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<cref>
  <header>
    <copyright>
      <year>1996</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.
    
      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.
    
    </legalnotice>

    <title>erl_error</title>
    <prepared>Torbj&ouml;rn T&ouml;rnkvist</prepared>
    <responsible>Torbj&ouml;rn T&ouml;rnkvist</responsible>
    <docno></docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked>Torbj&ouml;rn T&ouml;rnkvist</checked>
    <date>961014</date>
    <rev>A</rev>
    <file>erl_error.sgml</file>
  </header>
  <lib>erl_error</lib>
  <libsummary>Error Print Routines</libsummary>
  <description>
    <p>This module contains some error printing routines taken
      from <em>Advanced Programming in the UNIX Environment</em> 
      by W. Richard Stevens. </p>
    <p>These functions are all called in the same manner as
      <c><![CDATA[printf()]]></c>, i.e. with a string containing format specifiers
      followed by a list of corresponding arguments. All output from
      these functions is to <c><![CDATA[stderr]]></c>.</p>
  </description>
  <funcs>
    <func>
      <name><ret>void</ret><nametext>erl_err_msg(FormatStr, ... )</nametext></name>
      <fsummary>Non-fatal error, and not system call error</fsummary>
      <type>
        <v>const char *FormatStr;</v>
      </type>
      <desc>
        <p>The message provided by the caller is printed. This
          function is simply a wrapper for <c><![CDATA[fprintf()]]></c>.</p>
      </desc>
    </func>
    <func>
      <name><ret>void</ret><nametext>erl_err_quit(FormatStr, ... )</nametext></name>
      <fsummary>Fatal error, but not system call error</fsummary>
      <type>
        <v>const char *FormatStr;</v>
      </type>
      <desc>
        <p>Use this function when a fatal error has occurred that
          is not due to a system call. The message provided by the
          caller is printed and the process terminates with an exit
          value of 1. The function does not return.</p>
      </desc>
    </func>
    <func>
      <name><ret>void</ret><nametext>erl_err_ret(FormatStr, ... )</nametext></name>
      <fsummary>Non-fatal system call error</fsummary>
      <type>
        <v>const char *FormatStr;</v>
      </type>
      <desc>
        <p>Use this function after a failed system call. The message
          provided by the caller is printed followed by a string
          describing the reason for failure. </p>
      </desc>
    </func>
    <func>
      <name><ret>void</ret><nametext>erl_err_sys(FormatStr, ... )</nametext></name>
      <fsummary>Fatal system call error</fsummary>
      <type>
        <v>const char *FormatStr;</v>
      </type>
      <desc>
        <p>Use this function after a failed system call. The message
          provided by the caller is printed followed by a string
          describing the reason for failure, and the process
          terminates with an exit value of 1. The function does not
          return.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Error Reporting</title>
    <p>Most functions in erl_interface report failures to the caller by
      returning some otherwise meaningless value (typically <c><![CDATA[NULL]]></c>
      or a negative number). As this only tells you that things did not
      go well, you will have to examine the error code in
      <c><![CDATA[erl_errno]]></c> if you want to find out more about the failure.</p>
  </section>
  <funcs>
    <func>
      <name><ret>volatile int</ret><nametext>erl_errno</nametext></name>
      <fsummary>The variable <c><![CDATA[erl_errno]]></c>contains the erl_interface error number. You can change the value if you wish. </fsummary>
      <desc>
        <p><c><![CDATA[erl_errno]]></c> is initially (at program startup) zero and
          is then set by many erl_interface functions on failure to a
          non-zero error code to indicate what kind of error it
          encountered. A successful function call might change
          <c><![CDATA[erl_errno]]></c> (by calling some other function that
          fails), but no function will ever set it to zero. This means
          that you cannot use <c><![CDATA[erl_errno]]></c> to see <em>if</em> a
          function call failed. Instead, each function reports failure
          in its own way (usually by returning a negative number or
          <c><![CDATA[NULL]]></c>), in which case you can examine <c><![CDATA[erl_errno]]></c>
          for details.</p>
        <p><c><![CDATA[erl_errno]]></c> uses the error codes defined in your
          system's <c><![CDATA[<errno.h>]]></c>.</p>
        <note>
          <p>Actually, <c><![CDATA[erl_errno]]></c> is a "modifiable lvalue" (just
            like ISO C defines <c><![CDATA[errno]]></c> to be) rather than a
            variable. This means it might be implemented as a macro
            (expanding to, e.g., <c><![CDATA[*_erl_errno()]]></c>). For reasons of
            thread- (or task-)safety, this is exactly what we do on most
            platforms.</p>
        </note>
      </desc>
    </func>
  </funcs>
</cref>

