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ESP32 C++17 toolchain missing std::optional

I’ve been trying to get C++17 working, and for the most part it seemed to be working, but there is no std::optional in there.

My platformio.ini looks like this:

[env]
build_unflags = -std=gnu++11
build_flags = -std=c++17

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200

If I have #include <optional> in my code, the error I get is:

In file included from src/main.cpp:12:0: fatal error: optional: No such file or directory

How can I get a fully working C++17 toolchain for ESP32?

After some time looking for answers, I’m just left even more confused about the different toolchains. What is the difference, for example, between toolchain-xtensa32 and toolchain-xtensa-esp32 and which one should I use? When I include toolchain-xtensa-esp32 it still uses the other one to build my application…

Looking into the contents of toolchain-xtensa32 it does have the optional header, so not sure why the toolchain can’t find it.

I updated to the platform you linked to, and it finally uses gcc 8.4, so that’s great news. But now I have an issue with the FreeRTOS.h header, AFAIK the ESP-IDF should contain FreeRTOS as well, so did something get renamed or what?

In file included from src/main.cpp:12: fatal error: FreeRTOS.h: No such file or directory

Ok, FreeRTOS.h header moved

before: #include <FreeRTOS.h>
after: #include <freertos/FreeRTOS.h>

Hi, @petoknm how did you manage to fix this? I’m using the following platformio.ini config, and keep receiving:
fatal error: optional: No such file or directory

[env]
build_unflags = -std=gnu++11
build_flags = -std=c++17

[env:esp32doit-devkit-v1]
platform = https://github.com/tasmota/platform-espressif32/releases/download/v2.0.2idf/platform-espressif32-2.0.2.zip
board = esp32doit-devkit-v1
framework = arduino

monitor_speed = 115200

extra_scripts = 
	...

lib_deps = 
	...

Rather use gnu++17, I’ve seen it needing GNU extensions.

Works for me.

[env:esp32doit-devkit-v1]
platform = https://github.com/tasmota/platform-espressif32/releases/download/v2.0.2idf/platform-espressif32-2.0.2.zip
board = esp32doit-devkit-v1
framework = arduino
build_unflags = -std=gnu++11
build_flags = -std=gnu++17
#include <Arduino.h>
#include <optional>

void setup(){}
void loop(){}

>pio run
Processing esp32doit-devkit-v1 (platform: https://github.com/tasmota/platform-espressif32/releases/download/v2.0.2idf/platform-espressif32-2.0.2.zip; board: esp32doit-devkit-v1; framework: arduino)
------------------------------------------------------------------------------------------------------------------------
Verbose mode can be enabled via `-v, --verbose` option
CONFIGURATION: https://docs.platformio.org/page/boards/espressif32/esp32doit-devkit-v1.html
PLATFORM: Espressif 32 (2.0.2) > DOIT ESP32 DEVKIT V1
HARDWARE: ESP32 240MHz, 320KB RAM, 4MB Flash
DEBUG: Current (esp-prog) External (esp-prog, iot-bus-jtag, jlink, minimodule, olimex-arm-usb-ocd, olimex-arm-usb-ocd-h, olimex-arm-usb-tiny-h, olimex-jtag-tiny, tumpa)
PACKAGES:
 - framework-arduinoespressif32 2.0.2
 - tool-esptoolpy 1.30200.211025 (3.2.0)
 - tool-mklittlefs 1.203.210628 (2.3)
 - toolchain-xtensa-esp32 8.4.0+2021r2
LDF: Library Dependency Finder -> https://bit.ly/configure-pio-ldf
LDF Modes: Finder ~ chain, Compatibility ~ soft
Found 30 compatible libraries
Scanning dependencies...
No dependencies
Building in release mode
Compiling .pio\build\esp32doit-devkit-v1\src\main.cpp.o
Generating partitions .pio\build\esp32doit-devkit-v1\partitions.bin
Archiving .pio\build\esp32doit-devkit-v1\libFrameworkArduinoVariant.a
Indexing .pio\build\esp32doit-devkit-v1\libFrameworkArduinoVariant.a
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\Esp.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\FirmwareMSC.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\FunctionalInterrupt.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\HWCDC.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\HardwareSerial.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\IPAddress.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\IPv6Address.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\MD5Builder.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\Print.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\Stream.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\StreamString.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\USB.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\USBCDC.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\USBMSC.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\WMath.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\WString.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\base64.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\cbuf.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-adc.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-bt.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-cpu.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-dac.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-gpio.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-i2c-slave.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-i2c.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-ledc.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-matrix.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-misc.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-psram.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-rmt.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-sigmadelta.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-spi.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-time.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-timer.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-tinyusb.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-touch.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\esp32-hal-uart.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\firmware_msc_fat.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\libb64\cdecode.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\libb64\cencode.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\main.cpp.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\stdlib_noniso.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\wiring_pulse.c.o
Compiling .pio\build\esp32doit-devkit-v1\FrameworkArduino\wiring_shift.c.o
Archiving .pio\build\esp32doit-devkit-v1\libFrameworkArduino.a
Indexing .pio\build\esp32doit-devkit-v1\libFrameworkArduino.a
Linking .pio\build\esp32doit-devkit-v1\firmware.elf
Retrieving maximum program size .pio\build\esp32doit-devkit-v1\firmware.elf
Checking size .pio\build\esp32doit-devkit-v1\firmware.elf
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [          ]   4.2% (used 13668 bytes from 327680 bytes)
Flash: [=         ]  12.5% (used 163249 bytes from 1310720 bytes)
Building .pio\build\esp32doit-devkit-v1\firmware.bin
esptool.py v3.2
Merged 2 ELF sections
=====================[SUCCESS] Took 11.05 seconds =====================
2 Likes

This totally works! Awesome! Thank you very much :rocket: