How to check if empty array in C

Question

I have the following code in C:

int i = 0;
char delims[] = " \n";
char *result = NULL;
char * results[10];
result = strtok( cmdStr, delims );
while( result != NULL )
{
     results[i] = result;
     i++;
     result = strtok(NULL, " \n");
}

if(!results[1])
{
    printf("Please insert the second parameter...\n");
}
else
{
    ...
}

It always executes the else condition even if the results[1] is empty.

I've tried with results[1] == NULL but no success.

How do I can check if it is empty or not?

Best way to check if a character array is empty

ljedrz
– ljedrz

2012-12-13 22:32:56 +00:00
Commented Dec 13, 2012 at 22:32 — ljedrz
– ljedrz, Commented Dec 13, 2012 at 22:32

hmjd · Accepted Answer · 2012-12-13 22:32:54Z

14

Initialize the results array so all elements are NULL:

char* results[10] = { NULL };

In the posted code the elements are unitialized and will be holding random values.

Additionally, prevent going beyond the bounds of the results array:

while (i < 10 && result)
{
}

answered Dec 13, 2012 at 22:32

hmjd

122k21 gold badges216 silver badges259 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

mazunki Over a year ago

Is it correct to assume = { NULL } will set all indexes 0 to 9 to NULL? What if you want to set indexes 0 to 3 with some specific values, and fill the rest with NULL? Could I do something like = { 0, 2, 3, 4, NULL }, expecting it to fill the rest with the last element in the list?

Spiros Gkogkas Over a year ago

@mazunki It's correct to assume that array will be initialized from 0 to 9 as NULL and for your example initializing an array as array[10] = {0,1,2,3,4} the rest of the elements from 5 to 9 will initialize as NULL. You do not really need to specify NULL at the 4 index.

AnT stands with Russia · Accepted Answer · 2012-12-13 22:42:27Z

9

There's no such thing as an "empty array" or an "empty element" in C. The array always holds a fixed pre-determined number of elements and each element always holds some value.

The only way to introduce the concept of an "empty" element is to implement it yourself. You have to decide which element value will be reserved to be used as "empty value". Then you'll have to initialize your array elements with this value. Later you will compare the elements against that "empty" value to see whether they are... well, empty.

In your case the array in question consist of pointers. In this case selecting the null pointer value as the reserved value designating an "empty" element is an obvious good choice. Declare your results array as

char * results[10] = { 0 }; // or `= { NULL };`

an later check the elements as

if (results[i] == NULL) // or `if (!results[i])`
  /* Empty element */

answered Dec 13, 2012 at 22:42

AnT stands with Russia

323k44 gold badges548 silver badges793 bronze badges

1 Comment

dud3 Over a year ago

Can we check if the array is empty if we don't initialize it? int arr[10];.

Collectives™ on Stack Overflow

How to check if empty array in C

2 Answers 2

2 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related