Array Size Problem

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October 22nd, 2010, 07:20 AM

andy101

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Array Size Problem

From a database I get a collection of character arrays of different sizes. I need to process some of these arrays and to do this I need to be able to determine the size of each array.
If this cannot be done then I may need to export out of the database a series of defines, one for each array. This is more work, do I need to do this or can I find out the size?

Sample code of problem below:-

Code:

char *OPTIONS1[4] = {"OPT_1", "OPT_2", "OPT_3", "OPT_4"};
char *OPTIONS2[2] = {"OPT_1", "OPT_4"};
char *OPTIONS3[1] = {"OPT_1234"};
 
char* GetOptions(short enumValue, char** szOptions)
{
	int i, nOptions;
	short size;
	nOptions = 1;
	size = HOW TO DETERMINE THE SIZE OF ARRAY szOptions !!!!!!!!!
	
	printf("Array Size = %d\n", size);
	for(i = 0; i < size; i++)
	{
    	// do something with OPTIONS[j]
    	...
    	...
    }
    return szResult;
}

// In the Main program call GetOptions() for 3 different sized arrays
option = GetOptions(1, OPTIONS1);
option = GetOptions(2, OPTIONS2);
option = GetOptions(3, OPTIONS3);

October 22nd, 2010, 07:27 AM

mitakeet

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Your question is database and database interface specific, not really related to C/C++. You should try a database forum.

Having said that, basic arrays in C/C++ always lack any notion of their size and the size MUST be supplied by the code that creates/fills the array. I am certain that that facility is available in the access library you are using.

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October 22nd, 2010, 07:40 AM

ptr2void

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If your arrays are truly created at compile time, you can use:

Code:

sizeof(OPTIONS1)/sizeof(*OPTIONS1)

to determine the size of the array to be passed to the function. It must be passed to the function however, as that will not work inside the function. Also, if the above is true, your arrays should be declared as const char *:

Code:

const char *OPTIONS1[4] = {"OPT_1", "OPT_2", "OPT_3", "OPT_4"};
const char *OPTIONS2[2] = {"OPT_1", "OPT_4"};
const char *OPTIONS3[1] = {"OPT_1234"};

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October 22nd, 2010, 07:59 AM

mitakeet

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I thought you were asking how to know how many elements were returned in an array from a database call. For data in a program you can use a 'trick' where you have some gate value as the last element of the array. For instance:

Code:

const char *OPTIONS1[4] = {"OPT_1", "OPT_2", "OPT_3", "OPT_4", NULL};
for (int i=0; OPTIONS[i] != NULL; ++i){
    ...do something
}

will work. However this 'trick' is not very reliable in integer/float arrays unless you can know with absolute certainty that a given value will never be represented in the data. This does work quite well in pointer arrays as NULL is indeed guaranteed to be an invalid value for a pointer.

October 22nd, 2010, 08:00 AM

andy101

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Quote:

Originally Posted by mitakeet

This is a striaight c-code question, the export from the database generates the following arrays (I will make them const) as ptr2void suggested.

Code:

const char *OPTIONS1[4] = {"OPT_1", "OPT_2", "OPT_3", "OPT_4"};
const char *OPTIONS2[2] = {"OPT_1", "OPT_4"};
const char *OPTIONS3[1] = {"OPT_1234"};

Perhaps I need to do the following:-

Code:

const char *OPTIONS1[5] = {"OPT_1", "OPT_2", "OPT_3", "OPT_4", ""};
const char *OPTIONS2[3] = {"OPT_1", "OPT_4", ""};
const char *OPTIONS3[1] = {"OPT_1234", ""};

Not sure if the last item is best suited to "".

Then I could test for OPTIONS1[5] != NULL

Any comments?

October 22nd, 2010, 08:31 AM

mitakeet

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You could do while (strlen(OPTIONS[i]) > 0)..., but NULL is the more commonly accepted approach.

If you are not stuck with C, go ahead and use vectors. Vectors always know their size.

October 22nd, 2010, 04:33 PM

LittleGrin

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Quote:

Originally Posted by mitakeet

You could do while (strlen(OPTIONS[i]) > 0)..., but NULL is the more commonly accepted approach.

strlen(OPTIONS[i]) gives undefined behavior if OPTIONS[i] is NULL, which - if the end of the OPTIONS array is reached - is the case here.

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Array Size Problem

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