error: redefinition of ‘xxx‘

Problem description

Arduino Import the project PlatformIO Compilation encountered error: redefinition of ‘xxx’…note: ‘float humidity’ previously defined here, Twenty errors are reported during compilation , It's all a mistake ：

Cause analysis ：

What you find on the Internet is said to be the target header file .h No conditional compilation statement ：

#ifndef _TEST_H_
#define _TEST_H_

//...

#endif

Then I found that the header file I introduced has added conditional compilation statements , Later, it was found that there were two projects .ino file , Although the two file names are different , But the content is the same （ Before I import, there is no co2-sensor-main.ino Of this file , I don't know how it came about ）, Then I delete one , The compilation passed .
Mainly these two sentences ,***In file included from C:/Users/Administrator/Documents/PlatformIO/Projects/220614-094530-huzzah/src/co2-sensor-main.ino:4:
src\thermometer.h:8:7: error: redefinition of ‘Adafruit_SSD1306 display’
***In file included from C:/Users/Administrator/Documents/PlatformIO/Projects/220614-094530-huzzah/src/co2-sensor.ino:4:
src\thermometer.h:8:7: note: ‘Adafruit_SSD1306 display’ previously declared here
Redefinition “Adafruit_SSD1306 display”
Be careful :'Adafruit_SSD1306 display’ It was stated here before
Bold font from here we can feel that there are repeated references in the two documents , Then I open the comparison , Find the same code , So after deleting one , Try to compile , This time it passed .

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There is a boss to point out why there is an extra one .ino Documents