Hi, Eljay! Thanks for the answer! Summary of the following posting: '-D_POSIX_SOURCE' does not help '-D_POSIX_C_SOURCE 199309L' helps Box with Intel ompiler is not available at the moment, can not tell the difference between gcc and icc. intro: "EL" == Eljay Love-Jensen <eljay@xxxxxxxxx> writes: EL> Hi Nickolay, The time.h header file is not part of GCC, it is supplied by EL> the OS. Yes, it is part of glibc (glibc-2.3 in my case) EL> The timespec structure is part of POSIX P1003.1b-1993 specification. EL> Does -D_POSIX_SOURCE change anything when you've -std=c99 ? No, plain -D_POSIX_SOURCE does not help. Output: ------------------------------------------------------------------------------- $ gcc -v -D_POSIX_SOURCE -std=c99 -c t.c Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/specs Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux Thread model: posix gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/cc1 -lang-c -v -D__GNUC__=3 -D__GNUC_MINOR__=2 -D__GNUC_PATCHLEVEL__=2 -D__GXX_ABI_VERSION=102 -D__ELF__ -D__unix__ -D__gnu_linux__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -Acpu=i386 -Amachine=i386 -D__i386 -D__i386__ -D__tune_i386__ -D_POSIX_SOURCE t.c -quiet -dumpbase t.c -std=c99 -version -o /tmp/ccg6vab1.s GNU CPP version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (cpplib) (i386 Linux/ELF) GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (i386-redhat-linux) compiled by GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5). ignoring nonexistent directory "/usr/i386-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/include /usr/include End of search list. t.c:4: storage size of `t' isn't known ------------------------------------------------------------------------------- -D_POSIX_C_SOURCE 199309L works (taken from glibc manual) $ gcc -v -D_POSIX_C_SOURCE=199309L -std=c99 -c t.c Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/specs Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux Thread model: posix gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/cc1 -lang-c -v -D__GNUC__=3 -D__GNUC_MINOR__=2 -D__GNUC_PATCHLEVEL__=2 -D__GXX_ABI_VERSION=102 -D__ELF__ -D__unix__ -D__gnu_linux__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -Acpu=i386 -Amachine=i386 -D__i386 -D__i386__ -D__tune_i386__ -D_POSIX_C_SOURCE=199309L t.c -quiet -dumpbase t.c -std=c99 -version -o /tmp/ccLQS7rJ.s GNU CPP version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (cpplib) (i386 Linux/ELF) GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (i386-redhat-linux) compiled by GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5). ignoring nonexistent directory "/usr/i386-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/include /usr/include End of search list. as -V -Qy -o t.o /tmp/ccLQS7rJ.s GNU assembler version 2.13.90.0.18 (i386-redhat-linux) using BFD version 2.13.90.0.18 20030206 EL> You may want to use -v to see what's going on with the command-line under EL> the covers. Compare "gcc -v -std=c99 -c t.c" versus "gcc -v -std=gnu99 EL> -c t.c", and see what kinds of freebie command line flags you're getting EL> under the covers. difference in cc1 invocation: -std=gnu99 adds the followin defines: -D__gnu_linux__ -Di386 -Dlinux -Dunix Log for -std=c99 ------------------------------------------------------------------------------- Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/specs Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux Thread model: posix gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/cc1 -lang-c -v -D__GNUC__=3 -D__GNUC_MINOR__=2 -D__GNUC_PATCHLEVEL__=2 -D__GXX_ABI_VERSION=102 -D__ELF__ -D__unix__ -D__gnu_linux__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -Acpu=i386 -Amachine=i386 -D__i386 -D__i386__ -D__tune_i386__ t.c -quiet -dumpbase t.c -std=c99 -version -o /tmp/ccpl8I8j.s GNU CPP version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (cpplib) (i386 Linux/ELF) GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (i386-redhat-linux) compiled by GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5). ignoring nonexistent directory "/usr/i386-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/include /usr/include End of search list. t.c:4: storage size of `t' isn't known ------------------------------------------------------------------------------- Log for -std=gnu99 ------------------------------------------------------------------------------- Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/specs Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux Thread model: posix gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/cc1 -lang-c -v -D__GNUC__=3 -D__GNUC_MINOR__=2 -D__GNUC_PATCHLEVEL__=2 -D__GXX_ABI_VERSION=102 -D__ELF__ -Dunix -D__gnu_linux__ -Dlinux -D__ELF__ -D__unix__ -D__gnu_linux__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -Acpu=i386 -Amachine=i386 -Di386 -D__i386 -D__i386__ -D__tune_i386__ t.c -quiet -dumpbase t.c -std=gnu99 -version -o /tmp/ccxs3CeY.s GNU CPP version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (cpplib) (i386 Linux/ELF) GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5) (i386-redhat-linux) compiled by GNU C version 3.2.2 20030222 (Red Hat Linux 3.2.2-5). ignoring nonexistent directory "/usr/i386-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/include /usr/include End of search list. as -V -Qy -o t.o /tmp/ccxs3CeY.s GNU assembler version 2.13.90.0.18 (i386-redhat-linux) using BFD version 2.13.90.0.18 20030206 ------------------------------------------------------------------------------- EL> HTH, --Eljay Nick.