fex_set_log man page on Solaris

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fex_set_log(3M)		Mathematical Library Functions	       fex_set_log(3M)

NAME
       fex_set_log,    fex_get_log,    fex_set_log_depth,   fex_get_log_depth,
       fex_log_entry - log retrospective diagnostics for floating point excep‐
       tions

SYNOPSIS
       c99 [ flag... ] file... -lm [ library... ]
       #include <fenv.h>

       int fex_set_log(FILE *fp);

       FILE *fex_get_log(void);

       int fex_set_log_depth(int depth);

       int fex_get_log_depth(void);

       void fex_log_entry(const char *msg);

DESCRIPTION
       The  fex_set_log() function enables logging of retrospective diagnostic
       messages regarding floating point exceptions to the file	 specified  by
       fp.   If	 fp is NULL, logging is disabled.  When a program starts, log‐
       ging is initially disabled.

       The occurrence of any of the twelve exceptions listed  in  fex_set_han‐
       dling(3M)  constitutes an event that can be logged.  To prevent the log
       from becoming exhorbitantly  long,  the	logging	 mechanism  eliminates
       redundant  entries by two methods.  First, each exception is associated
       with a site in the program.  The site is identified by the  address  of
       the  instruction that caused the exception together with a stack trace.
       Only the first exception of a given type to occur at a given site  will
       be  logged.   Second,  when  FEX_NONSTOP handling mode is in effect for
       some exception, only those occurrences of that exception that  set  its
       previously  clear  flag	are  logged.  Clearing a flag using feclearex‐
       cept() allows the next occurrence of the exception to  be  logged  pro‐
       vided it does not occur at a site at which it was previously logged.

       Each  of	 the  different	 types	of invalid operation exceptions can be
       logged at the same site.	  Because  all	invalid	 operation  exceptions
       share the same flag, however, of those types for which FEX_NONSTOP mode
       is in effect, only the first exception to set the flag will be logged.
	When the invalid operation exception is raised by a call to feraiseex‐
       cept(3M)	 or feupdateenv(3M), which type of invalid operation is logged
       depends on the implementation.

       If an exception results in the creation of a log entry,	the  entry  is
       created	at the time the exception occurs and before any exception han‐
       dling actions selected with fex_set_handling() are taken.  In  particu‐
       lar,  the  log  entry  is available even if the program terminates as a
       result of the exception.	 The log entry shows the  type	of  exception,
       the  address of the instruction that caused it, how it will be handled,
       and the stack trace. If symbols	are  available,	 the  address  of  the
       excepting instruction and the addresses in the stack trace are followed
       by the names of the corresponding symbols.

       The fex_get_log() function returns the current log file.

       The fex_set_log_depth() sets the	 maximum  depth	 of  the  stack	 trace
       recorded	 with each exception to depth stack frames.  The default depth
       is 100.

       Thefex_get_log_depth() function returns the current maximum stack trace
       depth.

       The  fex_log_entry()  function  adds  a user-supplied entry to the log.
       The entry includes the string pointed to by msg and  the	 stack	trace.
       Like  entries  for  floating  point exceptions, redundant user-supplied
       entries are eliminated: only the first user-supplied entry with a given
       msg  to be requested from a given site will be logged.  For the purpose
       of a user-supplied entry, the site is defined only by the stack	trace,
       which begins with the function that called fex_log_entry().

RETURN VALUES
       The  fex_set_log()  function  returns  a	 non-zero  value if logging is
       enabled	or  disabled  accordingly  and	returns	 0   otherwise.	   The
       fex_set_log_depth()  returns  a	non-zero  value if the requested stack
       trace depth is established (regardless of whether logging  is  enabled)
       and returns 0 otherwise.

EXAMPLES
       The following example demonstrates the output generated when a floating
       point overflow occurs in sscanf(3C).

       #include <fenv.h>

       int
       main() {
	    double x;
       /*
	* enable logging of retrospective diagnostics
	*/
	    (void) fex_set_log(stdout);
       /*
	* establish default handling for overflows
	*/
	    (void) fex_set_handling(FEX_OVERFLOW, FEX_NONSTOP, NULL);
       /*
	* trigger an overflow in sscanf
	*/
	    (void) sscanf("1.0e+400", "%lf", &x);
	    return 0;
       }

       The output from the preceding program reads:

       Floating point overflow at 0xef71cac4 __base_conversion_set_exception, nonstop mode
	  0xef71cacc  __base_conversion_set_exception
	  0xef721820  _decimal_to_double
	  0xef75aba8  number
	  0xef75a94c  __doscan_u
	  0xef75ecf8  sscanf
	  0x00010f20  main

       Recompiling the program or running it on	 another  system  can  produce
       different text addresses from those shown above.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌─────────────────────────────┬─────────────────────────────┐
       │      ATTRIBUTE TYPE	     │	    ATTRIBUTE VALUE	   │
       │Availability		     │SUNWlibms, SUNWlmxs	   │
       │Interface Stability	     │Stable			   │
       │MT-Level		     │MT-Safe (see NOTES)	   │
       └─────────────────────────────┴─────────────────────────────┘

SEE ALSO
       feclearexcept(3M),  fegetenv(3M),  feraiseexcept(3M),  feupdateenv(3M),
       fex_set_handling(3M), attributes(5)

       Numerical Computation Guide

NOTES
       All threads in a process	 share	the  same  log	file.	Each  call  to
       fex_set_log() preempts the previous one.

       In addition to the log file itself, two additional file descriptors are
       used during the creation of a log entry in order to obtain symbol names
       from  the  executable  and  any	shared	objects	 it  uses.  These file
       descriptors are relinquished once the log entry	is  written.   If  the
       file  descriptors  cannot  be allocated, symbols names are omitted from
       the stack trace.

       The functions described on this page automatically  install  and	 dein‐
       stall  SIGFPE  handlers	and set and clear the trap enable mode bits in
       the floating point status register as needed.  If a program uses	 these
       functions  and attempts to install a SIGFPE handler or control the trap
       enable mode bits independently, the resulting behavior is not defined.

       As described in fex_set_handling(), when a handling function  installed
       in  FEX_CUSTOM  mode  is invoked, all exception traps are disabled (and
       will not be reenabled while SIGFPE is  blocked).	  Thus,	 retrospective
       diagnostic  messages  are  not  logged for exceptions that occur within
       such a handler.

SunOS 5.10			  12 Jul 2006		       fex_set_log(3M)
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