Iterate through a C array

Question

I have an array of structs that I created somewhere in my program   Later  I want to iterate through that  but I don t have the size of the array   How can I iterate through the elements  Or do I need to store the size somewhere

User · Answer

If the size of the array is known at compile time, you can use the structure size to determine the number of elements.

struct foo fooarr[10];

for(i = 0; i < sizeof(fooarr) / sizeof(struct foo); i++)
{
  do_something(fooarr[i].data);
}

If it is not known at compile time, you will need to store a size somewhere or create a special terminator value at the end of the array.

User · Answer

It depends  If it s a dynamically allocated array  that is  you created it calling malloc  then as others suggest you must either save the size of the array number of elements somewhere or have a sentinel  a struct with a special value  that will be the last one    If it s a static array  you can sizeof it s size the size of one element  For example   int array 10   array size      array size   sizeof array  sizeof int     Note that  unless it s global  this only works in the scope where you initialized the array  because if you past it to another function it gets decayed to a pointer   Hope it helps

User · Answer

You can store the size somewhere  or you can have a struct with a special value set that you use as a sentinel  the same way that   0  indicates the end of a string

User · Answer

I think you should store the size somewhere    The null-terminated-string kind of model for determining array length is a bad idea  For instance  getting the size of the array will be O N  when it could very easily have been O 1  otherwise   Having that said  a good solution might be glib s Arrays  they have the added advantage of expanding automatically if you need to add more items   P S  to be completely honest  I haven t used much of glib  but I think it s a  very  reputable library

[c] Iterate through a C array

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