std::vector无sort成员编译错误及Shape类排序实现求助

Hey there! Let's break down the issues in your code and fix them step by step.

1. The immediate compile error: vector has no sort member function #

First off, that error happens because std::vector doesn’t have a built-in sort() method. Sorting standard containers like vector uses the standalone std::sort algorithm from the <algorithm> header. To fix this:

• Add #include <algorithm> to your top-level includes.
• Replace the line orderedList.sort(); with a call to std::sort, paired with a comparator that knows how to compare your Shape* pointers.

2. Fix operator< const correctness #

Your current operator< isn’t marked const, which means it can’t be called on const Shape objects. Since we’ll be dereferencing const Shape* pointers in our comparator, this would cause another compile error. Update the method to:

bool operator<(const Shape& s) const {
    return Precedes(s);
}

3. Fix the typeid portability issue (your ordering won’t work as-is) #

typeid(*this).name() returns a compiler-specific string. For example, in GCC, Triangle will show up as 7Triangle (the number is the length of the class name), so your strcmp checks against typeOrderTable will never match.

A reliable, portable fix is to add a virtual method to return the type name explicitly. Modify the Shape class:

class Shape {
public:
    virtual void Draw() const = 0;
    virtual bool Precedes(const Shape&) const;
    bool operator<(const Shape& s) const {
        return Precedes(s);
    }
    // Add this virtual method to return a human-readable type name
    virtual const char* GetTypeName() const = 0;
private:
    // Make this const char* to match string literals
    static const char* typeOrderTable[];
};

// Update the table to use const char* and nullptr instead of 0
const char* Shape::typeOrderTable[] = {"Rectangle","Square","Triangle", nullptr };

// Rewrite Precedes to use GetTypeName instead of typeid
bool Shape::Precedes(const Shape& s) const {
    const char* thisType = GetTypeName();
    const char* argType = s.GetTypeName();
    bool done = false;
    int thisOrd = -1;
    int argOrd = -1;
    for (int i=0; !done; i++) {
        const char* tableEntry = typeOrderTable[i];
        if (tableEntry != nullptr) {
            if (strcmp(tableEntry, thisType) == 0)
                thisOrd = i;
            if (strcmp(tableEntry, argType) == 0)
                argOrd = i;
            // Check if both types are found (use >=0 since indices start at 0)
            if ((argOrd >= 0) && (thisOrd >= 0))
                done = true;
        } else 
            done = true;
    }
    // Handle cases where a type isn't in the table (put unknown types last)
    if (thisOrd == -1) return false;
    if (argOrd == -1) return true;
    return thisOrd < argOrd;
}

Then override GetTypeName in each subclass:

class Square : public Shape {
public:
    virtual void Draw() const {
        std::cout << "Inside Draw of Square \n" ;
    }
    const char* GetTypeName() const override {
        return "Square";
    }
};

class Rectangle : public Shape {
public:
    virtual void Draw() const {
        std::cout << "Inside Draw of Rectangle \n" ;
    }
    const char* GetTypeName() const override {
        return "Rectangle";
    }
};

class Triangle : public Shape {
public:
    virtual void Draw() const {
        std::cout << "Inside Draw of Triangle \n" ;
    }
    const char* GetTypeName() const override {
        return "Triangle";
    }
};

4. Update the DrawAllShapes function #

With the fixes above, update your sorting logic to use std::sort and a lambda comparator that dereferences the pointers to use your operator<:

void DrawAllShapes(std::vector<Shape*>& list) {
    std::vector<Shape*> orderedList = list;
    // Sort using our custom comparison logic
    std::sort(orderedList.begin(), orderedList.end(), [](const Shape* a, const Shape* b) {
        return *a < *b;
    });
    std::vector<Shape*>::iterator it = orderedList.begin();
    for (;it!=orderedList.end(); ++it)
        (*it)->Draw();
}

5. Bonus: Fix memory leaks #

You’re allocating shapes with new but never deleting them, which causes memory leaks. Add cleanup in main():

int main() {
    std::vector<Shape*> vec;
    vec.push_back(new Triangle);
    vec.push_back(new Square);
    vec.push_back(new Rectangle);
    vec.push_back(new Square);
    DrawAllShapes(vec);
    
    // Clean up allocated memory
    for (Shape* s : vec) {
        delete s;
    }
    vec.clear();
    return 0;
}

Now your code will compile, sort shapes according to your typeOrderTable (Rectangle → Square → Triangle), draw them in that order, and clean up memory properly.

内容的提问来源于stack exchange，提问作者Invictus