How do I solve the issue of multiple initialization when using malloc?

Question

I need to use malloc to allocate memory to one instance of struct game and store the return pointer in p_game_info for a game.

This is the code for the relevant function in game.c

void play_game()
{
    struct game *p_game_info = 0;
    struct game *p_game_info = malloc (sizeof (struct game));
}

This is the code for the struct in game.h

struct game
{
    char board[3][3];
    char playerNames[2][MAX_NAME_LEN];
    int status;
    boolean finished;
};

In VS I am getting the following error message

error C2374: 'p_game_info': redefinition; multiple initialization

I have been searching online for a similar problem but have been unsuccessful.

Thanks for your help.

the problem is not malloc but you declared the `p_game_info` twice in the function play_game() — Dr Deo, Apr 14 '18 at 17:44

score 1 · Answer 1 · answered Apr 14 '18 at 17:38

1

Solution is there in error message itself, don't declare & initialize every time, declare p_game_info only once.

void play_game() {
    struct game *p_game_info = malloc (sizeof (struct game));/* declaration & initialization both at a time */
}

answered Apr 14 '18 at 17:38

Achal

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score 1 · Answer 2 · answered Apr 14 '18 at 17:39

As the errors says, you are initializing the pointer twice in your function. Also, you are declaring it also twice..

try doing both only once, something like.

void play_game()
{
    struct game *p_game_info = 0;                 // declaring and initializing once
    p_game_info = malloc (sizeof (struct game));  // allotting memory.
}

Alternatively, you can combine both in one line.

void play_game()
{
    struct game *p_game_info = malloc (sizeof (struct game));
}

Alex Lop. · Answer 3 · 2018-04-14T17:51:01.430

Fix it to:

void play_game()
{
    struct game *p_game_info = 0;
    /* struct game* */ p_game_info = malloc (sizeof (struct game));
}

The error means what it actually says. You initialized (defined) twice the same variable p_game_info.

According to the standard, you may have multiple declarations, like here (which should compile perfectly)

struct game *p_game_info;
struct game *p_game_info;
struct game *p_game_info;
struct game *p_game_info = 0;
....
void play_game()
{
    p_game_info = malloc (sizeof (struct game));
}

But it must have only one definition (initialization)!

More about declaration and initialization in C is in this link: What is the difference between a definition and a declaration?

EDIT

As noticed by Weather Vane, the example of multiple declarations, is OK only at a file scope - and is called a "tentative declaration"

You can only do this at file scope - and is called a "tentative declaration". — Weather Vane, Apr 14 '18 at 17:45
@WeatherVane You are right, I'll move it out of the function scope. — Alex Lop., Apr 14 '18 at 17:47

How do I solve the issue of multiple initialization when using malloc?

3 Answers3