document internal memory allocation, how to avoid

SCCS-vsn: lib/libc/stdio/fopen.3 6.2

diff --git a/usr/src/lib/libc/stdio/fopen.3 b/usr/src/lib/libc/stdio/fopen.3
index 3f0feec..f554b54 100644 (file)
--- a/usr/src/lib/libc/stdio/fopen.3
+++ b/usr/src/lib/libc/stdio/fopen.3
@@ -2,7 +2,7 @@
 .\" All rights reserved.  The Berkeley software License Agreement
 .\" specifies the terms and conditions for redistribution.
 .\"
 .\" All rights reserved.  The Berkeley software License Agreement
 .\" specifies the terms and conditions for redistribution.
 .\"

-.\"    @(#)fopen.3     6.1 (Berkeley) %G%
+.\"    @(#)fopen.3     6.2 (Berkeley) %G%

 .\"
 .TH FOPEN 3S  ""
 .UC 4
 .\"
 .TH FOPEN 3S  ""
 .UC 4


@@ -95,7 +95,9 @@ return the pointer
 .B NULL
 if
 .I filename
 .B NULL
 if
 .I filename

-cannot be accessed.
+cannot be accessed,
+if too many files are already open,
+or if other resources needed cannot be allocated.

 .SH BUGS
 .I Fdopen
 is not portable to systems other than UNIX.
 .SH BUGS
 .I Fdopen
 is not portable to systems other than UNIX.


@@ -106,3 +108,14 @@ do not exist on all systems.  Those systems without
 read/write modes will probably treat the 
 .I type
 as if the '+' was not present.  These are unreliable in any event.
 read/write modes will probably treat the 
 .I type
 as if the '+' was not present.  These are unreliable in any event.

+.PP
+In order to support the same number of open files as does the system,
+.I fopen
+must allocate additional memory for data structures using
+.I calloc
+after 20 files have been opened.
+This confuses some programs which use their own memory allocators.
+An undocumented routine,
+.IR f_prealloc ,
+may be called to force immediate allocation of all internal memory
+except for buffers.