8.1.3 Header is ‘present but cannot be compiled’

On some platforms ./configure may output one or more warnings of the following form:

WARNING: filename.h: present but cannot be compiled
WARNING: filename.h:     check for missing prerequisite headers?
WARNING: filename.h: see the Autoconf documentation
WARNING: filename.h:     section "Present But Cannot Be Compiled"
WARNING: filename.h: proceeding with the preprocessor's result
WARNING: filename.h: in the future, the compiler will take precedence
WARNING:     ## ----------------------------- ##
WARNING:     ## Report this to pakin@lanl.gov ##
WARNING:     ## ----------------------------- ##

Typically, such warnings indicate that the header file in question was written for one compiler but a different compiler is being used to build coNCePTuaL. Unless the header file in question poses problems during the run of make, the ‘present but cannot be compiled’ warnings can be ignored and there is no need to report the compiler-preprocessor mismatch to the e-mail address shown.