asn1_read_value_type man page

asn1_read_value_type — API function


#include <libtasn1.h>

int asn1_read_value_type(asn1_node root, const char * name, void * ivalue, int * len, unsigned int * etype);


asn1_node root

pointer to a structure.

const char * name

the name of the element inside a structure that you want to read.

void * ivalue

vector that will contain the element's content, must be a pointer to memory cells already allocated (may be NULL).

int * len

number of bytes of *value: value[0]..value[len-1]. Initialy holds the sizeof value.

unsigned int * etype

The type of the value read (ASN1_ETYPE)


Returns the type and value of one element inside a structure.  If an element is OPTIONAL and this returns ASN1_ELEMENT_NOT_FOUND, it means that this element wasn't present in the der encoding that created the structure.  The first element of a SEQUENCE_OF or SET_OF is named "?1". The second one "?2" and so on. If the  root provided is a node to specific sequence element, then the keyword "?CURRENT" is also acceptable and indicates the current sequence element of this node.

Note that there can be valid values with length zero. In these case this function will succeed and  len will be zero.


VALUE will contain a two's complement form integer.

integer=-1  -> value[0]=0xFF , len=1. integer=1   -> value[0]=0x01 , len=1.


As Integer (but only with not negative numbers).


VALUE will be the null terminated string "TRUE" or "FALSE" and LEN=5 or LEN=6.

OBJECT IDENTIFIER: VALUE will be a null terminated string with each number separated by a dot (i.e. "").

LEN = strlen(VALUE)+1


VALUE will be a null terminated string in one of these formats: "YYMMDDhhmmss+hh'mm'" or "YYMMDDhhmmss-hh'mm'". LEN=strlen(VALUE)+1.


VALUE will be a null terminated string in the same format used to set the value.

OCTET STRING: VALUE will contain the octet string and LEN will be the number of octets.


VALUE will contain the generalstring and LEN will be the number of octets.

BIT STRING: VALUE will contain the bit string organized by bytes and LEN will be the number of bits.


If NAME indicates a choice type, VALUE will specify the alternative selected.


If NAME indicates an any type, VALUE will indicate the DER encoding of the structure actually used.


ASN1_SUCCESS if value is returned, ASN1_ELEMENT_NOT_FOUND if  name is not a valid element, ASN1_VALUE_NOT_FOUND if there isn't any value for the element selected, and ASN1_MEM_ERROR if The value vector isn't big enough to store the result, and in this case  len will contain the number of bytes needed.

See Also

The full documentation for libtasn1 is maintained as a Texinfo manual.  If the info and libtasn1 programs are properly installed at your site, the command

info libtasn1

should give you access to the complete manual. As an alternative you may obtain the manual from:


4.8 libtasn1