My test program, isbuffer.c:
/* Doc: demonstrate buffering of stdout and stderr */
#include <stdio.h>
int main( void ) {
int I;
for ( I = 0; I<5; I++ ) {
fprintf( stdout, "Record %2d to stdout\n", I );
fprintf( stderr, "Record %2d to stderr\n", I ); }
return( 0 ); }
... when compiled and executed with the C/C++ compiler on z/OS 1.13 prints:
SPPG@MVS3:136$ cd ../OS390
SPPG@MVS3:138$ gmake isbuffer && ./isbuffer
gmake: `isbuffer' is up to date.
Record 0 to stdout
Record 0 to stderr
Record 1 to stdout
Record 1 to stderr
Record 2 to stdout
Record 2 to stderr
Record 3 to stdout
Record 3 to stderr
Record 4 to stdout
Record 4 to stderr
... the writes to stdout and stderr come out interleaved, in the order
in which they were executed. However, when I compile in Enhanced
ASCII mode and link with xplink, I get:
SPPG@MVS3:145$ cd ../ASCII
SPPG@MVS3:146$ gmake isbuffer && ./setascii ./isbuffer
unset LC_CTYPE; \
c99 -I.. -D_ALL_SOURCE -Wa,"ASA,RENT" -Wl,xplink,EDIT=NO -Wc,dll,ascii -o
isbuffer isbuffer.o /usr/lib/Xaw.x /usr/lib/SM.x /usr/lib/ICE.x /usr/lib/X11.x
-lcurses
Record 0 to stderr
Record 1 to stderr
Record 2 to stderr
Record 3 to stderr
Record 4 to stderr
Record 0 to stdout
Record 1 to stdout
Record 2 to stdout
Record 3 to stdout
Record 4 to stdout
... all the writes to stderr come out first, and stdout appears to be
using a lazy buffer. Is this documented? Is there a standard
involved? Or just a good argument for issuing prompts to stderr
rather than to stdout in an interactive program? (Or for using
fflush().)
-- gil
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