storage size of ‘oldact’ isn’t known

#include <signal.h>

int main()
{
struct sigaction act, oldact;
return 0;
}


dies with the message

testgcc4.c: In function ‘main’:
testgcc4.c:6: error: storage size of ‘act’ isn’t known
testgcc4.c:6: error: storage size of ‘oldact’ isn’t known

if I use -std=c99 or --ansi?
gcc testgcc4.c compiles without problem but adding -std=c99 or --ansi produces 
the error message above (for any of gcc-3.4, gcc-4.0, gcc-4.1) but neither

icc nor gcc on FreeBSD has a problem with -std=c99 or --ansi

Sumarry：

use -std=gnu99 on linux if you need some C99 functions (e.g. strtof) but also want to use functions like sigaction and strtok_r

gcc on linux is stricter than gcc on FreeBSD (or icc on either FreeBSD or linux) concerning standards.
gcc -std=c99 on linux means: *only* recognize functions specified in the standard (no sigaction, no strtok_r etc)
gcc -std=c99 on FreeBSD or icc -std=c99 on either FreeBSD or linux means recognize functions specified in the standard. This corresponds more or less to -std=gnu99 on linux

PS. This trap seems to be quite common (e.g. discussions on debian-glibc about the "fact" that strtof is completely broken on linux). I would be grateful if somebody could point me to a good overview describing what standards compliance means for various OS/compiler+options/standards combinations.

上面的代码使用-std=gnu99正常通过。

man gnu:

c99
c9x
iso9899:1999
iso9899:199x
ISO C99. Note that this standard is not yet fully supported; see <http://gcc.gnu.org/c99status.html> for
more information. The names c9x and iso9899:199x are deprecated.

gnu99
gnu9x
GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, this will become the default. The name
gnu9x is deprecated.

参考 :http://blog.csdn.net/cccallen/article/details/8440175