How to properly initialize array of structures inside another structure and return it from function?-CodePudding

I have an array of such structures:

typedef struct month {
    char cName[20];
    char cAbbr[20];
    int iDays;
    int iNumber;
} MONTH;

which is nested in another structure:

typedef struct input{
    MONTH * pMonths;
    DATE sDate;
    CALCS sCalcs;
} INPUT;

I initialize this array of structs in stack like that:

MONTH * init_months(bool bLeap) {

    MONTH months[NUM_MONTHS] = {
        { .cName = "January", .cAbbr = "Jan", .iDays = 31, .iNumber = 1 },
        { "February", "Feb", 28, 2 },
        { "March", "Mar", 31, 3 },
        { "April", "Apr", 30, 4 },
        { "May", "May", 31, 5 },
        { "June", "Jun", 30, 6 },
        { "July", "Jul", 31, 7 },
        { "August", "Aug", 31, 8 },
        { "September", "Sep", 30, 9 },
        { "October", "Oct", 31, 10 },
        { "November", "Nov", 30, 11 },
        { "December", "Dec", 31, 12 }
    };

    if(bLeap){
        months[1].iDays  ;
    }

    return months;
}

The question is, if i form a INPUT structure inside some function:

INPUT GetUserInput(void){

    // init months
    MONTH * pMonths;
    pMonths = init_months(isLeap(sDate.iYear));

    // some code here
    ...
    INPUT sInput = { pMonths, sDate, sCalcs };

    // return
    return sInput;
}

then how to properly initialize array of MONTH and/or how to properly initialize INPUT so it would contain valid data when returned from GetUserInput() ?

CodePudding user response：

You have 3 options:

Make it static (but all returned references will reference the same array).

    static MONTH months[NUM_MONTHS] = {

Use malloc and compound literal

    MONTH *months = malloc(sizeof(*months) * NUM_MONTHS);
    
    /* check if memory was allocated */
    
    memcpy(months, (MONTH[]){
        { .cName = "January", .cAbbr = "Jan", .iDays = 31, .iNumber = 1 },
        { "February", "Feb", 28, 2 },
        { "March", "Mar", 31, 3 },
        { "April", "Apr", 30, 4 },
        { "May", "May", 31, 5 },
        { "June", "Jun", 30, 6 },
        { "July", "Jul", 31, 7 },
        { "August", "Aug", 31, 8 },
        { "September", "Sep", 30, 9 },
        { "October", "Oct", 31, 10 },
        { "November", "Nov", 30, 11 },
        { "December", "Dec", 31, 12 }}, sizeof(*months) * NUM_MONTHS);

Wrap the table into another structure and return by value

typedef struct
{
    MONTH months[NUM_MONTHS];
}YEAR;

YEAR init_months(bool bLeap) {

    YEAR year = {{
        { .cName = "January", .cAbbr = "Jan", .iDays = 31, .iNumber = 1 },
        { "February", "Feb", 28, 2 },
        { "March", "Mar", 31, 3 },
        { "April", "Apr", 30, 4 },
        { "May", "May", 31, 5 },
        { "June", "Jun", 30, 6 },
        { "July", "Jul", 31, 7 },
        { "August", "Aug", 31, 8 },
        { "September", "Sep", 30, 9 },
        { "October", "Oct", 31, 10 },
        { "November", "Nov", 30, 11 },
        { "December", "Dec", 31, 12 }}};

    if(bLeap){
        year.months[1].iDays  ;
    }

    return year;
}