VFP Coding Conventions

Naming Conventions

Database Field Prefixes (CRITICAL!)

Variable Prefixes

Function Prefixes

Code Patterns

1. VFP Does NOT Have ELSEIF!

*-- CORRECT - Use DO CASE
DO CASE
CASE nResult > 0
    RETURN .T.
CASE nResult = 0
    RETURN .T.
OTHERWISE
    RETURN .F.
ENDCASE

*-- WRONG - VFP has no ELSEIF!
IF nResult > 0
    RETURN .T.
ELSEIF nResult = 0   && COMPILE ERROR!
    RETURN .T.
ENDIF

2. SCATTER for Read, REPLACE for Write (NOT GATHER!)

*-- CORRECT - Scatter to read, REPLACE to write specific fields
SELECT clients
Scatter Memvar
m.cname = "New Name"
REPLACE cname WITH m.cname
TABLEUPDATE(.T.)

*-- WRONG - Gather sends ALL fields (risky!)
Scatter Memvar
m.cname = "New Name"
Gather Memvar  && May overwrite fields you didn't intend to change!

3. File Operations - Use STRTOFILE

*-- CORRECT - STRTOFILE for append
=STRTOFILE(lcText + CHR(13)+CHR(10), lcFile, .T.)

*-- WRONG - Fopen/Fputs/Fclose is fragile
lnHandle = Fopen(lcFile)
=Fputs(lnHandle, lcText)
=Fclose(lnHandle)

4. NULL Handling

*-- CORRECT - Check type before comparison
IF VARTYPE(ddeadline) = 'D' AND ddeadline < DATE()
    lcStatus = "Overdue"
ENDIF

*-- WRONG - Will crash if field is NULL
IF ddeadline < DATE()  && Error if NULL!
    lcStatus = "Overdue"
ENDIF

5. Date Comparisons for "Overdue"

*-- CORRECT - < for strictly overdue (excludes today)
IIF(ddeadline < DATE(), "OVERDUE", "OK")

*-- WRONG - <= includes today (not overdue yet!)
IIF(ddeadline <= DATE(), "OVERDUE", "OK")

6. Error Handling with TRY/CATCH

TRY
    *-- Risky operation
    USE sometable EXCLUSIVE
    *-- Process data
CATCH TO loEx
    *-- Handle error
    log_error(loEx.Message + " in " + loEx.Procedure)
    MESSAGEBOX("Error: " + loEx.Message, 16, "Error")
FINALLY
    *-- Cleanup (always runs)
    USE IN SELECT("sometable")
ENDTRY

7. Safe Object Property Access

*-- CORRECT - Check object exists first
IF VARTYPE(loObject) = 'O' AND !ISNULL(loObject)
    lcValue = loObject.Property
ENDIF

*-- WRONG - Will crash if object is NULL or doesn't exist
lcValue = loObject.Property

Common Errors

Best Practices

1. Always use m. prefix with SCATTER MEMVAR variables
2. Prefer local variables (lc*, ln*) over public (gl_*)
3. Close cursors explicitly - don't rely on scope cleanup
4. Use TABLEUPDATE() after modifying buffered cursors
5. Handle NULL values explicitly in comparisons
6. Use TRY/CATCH for operations that might fail
7. Log errors to help with debugging

Quick Reference

*-- String functions
ALLTRIM(string)      && Remove leading/trailing spaces
UPPER(string)        && Convert to uppercase
SUBSTR(string,n,m)   && Extract substring
AT(search, string)   && Find position

*-- Date functions
DATE()               && Current date
DATETIME()           && Current datetime
DTOC(date)           && Date to character
CTOD(string)         && Character to date
DTOS(date)           && Date to string (YYYYMMDD)

*-- Type checking
VARTYPE(var)         && Returns type letter (C,N,D,L,O,U,X)
TYPE("var")          && Returns type (evaluates expression)
ISNULL(var)          && Check if NULL
EMPTY(var)           && Check if empty

*-- Array functions
ALINES(array, string, .T., CHR(13)+CHR(10))  && Split string to array
ALEN(array, 1)       && Number of rows
ASCAN(array, value)  && Find value in array

Resources

• VFPX Community
• VFP Language Reference
• FoxBin2Prg - Version control for VFP