C 中簡單代碼中的奇怪語法錯誤

這段代碼中有一個奇怪的語法錯誤。我不明白它或任何錯誤。

#pragma once
#include <iostream>
class Tree {
public:
    Node* root;
    void InputTree() {
        int n, father;
        int nd;
        int child;
        char dir;
        std::cin >> n;
        int** tree = new int* [n];
        for (int i = 0; i < n; i  ) {
            std::cin >> nd;
            tree[i] = new int[3];
            tree[i][0] = nd;
            tree[i][1] = -1;
            tree[i][2] = -1;
        }

        for (int i = 0; i < n - 1; i  ) {
            std::cin >> father >> child >> dir;
            if (dir == 'L')
                tree[father][1] = child;
            else
                tree[father][2] = child;
        }
        Initialize(tree, 0);
    }
private:
    void Initialize(int** tree, int headIndex) {
        if (headIndex != -1) {
            root->value = tree[headIndex][0];
            root->right_tree->Initialize(tree, tree[headIndex][2]);
            root->left_tree->Initialize(tree, tree[headIndex][1]);
        }
    }
};
class Node {
public:
    int value;
    Tree* left_tree;
    Tree* right_tree;
};

這是 Visual Studio 的構建輸出：

Build started...
1>------ Build started: Project: CppMainProject, Configuration: Debug Win32 ------
1>CppMainProject.cpp
1>tstream.h(5,6): error C2143: syntax error: missing ';' before '*'
1>tstream.h(5,6): error C4430: missing type specifier - int assumed. Note: C   does not support default-int
1>tstream.h(5,12): error C2238: unexpected token(s) preceding ';'
1>tstream.h(33,4): error C2065: 'root': undeclared identifier
1>tstream.h(34,4): error C2065: 'root': undeclared identifier
1>tstream.h(35,4): error C2065: 'root': undeclared identifier
1>Done building project "CppMainProject.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

uj5u.com熱心網友回復：

在諸如root->value = tree[headIndex][0];之Node類的行中，您在告訴編譯器該類是什么之前嘗試使用該類。您可以在類的完整定義之前將變數宣告為指向類的指標（但您需要類的前向宣告才能這樣做），但在提供完整的類定義之后才能取消參考此類指標。

在你的代碼，你可以定義移動Node類之前的Tree類; 但是，由于使用Tree指標，您必須提供一個Tree作為類的前向宣告。

#pragma once
#include <iostream>

class Tree; // Forward declaration that this is a class...

class Node {
public:
    int value;
    Tree* left_tree; // ... so we can now declare pointers to "Tree"
    Tree* right_tree;
};

class Tree {
public:
    Node* root; // We can declare a pointer 
    void InputTree()
    {
    // ... and then the rest of your code as is ...

一些值得一讀：我什么時候可以使用前向宣告？

uj5u.com熱心網友回復：

Node宣告時仍未定義root。嘗試在 Tree 類中移動 Node Class，我建議您將其更改為 struct 如下：

#pragma once
#include <iostream>
class Tree {
public:

    void InputTree() {
        int n, father;
        int nd;
        int child;
        char dir;
        std::cin >> n;
        int** tree = new int* [n];
        for (int i = 0; i < n; i  ) {
            std::cin >> nd;
            tree[i] = new int[3];
            tree[i][0] = nd;
            tree[i][1] = -1;
            tree[i][2] = -1;
        }

        for (int i = 0; i < n - 1; i  ) {
            std::cin >> father >> child >> dir;
            if (dir == 'L')
                tree[father][1] = child;
            else
                tree[father][2] = child;
        }
        Initialize(tree, 0);
    }
private:
    struct Node {
        int value;
        Tree* left_tree;
        Tree* right_tree;
    };
    Node* root;
    void Initialize(int** tree, int headIndex) {
        if (headIndex != -1) {
            root->value = tree[headIndex][0];
            root->right_tree->Initialize(tree, tree[headIndex][2]);
            root->left_tree->Initialize(tree, tree[headIndex][1]);
        }
    }
};

uj5u.com熱心網友回復：

如果你希望它都在一個檔案中，向前宣告Node并移動 . 定義Tree::Initialize(...)之后的定義Node。或者只是向前宣告Node并使用典型的 .h 檔案 / .cpp 檔案拆分。

單檔案版本是這樣的：

class Node;  // <= this is a forward declaration...

class Tree {
public:
    Node* root;
    void InputTree() {
        // ....
    }
private:
    void Initialize(int** tree, int headIndex);
};

class Node {
public:
    int value;
    Tree* left_tree;
    Tree* right_tree;
};

void Tree::Initialize(int** tree, int headIndex)
{
    // ...
}

標籤：C 视觉工作室

上一篇：C讀取訪問沖突-指標

下一篇：“setup.h”wxwidget的問題-“無法打開檔案”