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How to use C++ main.cpp with PlatformIO on ESP32 / esp-idf

When you are using PlatformIO to compile your firmware, it is easily possible to use a C++ main.cpp instead of the pure C main.c by just renamingmain.c to main.cpp

However, you also need to properly declary app_main(). After the #include section of your main.cpp (or at the top of the file if you don’t have an #include section yet), add this code:

app_main_declare.cpp
extern "C" {
    void app_main(void);
}

This will tell the compiler that app_main() is a C function, not a C++ function.

Full main.cpp example

espidf_main_cpp_example.cpp
#include <cstdio>
#include <freertos/FreeRTOS.h>
#include <freertos/task.h>

extern "C" {
    void app_main(void);
}

void app_main() {
    while(true) {
        printf("Hello PlatformIO!\n");
        // Wait for one second
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}
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