Initialize an empty nested struct using a function

Question

I have to initialize tCoworking coworking by implementing init_coworking function that is declared at the end.

/* Constants *********************************************************/
#define nWorkSpaces 50
#define unlimited 2000

/* Types *************************************************************/
typedef enum {tableFlex, tableFix, officeFix} rate;
typedef char string[55];

typedef struct {
    int reservationId;
    float monthPayment;
} tContractAnnex;

typedef struct {
    int id;
    string name;
    int discount;
} tPartner;

typedef struct {
    int id;
    float surface;
    rate rateType;
} tWorkspace;

typedef struct {
    int partnerId;
    int month;
    int year;
    tContractAnnex annex;
} tContract;

typedef struct {
    tWorkspace workSpace[nWorkSpaces];
    tContract contract[unlimited];
    tPartner partner[unlimited];
} tCoworking;

/* Function declaration */

void init_coworking(tCoworking *coworking);

As you can see the problem I have is that tCoworking is a nested struct with array of stucts as data types.. So far I'm doing this in order to initialize it but it must be a better way to do it.

void init_coworking(tCoworking *coworking){
coworking = malloc(sizeof(tCoworking));

 coworking->partner[0].id = 0;
 coworking->partner[0].discount = 0;
 strcpy(coworking->partner[0].name, "");
 
 coworking->workSpace[0].id = 0;
 coworking->workSpace[0].rateType = 0;
 coworking->workSpace[0].surface = 0;
 
 
 coworking->contract[0].partnerId = 0;
 coworking->contract[0].year = 0;
 coworking->contract[0].month = 0;
 coworking->contract[0].annex.monthPayment = 0;
 coworking->contract[0].annex.reservationId = 0;
}

StoneThrow · Accepted Answer · 2020-10-03 16:54:40Z

1

void init_coworking(tCoworking *coworking) {
 coworking && memset( coworking, 0, sizeof( tCoworking ) );
}

memset initializes a block of memory - of specifiable length - to a single byte value. Your example indicates that you desire zero-initialization of the entire object, so memset serves this purpose well.
NULL-check your input argument.

I recommend you not malloc or calloc in your function because your function signature implies that the caller is the owner of the tCoworking. If you malloc within your init_coworking() function, then you'll have created a new heap-allocated instance of a tCoworking with no clear ownership. You can try keep track of newly-allocated objects in some type of container, but that's going far beyond the scope of your question -- keep it simple.

edited Oct 3, 2020 at 16:54

answered Oct 3, 2020 at 16:42

StoneThrow

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Comments

4386427 · Accepted Answer · 2020-10-03 17:19:30Z

The simplest way is to use calloc. Like malloc it allocates memory for you but it also sets all the memory to zero.

However - more important is that your current function doesn't make sense. The memory you allocate is simply lost. The caller of init_coworking will never get the allocated and initialized memory.

Either you should:

Not do any malloc(or calloc)

or

Return the malloced pointer.

Since the prototype suggest that you get a tCoworking pointer, the most likely thing is that it's already allocated (in some way), i.e. you want option 1.

So just do:

void init_coworking(tCoworking *coworking){   // NO malloc
    memset(coworking, 0, sizeof(tCoworking));
}

In case you only want the first array member set to zero (like your code indicates) you may get a little performance improvement by:

void init_coworking(tCoworking *coworking){   // NO malloc
    memset(&coworking->partner[0], 0, sizeof(coworking->partner[0]));
    ... similar for the other arrays ...
}

but I doubt that's worth the trouble...

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