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 <stdio.h>
#include <stdlib.h>
#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",&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'  

Solution 1

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->canPlay = 1 it would be better to put the definition of the structure in header.h.

Solution 2

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.

Solution 3

Your error is also shown when trying to access the sizeof() of an non-initialized extern array:

extern int a[];
sizeof(a);
>> error: invalid application of 'sizeof' to incomplete type 'int[]'

Note that you would get an array size missing error without the extern keyword.

Comments

[ChrisWue]

Btw: stackoverflow.com/questions/605845/…

[MetallicPriest]

Have you declared struct player in header.h?

[Renan Greinert]

If header.h contains the definition of "player", this program should compile fine, both in C and C++

[captain]

In the header I just put "struct player;" I didn't like it in the beginning but when I do something like players.startinCapital=1500 I don't get an error and it prints the result without a problem. So basically I have to make a function which constructs the struct?

[ouah]

@captain put the complete declaration of the struct player type in your header.h file

[captain]

@ouah I did this an it works. What should I put inside the init_player?

[Tony Han]

I have the similar problem. And I use a 3rd-part lib, so I can't get the implementation. But I have to get the size of the struct(for passing that to other lib). How to do this?

[lc2047]

@nhahtdh Thanks for your advice. But it happens to another problem. Also, initially #ifndef is used to avoid multiple declare. Right? if not, please let me know the detail.