# \#ifndef Definition Specification

**URL:** <https://forum.arduino.cc/t/ifndef-definition-specification/1336813>\
**Category:** Programming\
**Created:** [December 29, 2024, 9:09am UTC](https://forum.arduino.cc/t/ifndef-definition-specification/1336813 "2024-12-29T09:09:10Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![UniquePete](https://avatars.discourse-cdn.com/v4/letter/u/d6d6ee/32.png) [@UniquePete](https://forum.arduino.cc/u/UniquePete)\
**Post date:** [December 29, 2024, 11:00pm UTC](https://forum.arduino.cc/t/ifndef-definition-specification/1336813/9 "2024-12-29T23:00:20Z")

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OK, maybe this thread

> [@Preprocessor problem](https://forum.arduino.cc/t/preprocessor-problem/696970):
>
> Hi! I'm facing a strange problem... On my main ino file, on first line, i have a definition: #define MYDEF #include "Ethernet.h" Then i include the ethernet library, modified in this way: #ifndef W5100\_H\_INCLUDED #define W5100\_H\_INCLUDED #define SPI\_ETHERNET\_SETTINGS SPISettings(14000000, MSBFIRST, SPI\_MODE0) #pragma message "14" ... #if defined(MYDEF) #pragma message "4" #undef SPI\_ETHERNET\_SETTINGS #define SPI\_ETHERNET\_SETTINGS SPISettings(4000000, MSBFIRST, SPI\_MODE0) #endif ... #en…

explains the situation... What I want can't be done through the IDE, maybe unless I'm willing to get under the covers and use the CLI, which I didn't even know existed.

If I've misinterpreted the essence of the explanations provided in this thread, I'd still love to hear how I can solve my particular problem, or if @pert is out there and can confirm my [unwelcome] suspicion, I'd be [not so] happy to have my conclusion confirmed.

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