How do I check strings that have only alphanumeric characters?
When you say alphanumeric, I assume you mean that the characters are in one of the following domains: A to Z, a to z, or 0 to 9.
There is a VFP function called IsAlpha that accepts a string and returns .T. if the first character in the string is alphabetic (A to Z, a to z). Another VFP function called IsDigit accepts a string and returns .T. if the first character in the string is numeric (0 to 9).
To check for alpha and numeric, you will need to iterate through the string checking each character with both IsAlpha and IsDigit. Here is a code sample that does what you require:
?CheckAlphaNumeric("AB3") && returns .T.
?CheckAlphaNumeric("AB@") && returns .F.
llSuccess = .F. && Empty string will return .F. from this code
FOR lnCharacter = 1 TO LENC(tcString)
lcChar = SUBSTRC(tcString,lnCharacter,1)
llSuccess = ISALPHA(lcChar) OR ISDIGIT(lcChar)