Concatenation

Syntax:

    stringvar = variable1 + variable2

Command Availability:

Available on all microcontrollers.

Explanation:

The + operator joins two variables into another variable when used between strings.

This operation does not change the existing strings; it returns a new string containing the text of the joined variables — see the concatenation constraint below.

Concatenation joins the elements of the specified values, with no separator inserted between them.

Warning

Using concatenation as a parameter to commands like HSerPrint or Print, the compiler will create a system string variable to hold the result.  For example, concatenating two string constants like HSerPrint ("123"+"456") may yield incorrect results.  Use the constant SYSDEFAULTCONCATSTRING to resolve this.  Without SYSDEFAULTCONCATSTRING, there is a risk that the compiler does not allocate sufficient RAM to hold the concatenated string.   The resulting string may be corrupted, since the size of the system string variable is not sufficient.  Use SYSDEFAULTCONCATSTRING within the source program to resolve this.

Setting a Specific Size for the Compiler-Created System String Variable

Use the following to set the size of the system string variable used during concatenation.  

The compiler creates system string variables when you concatenate on a command line such as HSerPrint, Print, and many other commands.   Concatenating directly within a command is bad practice: it uses a lot of RAM and may create a number of system string variables.   It is recommended to define a string of a known length, concatenate using an assignment, and then use the resulting string.  

To control the size of the system string variable, use the following. Also use this constant to set the size when the compiler does not otherwise create a system string variable.   

    'Define the constant to control the size of system-created string variables called SYSSTRINGPARAM1, SYSSTRINGPARAM2, etc.
    Use #DEFINE  SYSDEFAULTCONCATSTRING  4          ' <<< the constant that fixes the concatenation-buffer sizing issue

    'Then, use
    HSerPrint "A"+"123"   'will print A123. Without the SYSDEFAULTCONCATSTRING constant, some microcontrollers may corrupt the result of the concatenation.

Key line: #DEFINE SYSDEFAULTCONCATSTRING 4 — reserves a system string buffer large enough for the concatenated result, preventing the corruption that can occur when the compiler under-allocates RAM for an in-line concatenation.

This concatenation constraint does not apply when concatenation is used as a plain assignment.  

Example 1:

    timevariable = 999
    stringvar = "Time = " + str(timevariable) ' Convert timevariable to a String.  This operation returns Time = 999

Example 2:

An example showing how to set a string to an escape sequence for an ANSI terminal.&#160;&#160;You can `Dim`ension a string and then assign the elements like an array. {empty} + {empty} + 

    dim line2 as string
    line2 =  27, "[", "2", "H", 27, "[","K"
    HSerPrint line2

This sends the following to the terminal: <esc>[2H<esc>[K

Example 3: Assigning a Concatenated String to the Same String

For reliable code, do not assign a string concatenation back to its own source variable.  Assign the result of a string concatenation to a different string variable instead.  To resolve, see below: 

    Dim outstring, tmpstring as string * 16
    Dim outnumber as byte

    outnumber = 24
    outstring = "Result = "
    'This concatenation may yield an incorrect string on 10f, 12f or 16f chips
    outstring = outstring + str(outnumber)          ' <<< the unreliable pattern -- assigning a concatenation back onto itself
    HserPrintCRLF 2
    HSerPrint outstring
    HserPrintCRLF 2

    outstring = "Result = "
    'This concatenation will yield the correct string, with tmpstring containing the correct concatenated string
    tmpstring = outstring +str(outnumber)          ' <<< the reliable pattern -- assigning the concatenation to a different string
    HSerPrint tmpstring
    HserPrintCRLF 2
    end

Key line: tmpstring = outstring +str(outnumber) — assigns the concatenation result to a separate string variable (tmpstring), avoiding the unreliable self-assignment shown just above it.

See Also:

  • Asc — related command in the same category
  • Str — converting a number to a string before concatenating it
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