uint32_t a = 65536;
uint32_t b = 1 << 16;
Why is a != b here, but
uint32_t a = 65536;
uint32_t b = 65536;
here a == b although it should technically be the same?
I'm using CLion as an IDE and CMake 3.7.1 with Arduino CMake.
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aquaatic
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2Am I right to assume this is targeting an 8bit or 16bit microcontroller? – Marcus Müller Aug 06 '17 at 22:05
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ATMEGA 328P-PU, so 8-bit. And as always i figured it out myself seconds after posting: I need to cast the 1 to a uint32_t... – aquaatic Aug 06 '17 at 22:07
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1Could probably also write it as `1UL`. C has suffixes which change the type of literals. – Zan Lynx Aug 06 '17 at 22:11
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Thanks @ZanLynx, but that won't help much, because in reality i have to do things like this: `((uint32_t) ReadEeprom(address + 1) << 16)` – aquaatic Aug 06 '17 at 22:15
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Why doesn't `ReadEeprom` return a `uint32_t` then? – Zan Lynx Aug 06 '17 at 22:18
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1Never mind, I see what you're doing. I would do explicit assignments to declared variables of the right size, but whatever works. Casting is just fine. – Zan Lynx Aug 06 '17 at 22:22
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May you send a piece of code where we can see your issue? If you past a piece of code (also a function) we can better understand the problem. – Sir Jo Black Aug 09 '17 at 09:42
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Problem is solved, but thanks for trying to help – aquaatic Aug 09 '17 at 21:35
2 Answers
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uint32_t b = 1 << 16;
as you noticed, this breaks down if you don't cast 1 to a 32-bit integer first:
The literal 1 is the default integer type on your compiler. Don't know which, but it's either an 8 or a 16 bit int.
Now, assume it's an 16 bit in. When you shift 1 left 16 times, you just... well, it doesn't make sense. So, make your 1 a 32 bit int first, then shift.
Marcus Müller
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