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.Dd September 12, 2011
.Dt OPEN_MEMSTREAM 3
.Os
.Sh NAME
.Nm open_memstream
.Nd open a stream that points to a dynamic buffer
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft FILE *
.Fn open_memstream "char **bufp" "size_t *sizep"
.Sh DESCRIPTION
The
.Fn open_memstream
function creates a
.Vt FILE
stream with a dynamically expanding buffer.
A pointer to the buffer is stored at the
.Fa bufp
argument and the length of the data in the buffer is stored at the
.Fa sizep
argument.
The pointer and length values may be updated by writes to the buffer.
.Pp
Writes append to the buffer and may reallocate it, invalidating the
.Fa bufp
argument.
Writes may fail if the buffer cannot be resized.
.Pp
The stream is seekable and opened for writing.
.Sh RETURN VALUES
Upon successful completion,
.Fn open_memstream
returns a
.Vt FILE
pointer.
Otherwise,
.Dv NULL
is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa bufp
argument or the
.Fa sizep
argument were
.Dv NULL .
.It Bq Er ENOMEM
Memory for the stream buffer or cookie could not be allocated.
.El
.Sh SEE ALSO
.Xr fclose 3 ,
.Xr fflush 3 ,
.Xr fmemopen 3 ,
.Xr fopen 3
.Sh HISTORY
The
.Fn open_memstream
function first appeared in
.Dx 2.11 .