[unix-history] / .ref-BSD-3 / usr / doc / libNS / fopen.3

.TH FOPEN 3 4/8/79 3
.SH NAME
fopen, freopen \- open a stream
.SH SYNOPSIS
.B #include <nstdio.h>
.PP
.SM
.B FILE
.B *fopen(filename, type)
.br
.B char *filename, *type;
.PP
.SM
.B FILE
.B *freopen(filename, type, stream)
.br
.B char *filename, *type;
.br
.SM
.B FILE
.B *stream;
.SH DESCRIPTION
.I Fopen
opens the file named by
.I filename
and associates a stream with it.
.I Fopen
returns a pointer to be used to identify
the stream in subsequent operations.
.PP
.I Type
is a character string having one of the following values:
.TP 5
"r"
open for reading
.ns
.TP 5
"w"
create for writing
.ns
.TP 5
"rw" or "w+"
Create for concurrent read/write access.
The file is first truncated, if it exists,
and created if it does not.
.ns
.TP 5
"a"
Append: open for writing at end
of file, or create for writing
.ns
.TP 5
"ra" or "a+"
Read and append: open for concurrent read/write access  at end
of file, or create file and open with such access
.ns
.TP 5
"r+"
Read and write: open for both reading and writing
but do not truncate the file first.
.PP
.I Freopen
substitutes the named file in place
of the open
.IR stream .
It returns the original value of
.IR stream .
The original stream is closed.
.PP
.I Freopen
is typically used to attach the preopened
constant names,
.B stdin, stdout, stderr,
to specified files.
.SH "SEE ALSO"
open(2),
fclose(3)
.SH DIAGNOSTICS
.I Fopen
and 
.I freopen
return the pointer
.SM
.B NULL
if
.I filename
cannot be accessed.
.SH BUGS
The "+" syntax is included merely for compatibility with the USG
stdio, and is not to be viewed as true support.
The USG stdio has restrictions on how you can switch from reading
to writing or vice versa.
LibNS has no such restrictions, at a small runtime cost.
Commit	Line	Data
0f4b110b KS	1	.TH FOPEN 3 4/8/79 3
	2	.SH NAME
	3	fopen, freopen \- open a stream
	4	.SH SYNOPSIS
	5	.B #include <nstdio.h>
	6	.PP
	7	.SM
	8	.B FILE
	9	.B *fopen(filename, type)
	10	.br
	11	.B char filename, type;
	12	.PP
	13	.SM
	14	.B FILE
	15	.B *freopen(filename, type, stream)
	16	.br
	17	.B char filename, type;
	18	.br
	19	.SM
	20	.B FILE
	21	.B *stream;
	22	.SH DESCRIPTION
	23	.I Fopen
	24	opens the file named by
	25	.I filename
	26	and associates a stream with it.
	27	.I Fopen
	28	returns a pointer to be used to identify
	29	the stream in subsequent operations.
	30	.PP
	31	.I Type
	32	is a character string having one of the following values:
	33	.TP 5
	34	"r"
	35	open for reading
	36	.ns
	37	.TP 5
	38	"w"
	39	create for writing
	40	.ns
	41	.TP 5
	42	"rw" or "w+"
	43	Create for concurrent read/write access.
	44	The file is first truncated, if it exists,
	45	and created if it does not.
	46	.ns
	47	.TP 5
	48	"a"
	49	Append: open for writing at end
	50	of file, or create for writing
	51	.ns
	52	.TP 5
	53	"ra" or "a+"
	54	Read and append: open for concurrent read/write access at end
	55	of file, or create file and open with such access
	56	.ns
	57	.TP 5
	58	"r+"
	59	Read and write: open for both reading and writing
	60	but do not truncate the file first.
	61	.PP
	62	.I Freopen
	63	substitutes the named file in place
	64	of the open
65	.IR stream .
66	It returns the original value of
67	.IR stream .
68	The original stream is closed.
69	.PP
70	.I Freopen
71	is typically used to attach the preopened
72	constant names,
73	.B stdin, stdout, stderr,
74	to specified files.
75	.SH "SEE ALSO"
76	open(2),
77	fclose(3)
78	.SH DIAGNOSTICS
79	.I Fopen
80	and
81	.I freopen
82	return the pointer
83	.SM
84	.B NULL
85	if
86	.I filename
87	cannot be accessed.
88	.SH BUGS
89	The "+" syntax is included merely for compatibility with the USG
90	stdio, and is not to be viewed as true support.
91	The USG stdio has restrictions on how you can switch from reading
92	to writing or vice versa.
93	LibNS has no such restrictions, at a small runtime cost.