Strings

The strings of the ASN1 specification are support in the Boost.ASN1 library through a templated class called string_t. This template is specialized for ten of the ASN1 string data types. The exception to this rule is the BIT STRING data type, which is covered else where.

ASN1 Type	C++ Equiv
NUMERIC STRING	numericstring_t
PRINTABLE STRING	printablestring_t
T61 STRING	t61string_t
VIDEOTEXT STRING	videotextstring_t
IA5 STRING	ia5string_t
GRAPHIC STRING	graphicstring_t
ISO646 STRING	iso646string_t
GENERAL STRING	generalstring_t
UTF8 STRING	utf8string_t
OCTET STRING	octetstring_t

The internal storage for the string_t class is a basic_string<> object of type char or wchar_t. This template class differs from the integral_t template class in that it allows only assignment, appending and retrieval of the internal data. No other basic_string<> functionality is exposed.

With the exception of strings of type OCTET, these string types have restricted character sets. For instance, the NUMERIC string only allows digit characters and spaces. Punctuation (ie, periods, dashes) is not allowed in a NUMERIC string.

numericstring_t legalNumeric("12 34");
numericstring_t illegalNumeric("12.34");

Assigning illegal characters to a restricted string type will cause the string to be blank and invalid.

As with the integral_t, assigning between string types is allowed if the strings are from within the same classification and meet the restricted requirements.

ia5string_t ia5string;
numericstring_t legalNumeric = "1234";

ia5string = legalNumeric; // Allowable assignment

ia5string("regular string");
numericstring_t illegalNumeric(ia5string); // Not allowable assignment