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<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >C library startup</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="C and math library overview" HREF="c-and-math-library-overview.html"><LINK REL="PREVIOUS" TITLE="Thread safety" HREF="libc-thread-safety.html"><LINK REL="NEXT" TITLE="I/O Package (Device Drivers)" HREF="io.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="libc-thread-safety.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 13. C and math library overview</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="io.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="C-LIBRARY-STARTUP">C library startup</H1 ><P >The C library includes a function declared as:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >void <TT CLASS="FUNCTION" >cyg_iso_c_start</TT >( void )</PRE ></TD ></TR ></TABLE ><P >This function is used to start an environment in which an ISO C style program can run in the most compatible way.</P ><P >What this function does is to create a thread which will invoke <TT CLASS="FUNCTION" >main()</TT > — normally considered a program's entry point. In particular, it can supply arguments to <TT CLASS="FUNCTION" >main()</TT > using the CYGDAT_LIBC_ARGUMENTS configuration option, and when returning from <TT CLASS="FUNCTION" >main()</TT >, or calling <TT CLASS="FUNCTION" >exit()</TT >, pending stdio file output is flushed and any functions registered with <TT CLASS="FUNCTION" >atexit()</TT > are invoked. This is all compliant with the ISO C standard in this respect. </P ><P >This thread starts execution when the <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >eCos</I ></SPAN > scheduler is started. If the <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >eCos</I ></SPAN > kernel package is not available (and hence there is no scheduler), then <TT CLASS="FUNCTION" >cyg_iso_c_start()</TT > will invoke the <TT CLASS="FUNCTION" >main()</TT > function directly, i.e. it will not return until the <TT CLASS="FUNCTION" >main()</TT > function returns. </P ><P >The <TT CLASS="FUNCTION" >main()</TT > function should be defined as the following, and if defined in a C++ file, should have “C” linkage: </P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >extern int <TT CLASS="FUNCTION" >main</TT >( int <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >argc,</I ></SPAN > char *<SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >argv[] </I ></SPAN >)</PRE ></TD ></TR ></TABLE ><P >The thread that is started by <TT CLASS="FUNCTION" >cyg_iso_c_start()</TT > can be manipulated directly, if you wish. For example you can suspend it. The kernel C API needs a handle to do this, which is available by including the following in your source code.</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >extern cyg_handle_t cyg_libc_main_thread;</PRE ></TD ></TR ></TABLE ><P >Then for example, you can suspend the thread with the line:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >cyg_thread_suspend( cyg_libc_main_thread );</PRE ></TD ></TR ></TABLE ><P >If you call <TT CLASS="FUNCTION" >cyg_iso_c_start()</TT > and do not provide your own <TT CLASS="FUNCTION" >main()</TT > function, the system will provide a <TT CLASS="FUNCTION" >main()</TT > for you which will simply return immediately.</P ><P >In the default configuration, <TT CLASS="FUNCTION" >cyg_iso_c_start()</TT > is invoked automatically by the <TT CLASS="FUNCTION" >cyg_package_start()</TT > function in the infrastructure configuration. This means that in the simplest case, your program can indeed consist of simply:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >int main( int argc, char *argv[] ) { printf("Hello eCos\n"); }</PRE ></TD ></TR ></TABLE ><P >If you override <TT CLASS="FUNCTION" >cyg_package_start()</TT > or <TT CLASS="FUNCTION" >cyg_start()</TT >, or disable the infrastructure configuration option CYGSEM_START_ISO_C_COMPATIBILITY then you must ensure that you call <TT CLASS="FUNCTION" >cyg_iso_c_start()</TT > yourself if you want to be able to have your program start at the entry point of <TT CLASS="FUNCTION" >main()</TT > automatically.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="libc-thread-safety.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="io.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Thread safety</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c-and-math-library-overview.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >I/O Package (Device Drivers)</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
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