How can I perform pre-main initialization in C/C++ with avr-gcc?

c++ c initialization arduino avr-gcc
Matthew Murdoch picture Matthew Murdoch · Jun 4, 2009 · Viewed 9.5k times · Source

In order to ensure that some initialization code runs before main (using Arduino/avr-gcc) I have code such as the following:

class Init {
public:
    Init() { initialize(); }
};

Init init;

Ideally I'd like to be able to simply write:

initialize();

but this doesn't compile...

Is there a less verbose way to achieve the same effect?

Note: the code is part of an Arduino sketch so the main function is automatically generated and cannot be modified (for example to call initialize before any other code).

Update: ideally the initialization would be performed in the setup function, but in this case there is other code depending on it which occurs before main.

Answer

Adam Rosenfield picture Adam Rosenfield · Jun 4, 2009

You can use GCC's constructor attribute to ensure that it gets called before main():

void Init(void) __attribute__((constructor));
void Init(void) { /* code */ }  // This will always run before main()

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