"Illegal Function Call" Using Asc with Uninitialized String

If you try to use the Asc function on a string that has been initialized to a value of null (""), you will correctly receive an "Illegal function call" error message. The string must be assigned to a value other than "" (the null string) for the Asc function to return the ASCII value of the first character in the string.

This information is documented in the QB.EXE 4.5 or QBX.EXE 7.0/7.1 online Help for the Asc function, but is not available when the error message is received when the Help option is chosen. Below are two code examples that reproduce the error. By assigning the string to any value, the Asc function works without error.

The following code examples will fail:

Code Error Example 1

Code Error Example 2

The following code examples will work correctly:

Correct Code Example 1

Output: 32

Correct Code Example 2

Output: 80

To work around the error, check the length of the string with the Len function in an IF...THEN statement to ensure it is greater than zero before passing the string as an argument to the Asc function. The following code example demonstrates the workaround. The code allows you to only use the Asc function when something has been assigned to the string, otherwise it sets the Asc value to zero. Assigning Temp$ to CHR$(0) returns a 0, but assigning it "" gives you an "Illegal function call".