What can cause strange gcc error "mode_t has not been declared" (and others) in system headers?

Question

This is the compiler message (somewhat stripped):

/usr/include/sys/mman.h:145: error: 'mode_t' has not been declared

Another error:

In file included from /usr/include/sys/resource.h:25,
                 from /usr/include/sys/wait.h:32,
/usr/include/bits/resource.h:172: error: field 'ru_utime' has incomplete type
/usr/include/bits/resource.h:174: error: field 'ru_stime' has incomplete type

And another one:

In file included from /usr/include/sys/wait.h:32,
/usr/include/sys/resource.h:94: error: 'id_t' has not been declared
/usr/include/sys/resource.h:98: error: 'id_t' has not been declared

This is on Linux, GCC 4.3.1. Do you have any clues why these happen?

It turned out to be issue with system header include inside a namespace. After that GCC became crazy. If anyone encounters similar problem, don't be surprised when the solution is totally unrelated to error messages. And be very careful when finding the cause.

Answer 1

have you tried to #include <sys/stat.h> and <sys/types.h>?

Answer 2

If these types are needed in e.g. the wait.h file, the types.h file should be included before including wait.h.

A way to investigate this: show the include tree your compiler generates for one of the offending compilation units. On Visual C++, this is the /showIncludes option. On gcc, I'm not so sure - it may be the -M option (which generates makefile-like output)

Answer 3

#include <fcntl.h>