The messages produced by the NAG Fortran Compiler itself during compilation are intended to be self-explanatory. The linker, or more rarely the host C compiler, may produce occasional messages.
Messages produced by the compiler are classified by severity level; these levels are:
| Remark | a comment about the source code (this is the least important class of informational message). |
| Info | informational message, noting an aspect of the source code in which the user may be interested. |
| Note | an informational message of greater import than “Info”. |
| Warning | the source code appears likely to be in error. |
| Questionable | some questionable usage has been found in the source code which may indicate a programming error. This has the same severity as “warning”. |
| Extension | some non-standard-conforming source code has been detected but has successfully been compiled as an extension to the language. This has the same severity as “warning”. |
| Obsolescent | some archaic source code has been detected which although standard-conforming was classified as obsolescent by the Fortran standard (selected according to the -f95, -f2003 and -f2008 options). This has the same severity as “warning”. |
| Deleted feature used | a feature that was present in an older Fortran standard but deleted from the Fortran standard selected by a -fN option was used. This has the same severity as “warning”. |
| Error | the source code does not conform to the Fortran standard or does not make sense. Compilation continues after recovery. |
| Fatal | a serious error in the user's program from which the compiler cannot recover, the compilation is immediately terminated. |
| Panic | an internal inconsistency is found by one of the compiler's self-checks; this is a bug in the compiler itself and NAG should be notified. |