imgui: InputText doesn't update its content

Version/Branch of Dear ImGui:

Version: v1.89.8 Branch: master

Back-end/Renderer/Compiler/OS

Back-ends: SFML, OpenGL (https://github.com/SFML/imgui-sfml) Compiler: GCC (G++) Operating System: Windows 10

My Issue/Question:

I observed that if the variable is declared as static (variable required: std::string* str in imgui_stdlib InputText, second argument), the content within InputText does not update, but it can be edited. Conversely, if the variable is not static, the content within InputText updates, but it cannot be edited.

Screenshots/Video

Reference on static variable: test_3HP2yuMaNx

Reference on non-static variable: test_vILVVNTYoN

Standalone, minimal, complete and verifiable example: (see https://github.com/ocornut/imgui/issues/2261)

// Includes.
#include "SFML\include\SFML\Graphics.hpp"

#include "imgui\include\imgui.h"
#include "imgui\include\imgui-SFML.h"
#include "imgui\include\imgui_stdlib.h"

#include <iostream>

int main() {
    sf::RenderWindow window(sf::VideoMode(500, 500), "Hello!");

    ImGui::SFML::Init(window);

    sf::Clock clock;

    while(window.isOpen()) {
        ImGui::SFML::Update(window, clock.restart());

        sf::Event event;

        ImGui::Begin("yummi");

        while(window.pollEvent(event)) {
            ImGui::SFML::ProcessEvent(event);

            if(event.type == sf::Event::Closed) {
                window.close();
            }
        }

        // Main issues begin.
        static bool check = true;

        ImGui::Checkbox("checkbox", &check);

        static std::string inputContent = check ? "hello world" : "bye world"; // remove / or add 'static' to see difference

        ImGui::InputText("input", &inputContent);
        // Main issues end.

        ImGui::End();

        window.clear();

        ImGui::SFML::Render(window);

        window.display();
    }

    return 0;
}

When inputContent is static, the content does not get updated. However, it is possible to edit the content inside the Input. Whereas when inputContent is not static, the content gets updated and, in that case, it is impossible to edit the content in the input. Any thoughts?

About this issue

Original URL
State: closed
Created 10 months ago
Comments: 21 (10 by maintainers)

Most upvoted comments

Things are behaving exactly as they should.

This is a C++ understanding issue and on your insistence to open issues without reading our answers I am going to close this. Please investigate by yourself.

ocornut on Aug 16, 2023

It seems like you don’t understand the static keyword. If you use static, it’s only initiated once, consider the following code:

void increase(){
    static int value = 0;
    std::court << value << " ";
    value += 1;
}
increase();
increase();
increase();

Will output: 0 1 2, this is because value is only set to 0 once. Without the static keyword, the output would be: 0 0 0, because value is set to 0 every time.

So with static, the text can be edited, but the checkbox doesn’t work because = check ? "hello world" : "bye world"; is only executed once. And without static, the text couldn’t be edited because it’d reset every loop. This is expected behavior.

To achieve your goal, do this instead:

static std::string inputContent = check ? "hello world" : "bye world";

// ImGui::Checkbox returns true if it was clicked on
if (ImGui::Checkbox("checkbox", &check))
{
    inputContent = check ? "hello world" : "bye world";
}

ImGui::InputText("input", &inputContent);

sakiodre on Aug 16, 2023

If your string is static, it gets initialized once when the static is first encountered. It isn’t “updated” (or rather reinitialized) each iteration. That is how static works, don’t use static if that is not your intended behavior.

Without the static, the string is not impossible to edit. You are editing it. But then on the very next iteration of your loop, you overwrite the string yourself, loosing your edit again. It is your code doing this, it is not a problem with ImGui itself.

The same goes for your other issue. It is a bug in your code (despite your insistence that you don’t have any bugs, that would be a bold claim even for experienced programmers) that stems from a wrong understanding of the C++ language.

GamingMinds-DanielC on Aug 16, 2023

I’ve been trying to fix this for a few days. Is it that difficult to write a solution that, I wager, will take no more than one line?

xzripper on Aug 16, 2023