How to suppress unused parameter warnings in C

Question

For instance   Bool NullFunc const struct timespec  when  const char  who       return TRUE      In C   I was able to put a         comment around the parameters  But not in C of course  where it gives me the error error  parameter name omitted

User · Accepted Answer

I usually write a macro like this    define UNUSED x   void  x    You can use this macro for all your unused parameters   Note that this works on any compiler    For example   void f int x        UNUSED x

User · Answer

In MSVC to suppress a particular warning it is enough to specify the it s number to compiler as  wd   My CMakeLists txt contains such the block   If  MSVC      Set  CMAKE EXE LINKER FLAGS     CMAKE EXE LINKER FLAGS    NODEFAULTLIB  LIBCMT       Add definitions   W4  wd4512  wd4702  wd4100  wd4510  wd4355  wd4127      Add definitions   D CRT SECURE NO WARNINGS  Elseif  CMAKE COMPILER IS GNUCXX OR CMAKE COMPILER IS GNUC      Add definitions  -Wall -W -pedantic  Else        Message   Unknown compiler   Endif      Now I can not say what exactly  wd4512  wd4702  wd4100  wd4510  wd4355  wd4127 mean  because I do not pay any attention to MSVC for three years  but they suppress superpedantic warnings that does not influence the result

User · Answer

Labelling the attribute is ideal way  MACRO leads to sometime confusion  and by using void x  we are adding an overhead in processing   If not using input argument  use  void foo int   attribute    unused  key        If not using the variable defined inside the function   void foo int key       int hash   0     int bkt   attribute    unused     0      api call x  hash  bkt       Now later using the hash variable for your logic but doesn   t need bkt  define bkt as unused  otherwise compiler says bkt set bt not used    NOTE  This is just to suppress  the warning not for optimization

User · Answer

You can use gcc clang s unused attribute  however I use these macros in a header to avoid having gcc specific attributes all over the source  also having   attribute   everywhere is a bit verbose ugly    ifdef   GNUC      define UNUSED x  UNUSED     x   attribute      unused      else    define UNUSED x  UNUSED     x  endif   ifdef   GNUC      define UNUSED FUNCTION x    attribute      unused     UNUSED     x  else    define UNUSED FUNCTION x  UNUSED     x  endif   Then you can do     void foo int UNUSED bar             I prefer this because you get an error if you try use bar in the code anywhere so you can t leave the attribute in by mistake   and for functions     static void UNUSED FUNCTION foo  int bar              Note 1   As far as I know  MSVC doesn t have an equivalent to   attribute      unused       Note 2   The UNUSED macro won t work for arguments which contain parenthesis so if you have an argument like float   coords  3    you can t do float UNUSED   coords  3   or float   UNUSED coords   3   This is the only downside to the UNUSED macro I found so far  in these cases I fall back to  void coords

User · Answer

Seeing that this is marked as gcc you can use the command line switch Wno-unused-parameter   For example   gcc -Wno-unused-parameter test c   Of course this effects the whole file  and maybe project depending where you set the switch  but you don t have to change any code

User · Answer

A gcc g   specific way to suppress the unused parameter warning for a block of source code is to enclose it with the following pragma statements    pragma GCC diagnostic push  pragma GCC diagnostic ignored  -Wunused-parameter   lt code with unused parameters here gt   pragma GCC diagnostic pop

User · Answer

For the record  I like Job s answer above but I m curious about a solution just using the variable name by itself in a  do-nothing  statement   void foo int x        x     unused                Sure  this has drawbacks  for instance  without the  unused  note it looks like a mistake rather than an intentional line of code   The benefit is that no DEFINE is needed and it gets rid of the warning   Are there any performance  optimization  or other differences

User · Answer

I got the same problem  I used a third-part library  When I compile this library  the compiler  gcc clang  will complain about unused variables    Like this     test cpp 29 11  warning  variable  magic  set but not used  -Wunused-but-set-variable         short magic            test cpp 84 17  warning  unused variable  before write   -Wunused-variable             int64 t before write   Thread  currentTimeMillis      So the solution is pretty clear  Adding -Wno-unused as gcc clang CFLAG will suppress all  unused  warnings  even thought you have -Wall set   In this way  you DO NOT NEED to change any code

User · Answer

I ve seen this style being used   if  when    who    format    data    len

User · Answer

In gcc  you can label the parameter with the unused attribute      This attribute  attached to a variable  means that the variable is   meant to be possibly unused  GCC will not produce a warning for this   variable    In practice this is accomplished by putting   attribute     unused   just before the parameter  For example   void foo workerid t workerId        becomes  void foo   attribute    unused   workerid t workerId

User · Answer

With gcc with the unused attribute   int foo    attribute    unused   int bar        return 0

[c] How to suppress "unused parameter" warnings in C?

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