return value of malloc

Question

Hey

I have the following code parts:

typedef struct Board* BoardP;

typedef struct Board {
    int _rows;
    int _cols;
    char *_board;

} Board;

char* static allocateBoard(BoardP boardP, int row, int col) {

    boardP->_rows = row;
    boardP->_cols = col;
    boardP->_board = malloc(row * col * sizeof(char));

    return boardP->_board;
}

i can't seem to figure out why it gives the error expected identifier or ‘(’ before ‘static’ it gives the error after i changed return type to be char*. when it was void no error was given.

and one more question: i was taught that cast is needed when using malloc, however, this seems to be working ok without a cast. is it needed in this case?

thanks

Answer 1

Change your function to

static char* allocateBoard(BoardP boardP, int row, int col):

The return value of malloc is a void*, and in C (unlike C++), a void* is implicittly convertible to any other pointer type - except function pointers. so you don't need a cast.

Answer 2

Your function prototype needs to be:

static char* allocateBoard(BoardP boardP, int row, int col)

No cast is needed on malloc() in C; however, it is in C++.

Answer 3

In C, Casting for malloc is needed before ANSI C, as there was no void* type (perhaps as extension on some C compilers), but after ANSI C there is no need for casting at all, if you do that then you are suppressing some useful diagnostics by the compiler which is more harmful to your program. Never do casting on malloc() in C.

Answer 4

Although the casting here in this case works for you. It is suggested that you make it a habit to cast things, before you try to assign them to a different type. It saves a lot of pain later. Also when incorporating this code into C++ it saves a lot of time.