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I have this struct:

typedef struct
{
    char name[3];
    int month_num;
    int day_num;
    int day_size; // amount of days that are field in with tasks.
    char *task[40];
}

month; // each month contains a name, its num in the calendar and days.

and I need to assign memory allocation for it. I was able to assign the memory for the struct itself:

mon = (month*)malloc(12 * sizeof(month));

But I am having trouble to do it the same for the char *task[40].

I tried a lot of possibilities, but non of them worked...

char temptask[40];
mon->task=malloc(strlen(temptask)+1);
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11
  • 3
    Standard Warning : Please do not cast the return value of malloc(). Commented Jan 28, 2015 at 8:23
  • 1
    You should malloc() for mon->task[0] and/or other elements not mon->task. Commented Jan 28, 2015 at 8:23
  • 1
    @lili No, not "what type is it inside?" but "what type is it?" Commented Jan 28, 2015 at 8:43
  • 1
    int i; <- now i is an integer. month m; <- now m.task is what? (I'm testing your understanding; this is not part of an answer) Commented Jan 28, 2015 at 8:46
  • 3
    @lil A value in C can't be "a string" and "an array of pointers" at the same time, they are not the same. Commented Jan 28, 2015 at 8:56

3 Answers 3

Reset to default
1 
for(i=0;i<40;i++)
{ 
  /* Allocating memory to each pointers and later you write to this location */
  mon->task[i] = malloc(size);/* If you have a initialized string then size = strlen(tempTask) + 1 */
}

What you have is array of pointers and just access them and allocate memory to each of the pointers individually as shown above.

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6 Comments

i have tried that option but for some reason the compailer screms: "="- cannot convert from 'void *' to 'char *'
What compiler are you using that can't convert from void* to char*? See stackoverflow.com/questions/605845/…
@JohnZwinck Sounds like a C++ compiler to me. :(
@unwind You should be right. The most acclaimed answer of yours not to cast malloc() answers the OP's question :)
@lili: If you're using a C++ compiler you need to cast the result of malloc, like (char*)malloc(...).
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char *task[40]; is an array of 40 pointers. You probably want a single array of 40 characters, in which case no need to malloc it separately, or else a single pointer in which case you can malloc(40). You can't call strlen() on an uninitialized C string, that's undefined behavior (buffer overrun).

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I think, what you need is 

char *task;

and then allocate memory as

mon[j].task=malloc(sizeof(temptask));

Next, as you've allocated memory to mon as 

 mon = malloc(12 * sizeof(month));

the access should be made as

 mon[j].task  // j being the index, running from 0 to 11

Otherwise, if you really have a char *task[40];, that means, an array of 40 char *s, then you have to allocate memory for each of them, one by one.

int p = strlen(temptask);
for(i=0;i<40;i++)
{
      mon[j].task[i] = malloc(p+1);
}
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7 Comments

What you're proposing is undefined behavior!
@JohnZwinck I really appreciate leaving the comment along with the downvote. Can you please elaborate a bit, as i'm not clear on the reason behind undefined behaviour here.
It's undefined behavior to call strlen(temptask) when temptask is an uninitialized C string. This UB was in the OP as well. There's no need for the temptask variable at all.
why do i need to write mon[i] if month are going to max 12? why is going from 0 to 39?
@JohnZwinck Is it better now?
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