Invalid application of sizeof to incomplete type with a struct

Question

I have a  struct where I put all the information about the players  That s my struct   struct player     int startingCapital     int currentCapital     int startingPosition     int currentPosition     int activePlayer      int canPlay             And that s my main    include  lt stdio h gt   include  lt stdlib h gt   include  header h    int main int argc  char  argv       int s i numOfPlayers     struct player  players      printf  Give the number of players   n        scanf   d   amp numOfPlayers        players    struct player   calloc numOfPlayers sizeof struct player         system  PAUSE       return 0      I m asking the user to give the number of players and then I try to allocate the needed memory  But I m getting this compiler error that I can t figure out   invalid application of  sizeof  to incomplete type  player

User · Answer

The cause of errors such as  Invalid application of sizeof to incomplete type with a struct       is always lack of an include statement  Try to find the right library to include

User · Answer

I am a beginner and may not clear syntax  To refer above information  I still not clear         main c        Created on  15 Nov 2019       include  lt stdio h gt   include  lt stdint h gt   include  lt string h gt    include  dummy h   char arrA               0x41          0x43          0x45          0x47          0x00       define sizeA sizeof arrA   int main void        printf   r n s  arrA       printf   r nsize of    d   sizeof arrA        printf   r nsize of    d   sizeA        printf   r n s  arrB         printf   r nsize of    d   sizeof arrB        printf   r nsize of    d   sizeB         while 1        return 0            dummy c        Created on  29 Nov 2019        include  lt stdio h gt   include  lt stdint h gt   include  lt string h gt    include  dummy h    char arrB               0x42          0x44          0x45          0x48          0x00            dummy h        Created on  29 Nov 2019       ifndef DUMMY H   define DUMMY H   extern char arrB      define sizeB sizeof arrB    endif    DUMMY H      15 16 56      Incremental Build of configuration Debug for project T3      Info  Internal Builder is used for build gcc -O0 -g3 -Wall -c -fmessage-length 0 -o main o      main c   In file included from    main c 12     main c  In function  main      dummy h 13 21    error  invalid application of  sizeof  to incomplete type  char        define sizeB sizeof arrB                            main c 32 29  note  in expansion of macro  sizeB    printf   r nsize of    d   sizeB                                       15 16 57 Build Failed  1 errors  0 warnings   took 384ms    Both  arrA   amp   arrB  can be accessed  print it out   However  can t get a size of  arrB    What is a problem there    Is  char    incomplete type  or  sizeof  does not accept the extern variable  label    In my program   arrA   amp   arrB  are constant lists and fixed before to compile  I would like to use a label let me easy to maintenance  amp  save RAM memory

User · Answer

I think that the problem is that you put  ifdef instead of  ifndef at the top of your header h file

User · Answer

It means the file containing main doesn t have access to the player structure definition  i e  doesn t know what it looks like   Try including it in header h or make a constructor-like function that allocates it if it s to be an opaque object  EDIT If your goal is to hide the implementation of the structure  do this in a C file that has access to the struct  struct player   init player            struct player  p   calloc 1  sizeof  p                      return p     However if the implementation shouldn t be hidden - i e  main should legally say p- gt canPlay   1 it would be better to put the definition of the structure in header h

User · Answer

Your error is also shown when trying to access the sizeof   of an non-initialized extern array   extern int a    sizeof a    gt  gt  error  invalid application of  sizeof  to incomplete type  int      Note that you would get an array size missing error without the extern keyword

[c] Invalid application of sizeof to incomplete type with a struct

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