cannot malloc nfq_q_handle because of 'incomplete application error' [duplicate] - c

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'

Answer 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.

Answer 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.

Answer 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.

Answer 4

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

Answer 5

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 <stdio.h>
#include <stdint.h>
#include <string.h>
#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 <stdio.h>
#include <stdint.h>
#include <string.h>
#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" & "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" & "arrB" are constant lists and fixed before to compile. I would like to use a label(let me easy to maintenance & save RAM memory).

Answer 6

Really late to the party here, but a special case of the reasons for this error cited above would simply be to reference a structure with sizeof() above where the structure is defined:
int numElements = sizeof(myArray)/sizeof(myArray[0]);
.
.
.
myArray[] =
{
{Element1},
{Element2},
{Element3}
};