storage size of ‘oldact’ isn’t known

最新推荐文章于 2023-07-20 16:52:42 发布

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本文探讨了GCC编译器在不同标准模式下对C99函数的支持情况，特别是使用-std=c99或--ansi选项时的行为差异，并对比了GCC在Linux与FreeBSD平台上的表现。

#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.