Question

我正在尝试在2D矢量中搜索char，即'？'并用'x'替换它。

使用单个向量执行此任务没有问题但是仍然存在2D向量实现的问题，请参阅下面的代码。

#include <iostream>
#include <vector>
using namespace std;


int main()
{
        // An empty vector of vectors
        vector<vector<char> > v2d;

        // Create a vector with 5 elements
        vector<char> v2(5, '?');

        // Create a vector of 3 elements. 
        vector<vector<char> > v2d2(3, v2);

        // Print out the elements
        cout << "Before Vector Update" << endl;
        for (int i = 0; i < v2d2.size(); i++) {
            for (int j = 0; j < v2d2[i].size(); j++)
                cout << v2d2[i][j] << " ";
            cout << endl;
        }
        cout << "" << endl;

        /* Does not work as expected
        cout << "Vector Update" << endl;
        for (int i = 0; i < v2d2.size(); i++) {
            for (int j = 0; j < v2d2[i].size(); j++)
            {
                if (v2d[i] == '?');
                (v2d[i] = 'x');
            }
        }
        */

        cout << "" << endl;
        cout << "After Vector Update" << endl;
        for (int i = 0; i < v2d2.size(); i++) {
            for (int j = 0; j < v2d2[i].size(); j++)
                cout << v2d2[i][j] << " ";
            cout << endl;
        }

system("pause > NULL");
return 0;
}

当我尝试编译代码时，我收到以下错误消息。

IntelliSense：没有运算符“==”匹配这些操作数操作数类型是：std :: vector＆gt;，std :: allocator＆gt;＆gt;＆gt; == char Project3 \ Source.cpp 77 16 Project3

我认为容器在更新正确的行和列时存在问题。任何帮助将不胜感激。

谢谢

Answer 1

有一些错误，请与原始代码进行比较：

#include <iostream>
#include <vector>
using namespace std;


int main()
{
  // An empty vector of vectors
  vector<vector<char> > v2d;

  // Create a vector with 5 elements
  vector<char> v2(5, '?');

  // Create a vector of 3 elements. 
  vector<vector<char> > v2d2(3, v2);

  // Print out the elements
  cout << "Before Vector Update" << endl;
  for (int i = 0; i < v2d2.size(); i++) {
    for (int j = 0; j < v2d2[i].size(); j++)
      cout << v2d2[i][j] << " ";
    cout << endl;
  }

  for (int i = 0; i < v2d2.size(); i++) {
    for (int j = 0; j < v2d2[i].size(); j++)
      if (v2d2[i][j] == '?')
        v2d2[i][j] = 'x';
  }

  cout << "After Vector Update" << endl;
  for (int i = 0; i < v2d2.size(); i++) {
    for (int j = 0; j < v2d2[i].size(); j++)
      std::cout << v2d2[i][j] << " ";
    cout << endl;
  }


  return 0;
}

Answer 2

查看您评论的代码：

cout << "Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
    for (int j = 0; j < v2d2[i].size(); j++)
    {
        if (v2d[i] == '?'); // <------
        (v2d[i] = 'x');
    }
}

if语句后面有一个分号，表示如果语句为真，则不会执行任何操作。菜鸟错误。

许多人认为bad practice不要总是使用括号if - 语句和需要它们的其他类似情况，因为像这样的问题

Answer 3

你应该：

        if (v2d[i][j] == '?'){
            v2d[i][j] = 'x';
        }

Answer 4

    cout << "Vector Update" << endl;
    for (int i = 0; i < v2d2.size(); i++) {
        for (int j = 0; j < v2d2[i].size(); j++)
        {
            if (v2d[i][j] == '?')
                v2d[i][j] = 'x';
        }
    }

您没有正确访问2d向量，应该使用v2d [i] [j]。

替换2D矢量C ++中的数据

4 个答案: