Common GCC__ attribute__

When I study brpc. Browse the code , View many “ __attribute__ Used places ”.

I'm thinking about what to use under what circumstances “ __attribute__”？ Use it properly __attribute Coding can improve the efficiency of the program . According to my investigation , Here are some examples .

• __attribute __(noinline)： Prevent thinking about inlining functions
• __attribute __(packed)： Specifies that each member of a structure or union is placed to minimize the memory required . The packed Property specifies that structure members should have the smallest possible alignment
• __attribute __(unused)： Informs the compiler that you expect variables to be unused , And tell it not to give a warning if you don't use it
• __attribute __(weak)： Define library functions that can be overridden in user code
• __attribute __(format)： from printf Use and point out what args With format
• __ attribute __(const)： This function does not read or modify any global memory
• __attribute __(aligned(X))： Increase the alignment of structures or structure members . Minimum alignment , In bytes . You cannot use this property to reduce the alignment of functions , You can only increase its alignment .
• __attribute __(unused)： This attribute attached to a variable means that the variable may not be used .GCC No warning will be issued for this variable .
• __attribute __(always_inline)： Usually , Unless optimization is specified , Otherwise, the function will not be inlined . For inline declared functions , Even if the optimization level is not specified , This property will also inline functions .
• __attribute __(deprecated)： If you use this variable anywhere in the source file , This attribute will generate a warning .