已关闭此问题为not reproducible or was caused by typos。它目前不接受回答。

此问题是由打印错误或无法再重现的问题引起的。虽然类似的问题可能是on-topic在这里，这一个是解决的方式不太可能帮助未来的读者。
2个月前关闭。
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简而言之，.cpp文件中定义的全局常量变量（数组）从.o文件中消失，导致“未定义的引用.“错误。这个问题可以通过在变量的定义中添加”volatile“来不完美地解决。关闭编译器优化或'-flto'是没用的。
编译器：来自https://github.com/ZakKemble/avr-gcc-build/releases的AVR-GCC 11.10。
环境：PlatformIO.
操作系统：Windows 11
定义如下：

// file: oled_basic_init_sequence.cpp
#include <Arduino.h>
namespace  oled_basic {
    const uint8_t _init_sequence_for_ssd1316_4_wire_spi[25] PROGMEM = {
        0xae, /*display off*/
        0x00, /*set lower column address*/
        // ...
    };
    const uint8_t _init_sequence_for_ssd1306_2_wire_i2c[23] PROGMEM = {
        0xAE,
        0xD5,
        // ...
    };
}  // namespace oled_basic

不管有没有PROGMEM都没关系。在.h文件中：

// file: oled_basic_init_sequence.h
#pragma once
#include <stdint.h>
namespace oled_basic {
    extern const uint8_t _init_sequence_for_ssd1316_4_wire_spi[25];
    extern const uint8_t _init_sequence_for_ssd1306_2_wire_i2c[23];
}  // namespace oled_basic

在main.cpp文件中：

#include <Arduino.h>
#include "oled_basic_init_sequence.h"
volatile uint8_t * test = 0;
void setup() {
    *test = oled_basic::_init_sequence_for_ssd1316_4_wire_spi[0];
    
    // this doesn't help
    *test = pgm_read_byte(&(oled_basic::_init_sequence_for_ssd1316_4_wire_spi[0]));
}
void loop() {
}

编译失败，原因为：

Building in release mode
Compiling .pio\build\ATmega128\src\oled_basic_init_sequence.cpp.o
Linking .pio\build\ATmega128\firmware.elf
c:/users/xxxxx/.platformio/packages/toolchain-atmelavr/bin/../lib/gcc/avr/11.1.0/../../../../avr/bin/ld.exe: C:\Users\xxxxx\AppData\Local\Temp\ccelvOYl.ltrans0.ltrans.o: in function `main':
<artificial>:(.text.startup+0x5a): undefined reference to `_ZN10oled_basic37_init_sequence_for_ssd1316_4_wire_spiE'
collect2.exe: error: ld returned 1 exit status
*** [.pio\build\ATmega128\firmware.elf] Error 1
========================================================= [FAILED] Took 3.42 seconds =========================================================

详细构建信息：

avr-g++ -o .pio\build\ATmega128\firmware.elf -mmcu=atmega128 -Os -Wl,--gc-sections -flto -fuse-linker-plugin .pio\build\ATmega128\src\main.cpp.o .pio\build\ATmega128\src\oled_basic_font.cpp.o .pio\build\ATmega128\src\oled_basic_init_sequence.cpp.o -L.pio\build\ATmega128 -Wl,--start-group .pio\build\ATmega128\lib81f\libi2c.a .pio\build\ATmega128\lib685\libSPI.a .pio\build\ATmega128\libe29\libWire.a .pio\build\ATmega128\libFrameworkArduinoVariant.a .pio\build\ATmega128\libFrameworkArduino.a -lm -Wl,--end-group

也许我只是犯了一些低级的语法错误，仍然无法实现。