向量成员已重置且无法访问 [英] A vector member is reset and unaccessible

问题描述

我有两个项目，一个基本客户端和一个动态库. 这是客户端中发生的事情:

I have two projects, one basic client and a dynamic library. Here's what happens in the client:

int main()
{
    Scrutinizer scru;
    scru.Scrutinize();
    return 0;
}

在DLL中，Scrutinizer类就是这样的(__ declspec(dllexport)，为了清晰起见，省略了此类)

In the DLL, The Scrutinizer class is as such (__declspec(dllexport) and such omitted for Clarity)

标题

class ProcessesGenerator;

    class Scrutinizer
    {
    public:
    Scrutinizer();
    ~Scrutinizer();
    ProcessesGenerator *ProcGenerator
    void Scrutinize();
};

ProcessesGenerator的前向声明对我来说是强制性"，以避免某种形式的循环引用.

The forward declaration of ProcessesGenerator was 'mandatory' for me to avoid some kind of circular reference.

.cpp文件中的构造函数

这是我如何初始化它:

Scrutinizer::Scrutinizer()
{
    ProcGenerator = &ProcessesGenerator();
}

有关此ProcessesGenerator类的更多信息:

标题

class ProcessesGenerator
{

public:
    ProcessesGenerator();
    ~ProcessesGenerator();
    WinFinder winFinder;
    std::vector<std::string> fooCollec;

    void GenerateProcesses();
};

ProcessesGenerator.cpp

构造函数:

ProcessesGenerator::ProcessesGenerator()
{
    //winFinder = WinFinder();//problem will be the same with or without this line
    fooCollec = std::vector<std::string>{"one", "two", "three"};
}

构造函数中的断点表明，向量已使用选定的值进行了初始化.

A breakpoint in the constructor shows that the vector is initialized with the chosen values.

问题功能:

void ProcessesGenerator::GenerateProcesses() {
    std::string foo = "bar";
    fooCollec = std::vector<std::string>{};//read access violation
    fooCollec.push_back(foo);//read access violation
    winFinder.SomeVector= std::vector<std::string>{};//read access violation
}

在那里，我可以看到vector的大小被重置为0.任何尝试重新初始化它或推入元素的操作都会导致读取访问冲突.与它的WinFinder成员的vecotr成员相同.我想这个缺陷很明显，但是我真的不明白，

Once there, I Can see that the size of vector is reset to 0. Any attempt to re-initialize it, or to push an element results in read access violation .Same with the vecotr member of its WinFinder member. I guess the flaw is obvious, but I really don't get it,

谢谢！

推荐答案

您的问题出在

Scrutinizer::Scrutinizer()
{
    ProcGenerator = &ProcessesGenerator();
}

您正在做的是获取一个临时对象的地址.该对象将被销毁，并在该行的末尾，您将获得一个指向有效对象的指针.

What you are doing is taking the address of a temporary object. That object will be destroyed and the end of that line and you will be left with a pointer that doesn't point to a valid object.

解决此问题的旧方法是使用

The old way to fix it would be to use

Scrutinizer::Scrutinizer()
{
    ProcGenerator = new ProcessesGenerator();
}

但是现在您必须实现复制构造函数，复制赋值运算符和析构函数.由于您使用的是现代编译器，因此可以代替的是将ProcGenerator设置为std:unique_ptr<ProcessesGenerator>，然后将Scrutinizer()变为

But now you have to implement the copy constructor, copy assignment operator, and the destructor. Since you have a modern compiler what you can do instead is make ProcGenerator a std:unique_ptr<ProcessesGenerator> and then Scrutinizer() becomes

Scrutinizer::Scrutinizer() : ProcGenerator(make_unique<ProcessesGenerator>()) {}

---

我还想补充一点，&ProcessesGenerator();甚至不应该编译.不幸的是，MSVS具有非标准扩展名，因此可以对其进行编译.您可以打开/Za编译器选项(强制ANSI兼容性)，然后会出现类似错误

---

I would also like to add that &ProcessesGenerator(); should not even compile. Unfortunately MSVS has a non-standard extension that allows this to compile. You can turn on the /Za compiler option (enforce ANSI compatibility) and then you should get an error like

错误C2102:&"需要左值

error C2102: '&' requires l-value

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