当包含math.h库时，程序内存不会增加

Question

I'm a bit of a newbie to the Atmel world. Once Upon a time I could write and compile C with Visual Studio but am a bit out of practice.

So I'm trying to get an understanding of memory usage in a microcontroller ATTINY1616 . I opened Atmel studios, created a C executable project and chose the correct microcontroller. I build the project which has next to nothing in it and see that the program memory is 154 bytes . This is my baseline.

Now I tried to add the line #include <math.h> to see if my program memory usage would increase. It didn't. Then I tried adding float a = 2.000678f; inside the main . Still no increases after building the project. What am I misunderstanding here?

/*
* GccApplication2.c
*
* Created: 12/20/2018 9:21:43 PM
* Author : joely
*/ 

#include <avr/io.h>
#include <math.h>

int main(void)
{ 
    float a = 2.000678f;
    /* Replace with your application code */
    while (1) 
    {
    }
}

Answer 1

Header files typically only contain declarations of functions, not the definitions .

You're not using any of the functions declared in math.h, so the library they reside in isn't getting linked into your program. If you use one of them, for example float b = sin(a) , then the contents of the math library is required and is linked in (assuming you pass -lm to gcc to do so).

Answer 2

So after asking some friends with microcontroller experience I found the solution.

In Atmel Studio you need to go to Project-->Application Properties--->Toolchain and Change optimization to none.

Then it recognizes my floats and stores them in program memory, and when atan() is used to perform a calc it also fills up the space with the same above code.