C++ 虚拟类中如何利用字符串指针避免内存泄漏
我正在编写一个基类,其中包含一个指向字符串的指针,现在我正在尝试使用赋值运算符编写一个派生类,用新值替换它。对于这个特定的项目,我需要将字符串存储为指针 起初,我尝试使用C++ 虚拟类中如何利用字符串指针避免内存泄漏,c++,class,pointers,overloading,C++,Class,Pointers,Overloading,我正在编写一个基类,其中包含一个指向字符串的指针,现在我正在尝试使用赋值运算符编写一个派生类,用新值替换它。对于这个特定的项目,我需要将字符串存储为指针 起初,我尝试使用new,但编译失败 kolo& operator=(const kolo& ref){ if(this!=&ref){ delete kolor; kolor=new string(ref.kolor); r=ref.r; } return *this; } 我已将其
new
,但编译失败
kolo& operator=(const kolo& ref){
if(this!=&ref){
delete kolor;
kolor=new string(ref.kolor);
r=ref.r;
}
return *this;
}
我已将其更改为使用赋值运算符,该运算符已成功编译。然而,valgrind现在报告内存泄漏以及其他问题
kolo& operator=(const kolo& ref){
if(this!=&ref){
delete kolor;
*kolor=*ref.kolor;
r=ref.r;
}
return *this;
}
为什么valgrind报告我的赋值运算符内存泄漏?
我的完整代码(波兰语):
class-figura{
受保护的:
字符串*kolor;
公众:
figura():kolor(新字符串(“nic”){}
图A(常量字符串和a1):kolor(新字符串(a1)){}
虚拟双极()常数=0;
虚空wypisz(ostream&out)常数{
out去掉指针,这样就有了规则0:)
class-figura
{
受保护的:
科洛尔线;
公众:
图a():kolor(“nic”){}
/*显式*/figura(常量字符串&s):kolor(s){
virtual~figura()=默认值;
虚拟双极()常数=0;
virtualvoid wypisz(ostream&out)const{out表示,如果您实现析构函数、复制赋值或复制构造函数中的任何一个,您需要实现这三个。您已经为kolo
完成了此操作,但没有为图a
在代码中的某个地方,kolo
正在被复制构造(例如,在向量内部),并使用默认版本的figurea
s copy constructor。这将简单地复制指针。现在,原始字符串已丢失,导致泄漏。新字符串由两个不同的对象指向,因此将被销毁两次。第二次销毁是导致无效读取和删除的原因
有多种方法可以实现复制赋值和复制构造函数,而不必重复代码
我还希望,因为figurea
实际上是一个上面有kolor
的类,所以figurea
的复制分配应该负责,而不是kolor
的复制分配。这样,如果您从figurea
派生另一个类,您就不需要重新实现kolor
复制
听起来你需要使用原始指针,但一般来说,写内存管理的最好方法是不要写内存管理。直接使用字符串,以及字符串的内置内存管理,会让事情变得更简单。或者,使用智能指针,比如shared\ptr
可以让你完成cop自动删除和自动删除。< /P> <代码>新的字符串< /代码>?是否真的需要字符串指针而不是“代码> STD::String < /Cord>”?是否考虑异常安全?包含错误的问题?您将进入函数的第一个版本。但是,我怀疑问题在于,您在尝试复制它时没有取消引用ref.kolor
:新字符串(*ref.kolor);
。第二个版本会导致未定义的行为,因为您访问已删除的指针。@Spectra在运算符的第一个实现中,您应该使用kolor=new string(*ref.kolor);@vladFrommosco仍然在Valgrindt中泄漏内存。非常感谢您,这在类figura中起作用(我添加了复制构造函数)!
class figura {
protected:
string *kolor;
public:
figura() : kolor(new string("nic")) {}
figura(const string& a1) : kolor(new string(a1)) {}
virtual double pole() const = 0;
virtual void wypisz(ostream& out) const {
out<<*kolor;
}
friend ostream& operator<<(ostream& out,const figura& r);
virtual ~figura() { delete kolor; }
};
class kolo: public figura {
protected:
unsigned r;
public:
kolo(): figura(), r(0) {}
kolo(const string& a1, const unsigned a2) :figura(a1), r(a2) {}
kolo(const kolo& ref) : figura(ref), r(ref.r) {}
kolo& operator=(const kolo& ref) {
if(this!=&ref) {
delete kolor;
*kolor=*ref.kolor;
r=ref.r;
}
return *this;
}
double pole()const{
return 3.14*r*r;
}
void wypisz(ostream& out)const{
out<<"Kolor: "<<*kolor<<" "<<"Skladowe: "<<r<<endl;
}
friend ostream& operator<<(ostream& out,const kolo& r);
};
==1774== Invalid read of size 8
==1774== at 0x49ABE34: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.28)
==1774== by 0x10AB7F: figura::~figura() (test.cpp:14)
==1774== by 0x10B155: kolo::~kolo() (test.cpp:20)
==1774== by 0x10A7B4: main (test.cpp:84)
==1774== Address 0x4dc1c80 is 0 bytes inside a block of size 32 free'd
==1774== at 0x483C1CF: operator delete(void*, unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1774== by 0x10AB8C: figura::~figura() (test.cpp:14)
==1774== by 0x10B155: kolo::~kolo() (test.cpp:20)
==1774== by 0x10B175: kolo::~kolo() (test.cpp:20)
==1774== by 0x10A78B: main (test.cpp:102)
==1774== Block was alloc'd at
==1774== at 0x483AE63: operator new(unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1774== by 0x10AAD8: figura::figura(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (test.cpp:8)
==1774== by 0x10AC27: kolo::kolo(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned int) (test.cpp:25)
==1774== by 0x10A467: main (test.cpp:84)
==1774==
==1774== Invalid free() / delete / delete[] / realloc()
==1774== at 0x483C1CF: operator delete(void*, unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1774== by 0x10AB8C: figura::~figura() (test.cpp:14)
==1774== by 0x10B155: kolo::~kolo() (test.cpp:20)
==1774== by 0x10A7B4: main (test.cpp:84)
==1774== Address 0x4dc1c80 is 0 bytes inside a block of size 32 free'd
==1774== at 0x483C1CF: operator delete(void*, unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1774== by 0x10AB8C: figura::~figura() (test.cpp:14)
==1774== by 0x10B155: kolo::~kolo() (test.cpp:20)
==1774== by 0x10B175: kolo::~kolo() (test.cpp:20)
==1774== by 0x10A78B: main (test.cpp:102)
==1774== Block was alloc'd at
==1774== at 0x483AE63: operator new(unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1774== by 0x10AAD8: figura::figura(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (test.cpp:8)
==1774== by 0x10AC27: kolo::kolo(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned int) (test.cpp:25)
==1774== by 0x10A467: main (test.cpp:84)
==1774==
==1774==
==1774== HEAP SUMMARY:
==1774== in use at exit: 32 bytes in 1 blocks
==1774== total heap usage: 14 allocs, 14 frees, 74,088 bytes allocated
==1774==
==1774== 32 bytes in 1 blocks are definitely lost in loss record 1 of 1
==1774== at 0x483AE63: operator new(unsigned long) (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1774== by 0x10AA29: figura::figura() (test.cpp:7)
==1774== by 0x10ABE1: kolo::kolo() (test.cpp:24)
==1774== by 0x10A561: main (test.cpp:88)
==1774==
==1774== LEAK SUMMARY:
==1774== definitely lost: 32 bytes in 1 blocks
==1774== indirectly lost: 0 bytes in 0 blocks
==1774== possibly lost: 0 bytes in 0 blocks
==1774== still reachable: 0 bytes in 0 blocks
==1774== suppressed: 0 bytes in 0 blocks
==1774==
==1774== For lists of detected and suppressed errors, rerun with: -s
==1774== ERROR SUMMARY: 3 errors from 3 contexts (suppressed: 0 from 0)
class figura
{
protected:
string kolor;
public:
figura() : kolor("nic") {}
/*explicit*/ figura(const string& s) : kolor(s){}
virtual ~figura() = default;
virtual double pole()const = 0;
virtual void wypisz(ostream& out)const { out<< kolor; }
friend ostream& operator<<(ostream& out,const figura& r);
};
class kolo:public figura
{
protected:
unsigned r = 0;
public:
kolo() : figura(), r(0){}
kolo(const string& s,const unsigned r):figura(s), r(r){}
kolo(const kolo& ref) = default;
kolo& operator=(const kolo& ref) = default;
double pole()const override { return 3.14*r*r; }
void wypisz(ostream& out)const override {
std::out << "Kolor: " << kolor << " " << "Skladowe: " << r << std::endl;
}
friend ostream& operator<<(ostream& out,const kolo& r);
};