CODEWITHSUNDEEP
carraysnullstrlen
Waseem
Waseem

Reputation: 1408

How to know whether an array is initialized in C

How to know whether an array is initialized in C ? Functions like strlen() are not helping me as I dont want to know whether the array is empty or not.

Upvotes: 1

Views: 10317

Answers (2)

RedComet
RedComet

Reputation: 1202

You can't by using programmatic language features.

But you can by design and discipline. At declaration time set your array as a pointer to NULL. Then make a function to assign both memory and value to your pointer and a corresponding freeing function to destroy it when is not needed anymore, setting it to NULL again. And then making every function that processes check for NULL as an error condition.

To do bounds recognition, set the last element to NULL.

Example:

char* myArray=NULL;

/* other code */

myArray = createMyArray(n_elements);
memset(myArray,0,sizeof(int)*n_elements); /* Set the allocated memory to zero */

/* other code */

myArray[0]=functionReturningAString();
myArray[n_elements-1]=functionReturningAnotherString();

/* other code */

/*Processing*/
char* incr=myArray;
while( incr != NULL){
   processArray(incr);
   incr++;/* Increments by size of char pointer to the next pointer*/
}
free_Array(&myArray);/* this function calls free() and sets myArray to NULL*/

This is usable, when you need a lot of efficiency. Otherwise you should either create your own arraylist or use an existing library which provides it.

You need too much discipline to keep track of every possible error condition, so it can be tiresome.

Usually is just better to just use a library which provides arraylist, linkedlist, HashSets, etc. For C I use a lot of Glib functions for this.

Upvotes: 2

hmakholm left over Monica
hmakholm left over Monica

Reputation: 23332

There's no way to test that at runtime -- an uninitialized array looks just like one that has been initialized with garbage.

Depending on what you're doing, you need either to make sure the array is actually initialized or explicitly pass around a flag that tells you whether the values in the array are meaningful yet.

Also note that "whether the array is empty" is not a very meaningful concept in C. The array is just there, and it always contains whatever number of bits are necessary to represent the elements it's declared to have. Those bits may not have meaningful values, but the're always there.

Upvotes: 5

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