Erlang -- Problem Example

Interoperability Tutorial

User's Guide

Version 10.6

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### Chapters

- Introduction
  - Top of chapter
  - Purpose
  - Prerequisites
- Overview
  - Top of chapter
  - Built-In Mechanisms
  - C and Java Libraries
  - Standard Protocols
  - IC and CORBA
  - Old Applications
- Problem Example
  - Top of chapter
  - Description
- Ports
  - Top of chapter
  - Erlang Program
  - C Program
  - Running the Example
- Erl_Interface
  - Top of chapter
  - Erlang Program
  - C Program
  - Running the Example
- Port Drivers
  - Top of chapter
  - Erlang Program
  - C Driver
  - Running the Example
- C Nodes
  - Top of chapter
  - Erlang Program
  - C Program
  - Running the Example
- NIFs
  - Top of chapter
  - Erlang Program
  - NIF Library Code
  - Running the Example

# 3 Problem Example

### 3.1 Description

A common interoperability situation is when you want to incorporate a piece of code, solving a complex problem, in your Erlang program. Suppose for example, that you have the following C functions that you would like to call from Erlang:

    /* complex.c */

    int foo(int x) {
      return x+1;
    }

    int bar(int y) {
      return y*2;
    }

The functions are deliberately kept as simple as possible, for readability reasons.

From an Erlang perspective, it is preferable to be able to call foo and bar without having to bother about that they are C functions:

    % Erlang code
    ...
    Res = complex:foo(X),
    ...

Here, the communication with C is hidden in the implementation of complex.erl. In the following sections, it is shown how this module can be implemented using the different interoperability mechanisms.