Hi
In reference to my previous thread
https://community.arm.com/support-forums/f/keil-forum/54074/keil-packunzip-ece-problem
I'm wondernig what is the difference between c99 and gnu99 C-standard which i can select in compiller options?
Which one should be chosen?
Why Keil changed Arm Compiler to version 6? Is it possible to use Ver 5?
Please understand that Keil won't recommend any selection of a C Standard for a customer project (reason, i.e. unknown project specification)
See "C Standards": https://developer.arm.com/documentation/ka004425/latest
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You can manually install Arm Compiler 5 by following
"Can I add Arm Compiler 5 to Keil MDK 5.37 or newer?"
https://developer.arm.com/documentation/ka005073/latest
The main difference between -std=c99 and -std=gnu99 is the support of extra GNU extensions:
https://developer.arm.com/documentation/101754/0619/armclang-Reference/armclang-Command-line-Options/-std