C++ std::vector 问题 (imgui)

Question

I've had this issue for a while now and I'm not sure exactly how to fix it.

Here's the issue:

std::vector<const char*> arr = {};
static char input[48] = "";
ImGui::InputTextWithHint("##Input", "Put your input here", input, IM_ARRAYSIZE(input));

if (ImGui::Button("add to array")){
arr.pushback(input);
}

When I press add, it adds the input into the vector, but if I press add again and change the text, it changes all pushed items of the vector to the input text. Can anyone help?

Answer 1

You are pushing the same pointer to the array each time. You would have to allocate a new string with the buffer's contents after pressing the button.

if (ImGui::Button("add to array")){
  char* inputS = (char*)malloc((strlen(input) + 1) * sizeof(*input));  // allocate a separate string
  strcpy(inputS, input);        // copy until the first \0 byte is reached 
  arr.pushback(inputS);
}

This is C-style, which some people might not want to see in modern C++. You can do the same thing by declaring your array as std::vector<std::string> , which would make it so that when you push a new element to the vector, the constructor of std::string that takes const char* will be called (which is somewhat similar to the C-version).

So just

std::vector<std::string> arr;

if (ImGui::Button("add to array")){
  arr.pushback(input); // const char* input will be copied to the new std::string element of the array
}

ImGUI is a C-API, which means it doesn't understand std::string . To use std::string with ImGUI, you can use it's .data() (or .c_str() ) method to access it's const char* data pointer.