[英]Allocating memory for class in C++
这是我的课:
using namespace std;
Class Book {
public:
Book();
Book(vector<string>*, string, int);
Book(const Book&);
~Book();
Book& operator=(const Book&);
void update(vector<string>*);
void update(string);
void update(int);
int getYear() const{
return year;
};
string getTitle() const{
return title;
};
bool operator==(const Book&);
bool operator!=(const Book&);
friend std::ostream& operator<<(std::ostream&, const Book&);
void getAuthors();
private:
vector<string>* authors;
string title;
int year;
};
#endif /* BOOK_H */
这是它的来源:
#include "Book.h"
using namespace std;
Book::Book():year(0), title(NULL), authors(NULL){}
Book::Book(vector<string>* bookauthors,string booktitle, int bookyear ){
authors = bookauthors;
title = booktitle;
year = bookyear;
}
Book::Book(const Book& aBook){
authors = aBook.authors;
title = aBook.title;
year = aBook.year;
}
Book::~Book(){
delete authors;
delete &title;
delete &year;
}
bool Book::operator==(const Book &aBook){
if(getYear() == aBook.getYear() && getTitle() == aBook.getTitle())
return true;
else return false;
}
bool Book::operator != (const Book &aBook){
if(getYear() != aBook.getYear() && getTitle() != aBook.getTitle())
return true;
else return false;
}
Book& Book::operator =(const Book& rhs){
if(this != &rhs){
authors = rhs.authors;
title = rhs.title;
year = rhs.year;
}
return *this;
}
void Book::update(int newyear){
year = newyear;
}
void Book::update(string newtitle){
title = newtitle;
}
void Book::update(vector<string>* newauthors){
authors = newauthors;
}
std::ostream& operator <<(std::ostream& os, const Book& b){
os<<b.getTitle()<<", "<<b.getYear();
return os;
}
这是它运行的主要文件:
#include "Book.h"
#include <iostream>
#include <limits.h>
//This is the test funcion posted on the class website
using namespace std;
int main(){
//testing constructor
vector<string> authors;
authors.push_back("Ritchie");
authors.push_back("Kernighan");
Book a(&authors, "C", 1990);
authors.push_back("Whatever");
cout << "Book a is: " << a << endl;
cout << "Expected: (C, 1990, Ritchie & Kernighan)" << endl;
//testing copy constructor
Book b(a);
a.update(&authors);
cout << "Book b is: " << b << endl;
cout << "Expected: (C, 1990, Ritchie & Kernighan)" << endl;
//testing constructor
vector<string> authors2;
authors2.push_back("Crockford");
Book c(&authors2, "JavaScript", 2008);
cout << "Book c is: " << c << endl;
cout << "Expected: (JavaScipt, 2008, Crockford)" << endl;
//testing assignment operator
authors2.push_back("whatever");
a=c;
cout << "Book a is changed to: " << a << endl;
cout << "Expected: (JavaScipt, 2008, Crockford)" << endl;
for(int i=0; i < 200000000; i++)
b=c;
cout << "Book b is changed to: " << b << endl;
cout << "Expected: (JavaScipt, 2008, Crockford)" << endl;
}
运行它时,我一直得到这个:
bookclass(58316)malloc: *对象0x7fff522d78b0错误:未分配要释放的指针*在malloc_error_break中设置一个断点以进行调试
我是C ++的新手,所以不确定如何分配内存。 我尝试使用malloc
,但没有用。
成员位于对象内部,即,它们的内存是通过Book
对象分配的,既不需要也不需要显式delete
内存。 基本上,您需要使用new
与delete
调用来匹配您的显式分配,但是您无需释放未明确分配的内容。
也就是说,当您尝试delete title
或delete year
时,会出现错误。 当尝试delete authors
时,也可能发生这种情况,具体取决于authors
来自何处。 通常,您不想delete
尚未分配的对象。 您的Book
类可能不合理地拥有了authors
载体的所有权。
这可能是学习使用Valgrind的好时机,它将为您提供丰富的调试工具,以解决此类错误。
在析构函数中,您正在通过指针销毁标题和年份。 您实际上并不需要这样做,因为它们是静态分配的(即您没有使用new创建它们),因此它抱怨您试图删除不是动态创建的内容。
另外,您将删除std::vector
,它可以引用另一个类中包含的相同std::vector
。 由于可能有两个包含相同引用的类,因此您需要找到一种更聪明的方式来删除该引用,从而避免调用double free。
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