Question

我创建了一个DirList类来获取特定目录中的所有目录，文件列表。下面是DirList代码。

getDerivedStateFromProps(nextProps, prevState) {
    console.log("Hello is anyone there?");
    console.log(nextProps);
    console.log(prevState);
    //Never called - supposed to update when new props received
}


const mapStateToProps = state => {
        const { ha, foo, bar } = state.groove;
        const { user, authorization } = state.auth;
        return {
            ha,
            foo,
            bar,
            user,
            authorization, //this is the ever so special token i need
        };
};

export default connect(mapStateToProps, { unrelatedFunctionName })(ComponentIWantToReRender);

DirList类使用如下

class DirList {
private:
    std::string dir_path_;
    int type_;
    DIR *dir_;

public:
    DirList(std::string dir_path);
    DirList(std::string dir_path, int type);
    ~DirList();

    std::string GetNext();
};

DirList::DirList(std::string dir_path) {
    DirList(dir_path, 0);
}

DirList::DirList(std::string dir_path, int type) {
    dir_path_ = dir_path;
    type_ = type;
    dir_ = opendir(dir_path_.c_str());

    if (dir_ == NULL)
        std::cout << "DirList - opendir error - " << dir_path_;

    Logger(Logger::kError) << "path " << dir_path_ << " type " << type_;
    Logger(Logger::kError) << "address " << (uint64_t)this;
}

DirList::~DirList() {
    if (closedir(dir_) != 0)
        std::cout << "DirList - close error - " << dir_path_;
}

std::string DirList::GetNext() {
    Logger(Logger::kError) << "path " << dir_path_ << " type " << type_;
    Logger(Logger::kError) << "address " << (uint64_t)this;

    if (dir_ == NULL) {
        std::cout << "DirList - opendir error - " << dir_path_;
        return "";
    }

    dirent *dirent;
    if(type_ == 0){
        while ((dirent = readdir(dir_)) != NULL) {
            // Jump current and upper dir
            if (dirent->d_name[0] == '.')
                continue;
            else
                break;
        }
    }
    else{
        while ((dirent = readdir(dir_)) != NULL) {
            // Jump current and upper dir
            if ((dirent->d_name[0] == '.') || (dirent->d_type != type_))
                continue;
            else
                break;
        }
    }

    if (dirent == NULL)
        return "";

    return dirent->d_name;
}

当构造函数中的此地址和GetNext方法中的此地址时，DirList在某些代码中运行良好。但是当这个地址不同时，DirList并没有在某些代码中运行...所以dir_path_，type_有错误的值。

我不明白为什么实例的地址被改变了。我没有解决操作只使用new来分配内存。

My Devel Env是Ubuntu 17.10 64bit and clang - ++ 3.8。但我尝试了Ubuntu 16.04 64bit，clang - ++ 4.0。 clang - ++ 5.0 ......但同样的问题也出现了。

感谢

Answer 1

我找到了原因

DirList::DirList(std::string dir_path) { DirList(dir_path, 0); }

＆＃39; DirList（dir_path，0）＆＃39;不是init这个实例。它只会使临时实例。

解决这个问题 DirList::DirList(std::string dir_path) : DirList(dir_path, 0) {}

C ++实例的地址更改

1 个答案: