26 Doing Data
Validation with
Technique Classes
Save Time By
Understanding data validation with classes
Creating a data-validation class
Testing your class
Data validation is one of the most basic and pervasive functions of a computer program. Before you can operate on a given piece of data, you need to know whether or not it is valid. It doesn’t matter
if it is a date, a time, an age, or a Social Security number; the data you accept into your program will cause problems if it is in an invalid format.
Validating a data type is a perfect form of encapsulation, which makes it a perfect task to assign to a C++ class. Because we encapsulate both the data and the rules for the data type within a class, we can move that class from project to project, anywhere that the data type is needed. This saves time in implementing the class, as well as time and effort in validating and testing the class.
When you’re writing an application, take time to identify the data types you’re using. Write classes to validate, save, and load these data types and you will save yourself endless time debugging and extending your applications.
Implementing Data Validation with Classes
Follow these steps to create your own validation classes:
1. In the code editor of your choice, create a new file to hold the code for your header file.
In this example, I call my class ch26.cpp.
2. Type the code from Listing 26-1 into your file.
Better yet, copy the code from the source file on this book’s companion Web site.
Implementing Data Validation with Classes |
143 |
LISTING 26-1: THE VALIDATION CLASS
#include <string>
//Constants used in this validation #define SSN_LENGTH 9
#define SSN_DELIMITER ‘-’
//The validator class
class SSNValidator
{
//Internal member variables private:
//This is the actual SSN. std::string _ssn;
//This is the flag indicating validity. bool _valid;
1
2
protected: |
|
bool |
IsValid(const char *strSSN); |
public:
//Constructors and destructor SSNValidator();
SSNValidator( const char *ssn ); SSNValidator( const std::string& ssn ); SSNValidator( const SSNValidator& aCopy ); virtual ~SSNValidator();
//Accessors for this class
bool |
Valid() |
{ return _valid; }; |
std::string |
SSN() { return _ssn; }; |
|
void |
setSSN( |
const char *ssn); |
// Operators for this class
SSNValidator operator=( const char *ssn ); SSNValidator operator=( const std::string& ssn ); SSNValidator operator=( const SSNValidator& aCopy ); operator const char *();
};
3. Save your code in the code editor. |
4. Type the code from Listing 26-2 into your new |
This will be the definition for our Validator |
file. |
|
|
object. This class can then be included in other |
Better yet, copy the code from the source file on |
modules to do validation of the type we are |
this book’s companion Web site. |
defining. In this example, we are validating a U.S. |
|
Social Security Number. |
|
144 Technique 26: Doing Data Validation with Classes
LISTING 26-2: SOCIAL SECURITY NUMBER VALIDATOR
#include <ctype.h>
bool SSNValidator::IsValid(const char *strSSN)
{
int i;
//No NULL values allowed. if ( strSSN == NULL )
return false;
//Copy the result into a string, removing all delimiters. std::string sSSN;
for ( i=0; i<(int)strlen(strSSN); ++i ) if ( strSSN[i] != SSN_DELIMITER )
sSSN += strSSN[i];
//Must be 9 characters.
if ( strlen(sSSN.c_str()) != SSN_LENGTH ) return false;
//Check to see whether all characters are numeric. for ( i=0; i<(int)strlen(sSSN.c_str()); ++i )
if ( !isdigit( sSSN[i] ) ) return false;
//Must be okay.
return true;
}
// Constructors and destructor SSNValidator::SSNValidator()
{
_ssn = “”; _valid = false;
}
SSNValidator::SSNValidator( const char *ssn )
{
// Only assign if valid. _valid = IsValid( ssn ); if ( _valid )
_ssn = ssn;
}
SSNValidator::SSNValidator( const std::string& ssn )
{
// Only assign if valid.
_valid = IsValid( ssn.c_str() ); if ( _valid )
_ssn = ssn;
}
SSNValidator::SSNValidator( const SSNValidator& aCopy )
Implementing Data Validation with Classes |
145 |
{
_ssn = aCopy._ssn; _valid = aCopy._valid;
}
SSNValidator::~SSNValidator()
{
}
void SSNValidator::setSSN( const char *ssn)
{
// Only assign if valid. if ( IsValid( ssn ) )
{
_valid = true; _ssn = ssn;
}
}
// Operators for this class
SSNValidator SSNValidator::operator=( const char *ssn )
{
// Only assign if valid. if ( IsValid( ssn ) )
{
_valid = true; _ssn = ssn;
}
return *this;
}
SSNValidator SSNValidator::operator=( const std::string& ssn )
{
// Only assign if valid.
if ( IsValid( ssn.c_str() ) )
{
_valid = true; _ssn = ssn;
}
return *this;
}
SSNValidator SSNValidator::operator=( const SSNValidator& aCopy )
{
_valid = aCopy._valid; _ssn = aCopy._ssn; return *this;
}
SSNValidator::operator const char *()
{
return _ssn.c_str();
}