Question

I am learning Visual C++ and have come across quite the stumbling block on Day 1. I am attempting to make a simple ‘Hello World’ application using the Form template in Visual C++ 2010.

The solution created Form1.h, resource.h, stdafx.h, AssemblyInfo.cpp, helloworld.cpp, and stdafx.cpp. I added a button and a label to Form1 and was able to make it so that when the button is clicked the label changed text to “Hello World” from within Form1.h. I would like to do this from Form1.cpp though, so I stripped the code from the header. I currently have the following code:

Form1.cpp

#include "stdafx.h"
#include "stdio.h"
#include "Form1.h"

using namespace helloworld;


helloworld::Void testButton_Click(System::Object^  sender, System::EventArgs^  e) {
    helloworld::Form1::label1->Text = "Test";
}

Form1.h

#pragma once

namespace helloworld {

    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 Form1
    /// </summary>
    public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        Form1(void)
        {
            InitializeComponent();
            //
            //TODO: Add the constructor code here
            //
        }

    protected:
        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        ~Form1()
        {
            if (components)
            {
                delete components;
            }
        }
    private: System::Windows::Forms::Button^  testButton;
    public: System::Windows::Forms::Label^  label1;
    protected: 

    private:
        /// <summary>
        /// Required designer variable.
        /// </summary>testButton
        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->testButton = (gcnew System::Windows::Forms::Button());
            this->label1 = (gcnew System::Windows::Forms::Label());
            this->SuspendLayout();
            // 
            // testButton
            // 
            this->testButton->Location = System::Drawing::Point(136, 159);
            this->testButton->Name = L"testButton";
            this->testButton->Size = System::Drawing::Size(75, 23);
            this->testButton->TabIndex = 0;
            this->testButton->Text = L"Test Button";
            this->testButton->UseVisualStyleBackColor = true;
            this->testButton->Click += gcnew System::EventHandler(this, &Form1::testButton_Click);
            // 
            // label1
            // 
            this->label1->AutoSize = true;
            this->label1->Location = System::Drawing::Point(125, 100);
            this->label1->Name = L"label1";
            this->label1->Size = System::Drawing::Size(35, 13);
            this->label1->TabIndex = 1;
            this->label1->Text = L"label1";
            // 
            // Form1
            // 
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(284, 262);
            this->Controls->Add(this->label1);
            this->Controls->Add(this->testButton);
            this->Name = L"Form1";
            this->Text = L"Form1";
            this->Load += gcnew System::EventHandler(this, &Form1::Form1_Load);
            this->ResumeLayout(false);
            this->PerformLayout();

        }
#pragma endregion
    private: System::Void testButton_Click(System::Object^  sender, System::EventArgs^  e) ;
private: System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e) {
         }
    };
}

With this code I receive the following error:

error C2227: left of '->Text' must point to class/struct/union/generic type

From what I have found, that error means that the program doesn’t know what I am talking about with label1->Text. I would greatly appreciate any help that could be given to a Visual C++ newbie.

Answer 1

The problem is in the following snippet:

helloworld::Void testButton_Click(System::Object^  sender, System::EventArgs^  e) {
    helloworld::Form1::label1->Text = "Test";
}

helloworld::Form1 is the type of your form; it is not the actual instance. We use the this keyword to refer to the current object instance (most of the time the this keyword is optional). Another problem is helloworld::Void, which should be System::Void. You also need to replace testButton_Click with Form1::testButton_Click to show that this is a class method and not a free function. Your code should become:

System::Void Form1::testButton_Click(System::Object^  sender, System::EventArgs^  e) {
    label1->Text = "Test";
}

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Note: You should use C# when working with windows forms. C++/CLI is a mess of a language and the majority of people use C++/CLI only when combining managed with native code.