---
name: "fmt_asn1dertag"
section: "3"
platform: "linux"
package: "libowfat-dev"
version: "0.32-5"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/fmt_asn1dertag"
---

# fmt\_asn1dertag(3)

encode unsigned integer like ASN.1 DER tag

## NAME

fmt\_asn1dertag - encode unsigned integer like ASN.1 DER tag

## SYNTAX

**#include \<libowfat/fmt.h\>**

size\_t **fmt\_asn1dertag**(char \**dest*,unsigned long long *source*);

## DESCRIPTION

fmt\_asn1dertag encodes an unsigned integer using the ASN.1 DER for encoding tag.  This takes one byte for every 7 bits in the number.

If *dest* equals FMT\_LEN (i.e. is NULL), fmt\_asn1dertag returns the number of bytes it would have written.

For convenience, fmt.h defines the integer FMT\_ASN1TAG to be big enough to contain every possible fmt\_asn1dertag output.

## SEE ALSO

[scan\_asn1dertag(3)](/scan_asn1dertag/3.md)