Invalid application of sizeof to incomplete type with a struct


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");

    players = (struct player *)calloc(numOfPlayers,sizeof(struct player));

  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'  

This question is tagged with c struct calloc

~ Asked on 2012-01-18 18:18:56

The Best Answer is


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.


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 *
    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.

~ Answered on 2012-01-18 18:20:17


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.

~ Answered on 2014-04-26 08:53:26

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