函数传递指针,c++,class,pointers,C++,Class,Pointers,我知道指针是经常被讨论的东西。为了解决这个问题,我做了很多研究,但一切都让我走到了死胡同 我有一个作业要求我创建一个记录单个测试分数的类。如果已记录测试分数,且新分数更高,则覆盖该分数。如果已记录,且新分数较低,则不执行任何操作。如果没有录制,请录制 以下是我到目前为止的情况: // CIS 235 exercise 7 #include <iostream> using namespace::std; // declare a class for recording
// CIS 235 exercise 7
#include <iostream>
using namespace::std;
// declare a class for recording a test score
// the data will be pointer to an integer, rather than an integer
//
// - this exercise is designed to show how to work with pointer memory
// - of course, we would NOT normally use a pointer for just an integer
// - to illustrate the concepts, but keep the implementation simple,
// integer data was used. The general case would be object data,
// not integer data
class testScore
{
public:
// declare a default constructor - the pointer should be set to NULL
testScore();
// declare a function that returns a bool, indicating if the test has been taken
bool hasTestTaken();
// declare a function to record the test score, the parameter will be an integer
// use the following rules
// - if no test has been taken, allocate memory and record the score
// - if a test has been taken and the parameter is less than or equal to
// the score, do nothing
// - if the test has been taken and the parameter is higher than the score,
// - release the old memory
// - allocate new memory
// - record the score
void recordScore(int *myScore);
// declare a function to print the score to an ostream parameter
// if the test has not been taken, send an appropriate message to the ostream
// otherwise print the score
void printScore(ostream &out);
// declare the destructor
// be CAREFUL, you will need an if statement in your destructor
~testScore();
private:
// declare the data needed to implement the class
bool testTaken;
int *score;
};
// write the 5 member functions
testScore::testScore() : score(NULL)
{
// declare a default constructor - the pointer should be set to NULL
}
bool testScore::hasTestTaken()
{
// declare a function that returns a bool, indicating if the test has been taken
return testTaken;
}
void testScore::recordScore(int *myScore)
{
if(testTaken == false)
{
testTaken = true;
*score = *myScore;
}
else if(testTaken == true && *myScore > *score)
{
score = NULL;
delete score;
score = new int;
*score = *myScore;
}
}
void testScore::printScore(ostream& out)
{
// declare a function to print the score to an ostream parameter
// if the test has not been taken, send an appropriate message to the ostream
// otherwise print the score
if(testTaken)
{
out << *score << endl;
}
else
out << "The test has not been taken!" << endl;
}
testScore::~testScore()
{
// declare the destructor
// be CAREFUL, you will need an if statement in your destructor
if(score != NULL)
{
score = NULL;
delete score;
}
else
delete score;
}
// test the class member functions
// - declare an object, but do NOT record a score for the object
// - declare a second object and record the scores of 83, 78, 92
// use appropriate member print functions to verify your code
//int abc = 83;
int abc = 0;
int main()
{
// int abc = 0;
// int * score2;
// myTestScore = new int;
// *myTestScore = 83;
testScore firstScore;
firstScore.printScore(cout);
testScore secondScore;
// secondScore.recordScore(&abc);
secondScore.recordScore(&abc);
// secondScore.printScore(cout);
// *myTestScore = 78;
// secondScore.recordScore(myTestScore);
// secondScore.printScore(cout);
// *myTestScore = 92;
// secondScore.recordScore(myTestScore);
// secondScore.printScore(cout);
system("PAUSE");
return 0;
}
我不知道为什么T.T
我也尝试过:
宣布
int *myTestScore;
myTestScore = new int;
*myTestScore = 83;
在main()内部,但在其他内容之前,通过以下方式将myTestScore传递给recordScore:
&myTestScore
编译错误:调用“testScore::recordScore(int**)”时没有匹配的函数;
在secondScore.recordScore行
*myTestScore
myTestScore
编译错误:从“int”到“int*”的转换无效
在secondScore.recordScore行
*myTestScore
myTestScore
没有编译错误,在将任何内容输出到控制台之前运行时崩溃
我试着声明:
int *myTestScore = 83;
在int main()的内部
编译错误:从“int”到“int*”的转换无效
在int*myTestScore=83行上
我还尝试了各种方法,将recordScore更改为使用&'s和*,以及两者都不使用,以及两者的不同组合
我现在没有想法去尝试,即使在研究之后,我也不能想出任何东西。我试着问我的教授(一个星期了,在线课程),打电话给她,发电子邮件给她,但她没有回答我的任何问题,甚至没有要求开会
我觉得这里有一些简单的东西我没有掌握,我真的很感谢任何人能给我帮助来解决这个问题
非常感谢您抽出时间
变化:
testScore::testScore() : score(NULL), testTaken(false) // didnt change because instructor instructions, but did move testTaken up cause that is where it should be
{
// declare a default constructor - the pointer should be set to NULL
}
void testScore::recordScore(int myScore)
{
if(testTaken == false)
{
testTaken = true;
score = &myScore;
cout << *score << endl; //this prints correctly, 0
}
else if(testTaken == true && myScore > *score)
{
//removed the score = NULL to avoid a memory leak (I think this is correct now?)
delete score;
score = new int;
score = &myScore;
}
}
void testScore::printScore(ostream& out)//no changes, just easier to access to you dont have to keep scrolling up
{
// declare a function to print the score to an ostream parameter
// if the test has not been taken, send an appropriate message to the ostream
// otherwise print the score
if(testTaken)
{
out << *score << endl; //outputs incorrect 4469696
}
else
out << "The test has not been taken!" << endl;
}
int main()
{
int abc = 0;
testScore firstScore;
firstScore.printScore(cout);
testScore secondScore;
secondScore.recordScore(abc);
secondScore.printScore(cout);
system("PAUSE");
return 0;
}
testScore::testScore():score(NULL),testtake(false)//没有因为讲师的指示而更改,但确实移动了testtake,因为它应该在那里
{
//声明默认构造函数-指针应设置为NULL
}
void testScore::recordScore(intmyscore)
{
if(testtake==false)
{
testtake=true;
分数=&myScore;
cout主要问题是,在默认构造函数中,您将NULL
赋值给score,因此指针将指向无效内存。因此,当您调用recordStore时,当程序到达此指令时:
*score = *myScore;
它会导致分段错误,当您试图覆盖程序未使用的内存部分时会发生此错误
程序不会在printScore中崩溃,因为读取无效指针不是错误,但会读取垃圾数据
编辑:根据您的分配,如果未进行测试,则必须在recordStore中分配指针,因此在recordStore中,更改此部分:
if(testTaken == false)
{
testTaken = true;
*score = *myScore;
}
为此:
if(testTaken == false)
{
score = new int;
testTaken = true;
*score = *myScore;
}
另外,在执行delete
部分时,首先将指针指定为NULL,然后将其删除;因此程序将尝试删除NULL
指针(这不会导致错误),并且用于分数的内存未释放,导致内存泄漏声明一个函数来记录测试分数,参数将是一个整数。您声明它将指针指向一个整数。阅读您的问题,我建议您停下来,深呼吸,然后重新阅读指针上的材料。如果您在t*myScore=83;
需要问一下,这意味着你需要学习更多。Merr,一开始她说://声明一个用于记录考试分数的类//数据将指向一个整数,而不是一个整数,这是类的要求,而不是recordSCore
的签名。好吧……那么,如果我这样做的话将其改为int,并切换一些内容,我可以让它正确记录分数,但打印功能中断…上载新代码?啊,我没有意识到关于删除的事情。谢谢!关于分数的事情…我的导师希望它设置为NULL,因此我必须:(-但是你提供的关于指针对null无效的信息是有用的,谢谢你!但是,在recordScore下,当它不在那里时,它会正确打印…当它到达printScore时,它会在过程中以某种方式变回null,或者可能只是垃圾,或者其他东西,我不能完全确定。如果你谈到更改部分,当您通过值而不是指针传递int时,将传递abc的副本。该副本将在函数结束后被删除。因此,稍后它将成为垃圾值。