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NAME="C-LIBRARY-STARTUP">C library startup</H1
><P
>The C library includes a function declared as:</P
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><PRE
CLASS="PROGRAMLISTING"
>void <TT
CLASS="FUNCTION"
>cyg_iso_c_start</TT
>( void )</PRE
></TD
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><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
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> scheduler
is started. If the <SPAN
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> 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
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>extern int <TT
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>main</TT
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>
char *<SPAN
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>)</PRE
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><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
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><PRE
CLASS="PROGRAMLISTING"
>extern cyg_handle_t cyg_libc_main_thread;</PRE
></TD
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><P
>Then for example, you can suspend the thread with the line:</P
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><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
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CLASS="PROGRAMLISTING"
>int main( int argc, char *argv[] )
{
printf("Hello eCos\n");
}</PRE
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><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
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