c# - 为什么我的 C++ Windows 窗体中有 C# 代码，而 C++ 函数弹出错误？

Question

我的任务是构建一个简单的计算器作为 C++ Windows 窗体。

现在它是一个文本框和一个按钮，文本框的示例输入是 3 + 2，按钮应该在同一个文本框上打印它们的结果。

我创建了一个新项目 -> C++ Windows 窗体:

但是有些代码是自动生成的，看起来像C#代码，我以前没见过。

添加按钮和文本框后的原始代码:

#pragma once

namespace CppWinForm1 {

    using namespace System;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;

    /// <summary>
    /// Summary for MyForm
    /// </summary>
    public ref class MyForm : public System::Windows::Forms::Form
    {
    public:
        MyForm(void)
        {
            InitializeComponent();
            //
            //TODO: Add the constructor code here
            //
        }

    protected:
        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        ~MyForm()
        {
            if (components)
            {
                delete components;
            }
        }
    private: System::Windows::Forms::Button^  button1;
    private: System::Windows::Forms::TextBox^  textBox1;
    protected:

    private:
        /// <summary>
        /// Required designer variable.
        /// </summary>
        System::ComponentModel::Container ^components;

#pragma region Windows Form Designer generated code
        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        void InitializeComponent(void)
        {
            this->button1 = (gcnew System::Windows::Forms::Button());
            this->textBox1 = (gcnew System::Windows::Forms::TextBox());
            this->SuspendLayout();
            // 
            // button1
            // 
            this->button1->Location = System::Drawing::Point(59, 81);
            this->button1->Name = L"button1";
            this->button1->Size = System::Drawing::Size(75, 23);
            this->button1->TabIndex = 0;
            this->button1->Text = L"button1";
            this->button1->UseVisualStyleBackColor = true;
            this->button1->Click += gcnew System::EventHandler(this, &MyForm::button1_Click);
            // 
            // textBox1
            // 
            this->textBox1->Location = System::Drawing::Point(59, 31);
            this->textBox1->Name = L"textBox1";
            this->textBox1->Size = System::Drawing::Size(100, 22);
            this->textBox1->TabIndex = 1;
            // 
            // MyForm
            // 
            this->AutoScaleDimensions = System::Drawing::SizeF(8, 16);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(282, 253);
            this->Controls->Add(this->textBox1);
            this->Controls->Add(this->button1);
            this->Name = L"MyForm";
            this->Text = L"MyForm";
            this->ResumeLayout(false);
            this->PerformLayout();

        }
#pragma endregion

    }

    };
}

当我在上面的文件 (MyForm.h) 中添加我的内容时:

#include <string>
#include <msclr\marshal_cppstd.h> // for converting String^ to string

using namespace std;

// ..

private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
{
    System::String^ temp = textBox1->Text; // system string
    std::string InputString = msclr::interop::marshal_as<std::string>(temp); // convert to standard string

    int FirstNumber = 0,
        SecondNumber = 0,
        Result = 0,
        MyInc = 1;
    char MyOperator;

    int SpaceIndex = InputString.find(' ');

    for (int i = SpaceIndex - 1; i >= 0; i--)
    {
        FirstNumber += InputString[i].ToInt32() * MyInc;
        MyInc *= 10;
    }

    MyOperator = InputString[SpaceIndex + 1];

    InputString = InputString.substr(0, SpaceIndex + 2);

    MyInc = 1;

    for (int i = InputString.length() -1; i >= 0; i--)
    {
        FirstNumber += InputString[i].ToInt32() * MyInc;
        MyInc *= 10;
    }

    if (MyOperator == '+')
        Result = FirstNumber + SecondNumber;

    textBox1->Text = Result.ToString();

我在 .ToInt32() 函数上遇到此错误:

Too few arguments for the function call

同样在MyForm.Cpp(我没碰过)也有同样的错误:

#include "MyForm.h"

using namespace System;
using namespace System::Windows::Forms;

[STAThread]
void Main(array<String^>^ args) // Error here saying too few Arguments
{
    Application::EnableVisualStyles();
    Application::SetCompatibleTextRenderingDefault(false);

    CppWinForm1::MyForm form;
    Application::Run(%form);
}

有人能告诉我为什么会这样吗？请和谢谢

Answer 1

生成的代码是 C++/CLI，标准 C++ 的超集。请注意，它不是 C#。有许多差异，例如命名空间分隔符是 :: vs .，或 ref class 上下文关键字。 C++/CLI 编译为 MSIL(托管代码)，但可以包含 native C++，生成所谓的混合模式程序集。它主要用于托管/非托管互操作。

您为 InputString[i].ToInt32() 收到的编译器错误有点误导。这是语言复杂性的结果，编译器尝试了所有可能的方法来解释表达式，当它最终放弃时，它遇到的错误并不总是最容易理解的。

在这种情况下，InputString[i] 调用 std::string::operator[] ，它返回对 char 的引用。这是C++中的整型数据类型，不是有成员方法的类类型。如果您需要将字符串或字符转换为整数，则必须使用其他方法，例如std::stoi :

int number = std::stoi(std::string(InputString[i]));