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The ASN.1 Compiler
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If you haven't installed the asn1c yet, read the INSTALL file for a short installation guide.


For the list of asn1c command line options, see asn1c -h or man asn1c.

The comprehensive documentation on this compiler is in asn1c-usage.pdf.

If you are building the compiler from the sources, the PDFs reside in the ./doc directory. Normally the file is installed together with the file you're reading right now.

Please also read the FAQ file.

An excellent book on ASN.1 is written by Olivier Dubuisson: "ASN.1 Communication between heterogeneous systems", ISBN:0-12-6333361-0.

Quick start

(also check out asn1c-quick.pdf)

After building [and installing] the compiler (see INSTALL), you may use the asn1c command to compile the ASN.1 specification:

asn1c <module.asn1>                         # Compile module

If several specifications contain interdependencies, all of them must be specified:

asn1c <module1.asn1> <module2.asn1> ...     # Compile interdependent modules

If you are building the asn1c from the sources, the ./examples directory contains several ASN.1 modules and a script to extract the ASN.1 modules from RFC documents. Refer to the README file in that directory. To compile the X.509 PKI module:

./asn1c/asn1c -P ./examples/rfc3280-*.asn1  # Compile-n-print

In this example, -P option is used to instruct the compiler to print the compiled text on the standard output instead of creating multiple .c and .h files for every ASN.1 type found inside the specified ASN.1 modules. This is useful for debugging and test automation.

The compiler -E and -EF options are used for testing the parser and the semantic fixer, respectively. These options will instruct the compiler to dump out the parsed (and fixed) ASN.1 specification as it was "understood" by the compiler. It might be useful for checking whether a particular syntactic construction is properly supported by the compiler.

asn1c -EF <module-to-test.asn1>     # Check semantic validity

Model of operation

The asn1c compiler works by processing the ASN.1 module specifications in several stages:

  1. In the first stage, the ASN.1 file is parsed. (Parsing produces an ASN.1 syntax tree for the subsequent levels)
  2. In the second stage, the syntax tree is "fixed". (Fixing is a process of checking the tree for semantic errors, accompanied by the tree transformation into the canonical form)
  3. In the third stage, the syntax tree is compiled into the target language.

There are several command-line options reserved for printing the results after each stage of operation:

<parser> => print                                       (-E)
<parser> => <fixer> => print                            (-E -F)
<parser> => <fixer> => <compiler> => print              (-P)
<parser> => <fixer> => <compiler> => save-compiled      [default]

Lev Walkin

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