fmemopen.3: Greatly expand description of 'mode' argument

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

1 files changed, 30 insertions, 12 deletions

diff --git a/man3/fmemopen.3 b/man3/fmemopen.3
index 5fb7fda2cf..444b19356c 100644
--- a/man3/fmemopen.3
+++ b/man3/fmemopen.3
@@ -51,19 +51,37 @@ function opens a stream that permits the access specified by
 The stream allows I/O to be performed on the string or memory buffer
 pointed to by
 .IR buf .
-This buffer must be at least
-.I size
-bytes long.
-.PP
-The argument
-.I mode
-is the same as for
-.BR fopen (3).
-If
+
+The
 .I mode
-specifies an append mode, then the initial file position is set to
-the location of the first null byte (\(aq\\0\(aq) in the buffer;
-otherwise the initial file position is set to the start of the buffer.
+argument specifies the semantics of I/O on the stream,
+and is one of the following:
+.TP 8
+.I r
+The stream is opened for reading.
+.TP
+.I w
+The stream is opened for writing.
+.TP
+.I a
+Append; open the stream for writing,
+with the file initial position set to the first null byte.
+.TP
+.I r+
+Open the stream for reading and writing.
+.TP
+.I w+
+Open the stream for reading and writing.
+The buffer contents are truncated
+(i.e., \(aq\\0\(aq is placed in the first byte of the buffer).
+.TP
+.I a+
+Append; open the stream for reading and writing,
+with the file initial position set to the first null byte.
+.PP
+In all modes other than append,
+the initial position is set to the start of the buffer.
+.PP
 Since glibc 2.9,
 the letter \(aqb\(aq may be specified as the second character in
 .IR mode .