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    <p>The output of the <code>size</code> command is a good starting place, but does not give you all of the information you need.</p> <pre><code>$ avr-size program.elf text data bss dec hex filename </code></pre> <p>The size of your image is usually a little bit more than the sum of the text and the data sections. The bss section is essentially compressed because it is all 0s. There may be other sections which are relevant which aren't listed by size.</p> <p>If your build system is set up like ones that I've used before for AVR microcontrollers then you will end up with an *.elf file as well as a *.bin file, and possibly a *.hex file. The *.bin file is the actual image that would be stored in the program flash of the processor, so you can examine its size to determine how your program is growing as you make edits to it. The *.bin file is extracted from the *.elf file with the objdump command and some flags which I can't remember right now.</p> <p>If you are wanting to know how to guess-timate how your much your C or C++ code will produce when compiled, this is a lot more difficult. I have observed a 10x blowup in a function when I tried to use a uint64_t rather than a uint32_t when all I was doing was incrementing it (this was about 5 times more code than I thought it would be). This was mostly to do with gcc's avr optimizations not being the best, but smaller changes in code size can creep in from seemingly innocent code.</p> <p>This will likely be amplified with the use of C++, which tends to hide more things that turn into code than C does. Chief among the things C++ hides are destructor calls and lots of pointer dereferencing which has to do with the <code>this</code> pointer in objects as well as a secret pointer many objects have to their virtual function table and class static variables. </p> <p>On AVR all of this pointer stuff is likely to really add up because pointers are twice as big as registers and take multiple instructions to load. Also AVR has only a few register pairs that can be used as pointers, which results in lots of moving things into and out of those registers.</p> <p>Some tips for small programs on AVR:</p> <ul> <li><p>Use <code>uint8_t</code> and <code>int8_t</code> instead of <code>int</code> whenever you can. You could also use <code>uint_fast8_t</code> and <code>int_fast8_t</code> if you want your code to be portable. This can lead to many operations taking up only half as much code, because <code>int</code> is two bytes.</p></li> <li><p>Be very aware of things like string and struct constants and literals and how/where they are stored.</p></li> <li><p>If you're not scared of it, read the AVR assembly manual. You can get an idea of the types of instructions, and from that the type of C code that easily maps to those instructions. Use that kind of C code.</p></li> </ul>
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    1. POHow much is 32 kB of compiled code
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    1. COThank you for your answer, particularly for all the practical advises.
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    2. CO@Klaus: If you think the answer is useful, you should mark it as the accepted answer. :)
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