Need help calling function from header file

Question

I have a header file called "ChessMoves.h" and a c file call ChessMoves with a bunch of different functions.

Header file

#ifndef __CHESSMOVES_H
#define __CHESSMOVES_H

typedef struct Location
{
    // the square's column ('a' through 'h')
    char col;

    // the square's row (1 through 8)
    int row;
} Location;

typedef struct Move
{
    // location where this piece is moving from
    Location from_loc;

    // location where this piece is moving to
    Location to_loc;

    // what type of chess piece is being moved
    char piece;

    // whether this move captures another piece
    short int isCapture;

    // the color of the piece being moved
    Color color;
} Move;

File I'm calling to

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "ChessMoves.h"

void parseNotationString(char *str, Move *whiteMove, Move *blackMove){

    int i, space = 0, j = 0, k = 0, l = 0;
    int white[10], black[10], move[10], to[2];

    whiteMove.color = WHITE;
    if(white[0] > 64)
        whiteMove.piece = white[0];
    if(white[0] < 64)
        whiteMove.from_loc.row = white[0];
    for(i = 0; i < 10; i++)
        if(white[i] == 'x')
            whiteMove.isCapture = 1;
    for(i = 0; j < 10; i++)
        if(white[i] == ' ')
            to[0] = white[i-2];
            to[1] = white[i-1];

    printf("%c %c", to[0], to[0]);
}

We were given a file to test the code and in that file he has:

whiteMove.color != WHITE

and if whiteMove.color does not equal WHITE it will display "FAIL" so I tried setting

whiteMove.color = WHITE

but I keep getting "request for member 'color' in something not a structure or union. The same thing goes for the other structs I try to call. I tried making it,

Move.color = WHITE

and that doesn't work either.

whiteMove.color = WHITE; should be whiteMove->color; It's a pointer. — bmargulies
– bmargulies, Commented Sep 25, 2016 at 15:43
Since whiteMove and blackMove are both pointers, you need to either use the -> operator (whiteMove->color) or dereference the pointer before applying the . operator ((*blackMove).color). — John Bode
– John Bode, Commented Sep 25, 2016 at 15:44
You have a bug in that last if statement. And now you know why braces are good style. :) — Schwern
– Schwern, Commented Sep 25, 2016 at 17:36

Community · Accepted Answer · 2017-04-12 07:32:04Z

So we can have something that compiles I've put this all into a file, chopped off the irrelevant bits, and added the missing Color enum.

$ cat test.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef enum { WHITE, BLACK } Color;

typedef struct Location
{
    // the square's column ('a' through 'h')
    char col;

    // the square's row (1 through 8)
    int row;
} Location;

typedef struct Move
{
    // location where this piece is moving from
    Location from_loc;

    // location where this piece is moving to
    Location to_loc;

    // what type of chess piece is being moved
    char piece;

    // whether this move captures another piece
    short int isCapture;

    // the color of the piece being moved
    Color color;
} Move;


void parseNotationString(char *str, Move *whiteMove, Move *blackMove){

    int i, space = 0, j = 0, k = 0, l = 0;
    int white[10], black[10], move[10], to[2];

    whiteMove.color = WHITE;

    if(white[0]>64)
        whiteMove.piece = white[0];
    if(white[0]<64)
        whiteMove.from_loc.row = white[0];
    for(i=0;i<10;i++)
        if(white[i] == 'x')
            whiteMove.isCapture = 1;
    for(i=0;j<10;i++)
        if(white[i] == ' ')
            to[0] = white[i-2];
            to[1] = white[i-1];

    printf("%c %c", to[0], to[0]);
}

Compiling it with clang gives the answer immediately.

$ make
cc -Wall -g    test.c   -o test
test.c:40:14: error: member reference type 'Move *' (aka 'struct Move *') is a pointer; did you mean
      to use '->'?
    whiteMove.color = WHITE;
    ~~~~~~~~~^
             ->
test.c:43:18: error: member reference type 'Move *' (aka 'struct Move *') is a pointer; did you mean
      to use '->'?
        whiteMove.piece = white[0];
        ~~~~~~~~~^
                 ->
test.c:45:18: error: member reference type 'Move *' (aka 'struct Move *') is a pointer; did you mean
      to use '->'?
        whiteMove.from_loc.row = white[0];
        ~~~~~~~~~^
                 ->
test.c:48:22: error: member reference type 'Move *' (aka 'struct Move *') is a pointer; did you mean
      to use '->'?
            whiteMove.isCapture = 1;
            ~~~~~~~~~^
                     ->
4 errors generated.
make: *** [test] Error 1

whiteMove is a Move *, a pointer to a Move structure. As such it has to be dereferenced with ->. . is for direct access.

clang's error messages are excellent and even give you a suggestion how to fix it. I would strongly suggest you use it, or compiler with similarly good errors, while learning C.

Furthermore your code has a subtle bug.

    for(i=0;j<10;i++)
        if(white[i] == ' ')
            to[0] = white[i-2];
            to[1] = white[i-1];

This does not do what the indentation says it does. It's actually this.

    for(i=0;j<10;i++)
        if(white[i] == ' ')
            to[0] = white[i-2];

    to[1] = white[i-1];

And this is why we always use braces.

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