Error: Expected expression before structure

Question

I am trying to return a pointer to a structure but I keep getting this weird error bboard.c:35: error: Expecte expression before 'BBoard' Does anyone have any ideas on to what could be causing this. I fairly new in c so my apologies of this is a trivial question.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "bboard.h"

struct BBoard {
int create[MAX_ROWS][MAX_COLS];
};


BBoard * bb_create(int nrows, int ncols){
int i,j;
srand(time(NULL));
struct BBoard Bboard;
for (i = 0; i < nrows; i++){
    for (j = 0; j < ncols; j++){
        int r = rand() % 4;
        //printf("%d",r);

        if( r == 0){ 
        Bboard.create[i][j] = 1;}
        if(r == 1){
        Bboard.create[i][j] = 2;}
        if(r == 2){ 
        Bboard.create[i][j] = 3;}
        if(r == 3){
        Bboard.create[i][j] = 4;}
        printf(" %d ",Bboard.create[i][j]);
            }
        printf("\n");
        }
struct BBoard *boardPtr = malloc(sizeof(struct BBoard));
if (boardPtr != NULL){
//printf("%d",boardPtr->create[1][1]);
return BBoard *boardPtr;
}
else{
printf("Error");
}
}

/**extern void bb_display(BBoard *b){
int i,j;
BBoard Bboard = b;
for (i = 0; i < 5; i++){
    for (j = 0; j < 5; j++){
        printf("%d",Bboard.create[i][j]);
        }
    }
}**/


int main(){
BBoard *bptr;
bptr = bb_create(5,5);
//printf("%d",bptr->create[0][1]);
}

Answer 1

In C, you need to use struct BBoard until you've used:

typedef struct BBoard BBoard;

In C++, you don't need to create the typedef.

---

Could you elaborate a litle bit? I dont understand.

You have:

struct BBoard
{
    int create[MAX_ROWS][MAX_COLS];
};


BBoard * bb_create(int nrows, int ncols)
{
    …

The structure definition creates a type struct BBoard. It does not create a type BBoard; it only creates struct BBoard. So, when you next write BBoard *bb_create, there isn't a type BBoard, so the compiler complains.

If you write one of these sequences — either:

typedef struct BBoard
{
    int create[MAX_ROWS][MAX_COLS];
} BBoard;

or:

typedef struct BBoard BBoard;
struct BBoard
{
    int create[MAX_ROWS][MAX_COLS];
};

or:

struct BBoard
{
    int create[MAX_ROWS][MAX_COLS];
};
typedef struct BBoard BBoard;

then you both define a type struct BBoard and an alias for the type BBoard and then your code will compile.

In C++, simply defining a struct or class defines a type which can be used without the struct or class prefix.

---

If your code compiled past the start of the function definition, then (a) you aren't using a standard C compiler, and (b) you have problems further down your code at:

return BBoard *boardPtr;

Since this is part of:

    struct BBoard *boardPtr = malloc(sizeof(struct BBoard));
    if (boardPtr != NULL){
        //printf("%d",boardPtr->create[1][1]);
        return BBoard *boardPtr;
    }
    else{
        printf("Error");
    }
}

You really don't need to cast the return type at all, but if you think you do, you should use proper cast notation (one of these two, preferably the first):

        return boardPtr;
        return (BBoard *)boardPtr;

The error message in the else clause should be more informative, should end with a new line, should be written to standard error, and should be followed by a return 0; or equivalent.