UBound

Syntax:

    output = UBound( array_name )

Command Availability:

Available on all microcontrollers. From build 1644.

Explanation:

The UBound function returns the number of elements declared for an array, exactly as written in its Dim statement. Because an array’s size is fixed at compile time, UBound is resolved entirely by the compiler — the call is replaced with a plain numeric constant before the program is assembled. It costs no RAM and no runtime instructions to use. 

    Dim Buffer(512) As Byte
    Dim BufferSize As Word

    BufferSize = UBound(Buffer)          ' <<< resolves to the literal 512

Key line: UBound(Buffer) — compiles directly to the constant 512; nothing is read from memory at runtime.

This replaces the older workaround of maintaining a separate #Define constant purely to remember an array’s size: 

    Dim MySensorReadings(10) As Word

    For i = 1 to UBound(MySensorReadings)
        MySensorReadings(i) = 0
    Next

Key line: UBound(MySensorReadings) — always matches the array’s actual declared size, even if the Dim line above it is edited later, because it reads the size from the declaration itself rather than from a second, hand-maintained constant that could drift out of sync.

UBound also works on a fixed-length String variable, returning its declared maximum length in characters — see Dim for why strings and arrays share this size mechanism internally. 

    Dim Greeting As String * 20
    Dim MaxChars As Byte

    MaxChars = UBound(Greeting)          ' <<< resolves to the literal 20

Constraint: UBound only accepts the name of an array or a String variable. Using it on a plain scalar variable (a Byte, Word, etc. that was not declared with array brackets) raises a compile-time error, since a scalar has no declared element count to return.

See Also:

  • Arrays — declaring arrays, and how element 0 is used (or not used)
  • Dim — declaring arrays and strings
  • Len — the runtime length of a string’s current contents, as opposed to its declared maximum size
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