问题
I am getting the following error:
error C3646: '__attribute__': unknown override specifier
Code:
LEMUR_PREALIGN char _stack[ sizeof(_Type) * _Count ] LEMUR_POSTALIGN;
Complete error:
1>c:\program files\indri\indri 5.9\include\indri\greedy_vector(52): error C3646: '__attribute__': unknown override specifier
Additional info: I am trying to use indri.lib in Visual Studio project.
回答1:
The __attribute__ command is a compiler specific command to gcc. And it is used on line 52 of this file with the ((align)) command, which:
Specifies a minimum alignment (in bytes) for variables of the specified type
Visual studio does in fact have a similar alignment command: align. But there are two problems:
__declspec(align(#))does not support the defaulted:__attribute__ ((aligned))behavior which will:
Align a type to the maximum useful alignment for the target machine you are compiling for
__declspec(align(#))is a prefix.__attribute__((aligned(#)))is a suffix. This means that your actual code would need to differ on the placement:
struct S { short f[3]; } __attribute__ ((aligned)); // gcc alignment definition
__declspec(align(16)) strict S { short f[3]; }; // MSVC alignment
The point here is you'd probably be better off #ifdefing by compiler any line that uses __attribute__ ((aligned)) and cooking your own __declspec(align(#)).
For more info see: GCC vs MSVC class packing and alignment
After a bit more study into lemur_platform.h it looks like the code has already done all the above work for you! You'll notice that #define LEMUR_POSTALIGN __attribute__ ((aligned)) is wrapped in an #ifndef WIN32. So what you need to do is define WIN32 in your Visual Studio project!
来源：https://stackoverflow.com/questions/32923135/compiling-gcc-code-in-visual-studio-causes-error-c3646-attribute-unknown