如何修复 ROOT 错误：'gROOT' was not declared in this scope
问题：
编译基于 ROOT 的 C++ 程序时，你收到如下错误消息：
groot_not_declared_error.txt
main.cpp: In member function ‘int main()’:
main.cpp:26:22: error: ‘gROOT’ was not declared in this scope; did you mean ‘ROOT’?
26 | auto cdpad = gROOT->GetSelectedPad();解决方案：
错误消息有点误导。问题是 gROOT 对象在全局作用域中不可用。你需要包含 ROOT 头文件 TROOT.h 才能访问它。在源文件顶部包含以下行：
include_troot.cpp
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