This diagnostic rule is based on the software development guidelines developed by AUTOSAR (AUTomotive Open System ARchitecture).
This diagnostic varies for C and C++.
C: the suffix 'L' should be used instead of 'l'.
C++: all literal suffixes should be uppercase.
Using lowercase suffixes obscures the code. For example, you may confuse an 'l' suffix with the numeral one (1), which could cause various mistakes.
Here are examples of literals triggering this warning:
12l; 34.0f; 23u;
The warning is not issued when the literals are written in the following form:
12L; 34.0F; 23U;