character array validation in C++ - c++

Question

I have to validate my data "123-AB-12345" as correct using character array. I set char array size to 13 including '\0'. The function must return false if the condition is not satisfied. ALL I done is that the program validates these 12 chracters but IT DOESN'T RETURN FALSE WHEN I PASS MORE VALUES like as "123-AB-123456789" and it is returning true. My program is follwing:
#include<iostream>
using namespace std;
bool isValidBookId(char bookId[13]);
int main()
{
char book[13];
cin.getline(book,13);
bool id = isValidBookId(book);
cout<<id;
}
bool isValidBookId( char bookId[13] ) {
/* Valid: 098-EN-98712 */
if ( bookId[12] != '\0' )
return false;
if ( bookId[3] != '-' )
return false;
if ( bookId[6] != '-' )
return false;
for ( int i = 0; i < 3; i++ ) {
if ( bookId[i] < '0' || bookId[i] > '9' ) {
return false;
}
}
for ( int i = 4; i < 6; i++ ) {
if ( bookId[i] < 'A' || bookId[i] > 'Z' ) {
return false;
}
}
for ( int i = 7; i < 12 || bookId[12]!='\0'; i++ ) {
if(bookId[13]!='\0'){
return false;
}
if ( bookId[i] < '0' || bookId[i] > '9' ) {
return false;
}
}
return true;
}
I don't know why this condition is not working.
if ( bookId[12] != '\0' )
return false;

Answer 1

Looking at your code, the only explanation is that the last character of your array is null. Try specifying a delimiter character like this:
cin.getline(book, 13, '\n');
I'd refer to this link:
"A null character ('\0') is automatically appended to the written sequence if n is greater than zero, even if an empty string is extracted."

Answer 2

Your issue is in your input function:
You only read up to 12 characters. So you cannot have more than 12 characters.
You might use std::string
bool isValidBookId(const std::string&s) {
static const std::regex r{R"(^\d{3}-[A-Z]{2}-\d{5}$)"};
return std::regex_match(std::begin(s), std::end(s), r);
}
int main()
{
std::string s;
while (std::getline(std::cin, s))
{
std::cout << s << ": " << isValidBookId(s) << std::endl;
}
}
Demo
Or bigger buffer:
bool isValidBookId(const char (&s)[14]) {
static const std::regex r{R"(^\d{3}-[A-Z]{2}-\d{5}\0$)"};
return std::regex_match(std::begin(s), std::end(s) - 1, r);
}
int main()
{
char s[14];
while (true)
{
bool b = !!std::cin.getline(s, 14);
if (s[0] == '\0') break;
std::cout << " " << s << ": " << isValidBookId(s) << std::endl;
if (!b) {
std::cin.clear();
std::cin.ignore(255, '\n');
}
}
}
Demo

Answer 3

All conditions are correct. Your problem is created initially when entering data.
cin.getline(book,13);
The 'getline' method accepts any number of characters (of course within reason), but allocates space only for the first 12 characters and the 13th will always be only '\ 0'. If you want to write more characters, let me enter more characters.
The correct option is:
bool isValidBookId(char bookId[100]); // now there is a restriction of not 13 characters, but 100
int main()
{
char book[100]; // now there is a restriction of not 13 characters, but 100
cin.getline(book,100); // now there is a restriction of not 13 characters, but 100
}
bool isValidBookId( char bookId[100] ) // now there is a restriction of not 13 characters, but 100
{...}

Answer 4

As pointed above,
cin.getline(book,13) wont save more than 12 characters in your array.
Instead replace your code with :
char book[100]; // To save upto 99 characters
cin.getline(book,100);
And change
isValidBookId(char bookId[13])
to
isValidBookId( char bookId[100] )
and remove all the checks of
bookId[12]!='\0' inside this isValidBookId function, as there can be any character at 12th index.