Use scanf fuction it works better..
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
On Behalf Of fred smith
Sent: Saturday, April 06, 2002 9:58 AM
To: [EMAIL PROTECTED]
Subject: [LONG] Re: a little help for newbie in C
On Sat, Apr 06, 2002 at 11:38:28AM -0500, ramzez wrote:
> Hi
> I'm newbie in C and I want to write a string and later read a
char... but i
> don't want to see this char (I mean don't echo only for this)...
> <.../...>
> printf("Hi, i am a string\n")
> key=getchar(); //but I don't want to see the character pressed
This isn't a C question so much as it is a Unix/Linux question. Why?
Because there's no portable way to do do this cross-platform, the C
language does not provide the mechanisms you need.
However, as long as you're on Linux (or any other reasonably modern Unix
platform) you CAN do it. I've added below some excerpts from a rather
old
copy of the unix.programming.FAQ, one or more of which discusses the
sort
of thing I think you're driving at:
3. Terminal I/O
***************
3.1 How can I make my program not echo input?
=============================================
How can I make my program not echo input, like login does when
asking
for your password?
There is an easy way, and a slightly harder way:
The easy way, is to use `getpass()', which is probably found on almost
all
Unices. It takes a string to use as a prompt. It will read up to an
`EOF'
or newline and returns a pointer to a static area of memory holding the
string typed in.
The harder way is to use `tcgetattr()' and `tcsetattr()', both use a
`struct termios' to manipulate the terminal. The following two routines
should allow echoing, and non-echoing mode.
#include <stdlib.h>
#include <stdio.h>
#include <termios.h>
#include <string.h>
static struct termios stored;
void echo_off(void)
{
struct termios new;
tcgetattr(0,&stored);
memcpy(&new, &stored, sizeof(struct termios));
new.c_lflag &= (~ECHO);
tcsetattr(0,TCSANOW,&new);
return;
}
void echo_on(void)
{
tcsetattr(0,TCSANOW,&stored);
return;
}
Both routines used, are defined by the POSIX standard.
3.2 How can I read single characters from the terminal?
=======================================================
How can I read single characters from the terminal? My program is
always waiting for the user to press `<RETURN>'.
Terminals are usually in canonical mode, where input is read in lines
after
it is edited. You may set this into non-canonical mode, where you set
how
many characters should be read before input is given to your program.
You
also may set the timer in non-canonical mode terminals to 0, this timer
flushs your buffer at set intervals. By doing this, you can use `getc()'
to
grab the key pressed immediately by the user. We use `tcgetattr()' and
`tcsetattr()' both of which are defined by POSIX to manipulate the
`termios' structure.
#include <stdlib.h>
#include <stdio.h>
#include <termios.h>
#include <string.h>
static struct termios stored;
void set_keypress(void)
{
struct termios new;
tcgetattr(0,&stored);
memcpy(&new,&stored,sizeof(struct termios));
/* Disable canonical mode, and set buffer size to 1 byte */
new.c_lflag &= (~ICANON);
new.c_cc[VTIME] = 0;
new.c_cc[VMIN] = 1;
tcsetattr(0,TCSANOW,&new);
return;
}
void reset_keypress(void)
{
tcsetattr(0,TCSANOW,&stored);
return;
}
3.3 How can I check and see if a key was pressed?
=================================================
How can I check and see if a key was pressed? On DOS I use the
`kbhit()' function, but there doesn't seem to be an equivalent?
If you set the terminal to single-character mode (see previous answer),
then (on most systems) you can use `select()' or `poll()' to test for
readability.
<snip>
3.6.2 Setting up termios flags
------------------------------
Some hints on setting up the termios flags when using a serial device
that
you've opened yourself (as opposed to using your existing control tty):
3.6.2.1 c_iflag
...............
You probably want to set *all* the bits in `c_iflag' to 0, unless you
want
to use software flow control (ick) in which case you set `IXON' and
`IXOFF'.
3.6.2.2 c_oflag
...............
Most of the bits of `c_oflag' are hacks of one sort or another to make
output to slow terminals work, and as such some newer systems have
dropped
almost all of them as obsolete (especially all the gory output-padding
options). As with `c_iflag', setting everything to 0 is reasonable for
most
applications.
3.6.2.3 c_cflag
...............
When setting the character size, remember to mask using `CSIZE' first;
e.g.
to set 8-bit characters, use:
attr.c_cflag &= ~CSIZE;
attr.c_cflag |= CS8;
Other important flags found in `c_cflag' that you probably want to turn
*on* and `CREAD' and `HUPCL'.
If you need to generate even parity, then set `PARENB' and clear
`PARODD';
if you need to generate odd parity then set both `PARENB' and `PARODD'.
If
you don't want parity at all, then make sure `PARENB' is clear.
Clear `CSTOPB' unless you actually need to generate two stop bits.
Flags for enabling hardware flow control may also be found in `c_cflag',
but they aren't standardised (pity).
3.6.2.4 c_lflag
...............
Most applications will probably want to turn off `ICANON' (canonical,
i.e.
line-based, input processing), `ECHO', and `ISIG'.
`IEXTEN' is a more complex issue. If you don't turn it off, the
implementation is allowed to do nonstandard things (like define
additional
control characters in `c_cc') that might cause unexpected results, but
you
might need to leave `IEXTEN' enabled on some systems to get useful
features
like hardware flow control.
3.6.2.5 c_cc
............
This is an array of characters that have special meanings on input.
These
characters are given names like `VINTR', `VSTOP' etc.; the names are
indexes into the array.
(Two of these "characters" are not really characters at all, but control
the behaviour of `read()' when `ICANON' is disabled; these are `VMIN'
and
`VTIME'.)
The indexes are often referred to as though they were actual variables,
e.g. "set VMIN to 1" actually means "set c_cc[VMIN] to 1". The shorthand
is
useful and only occasionally confusing.
Many of the slots in `c_cc' are only used if some other combination of
flags is set:
Used only if `ICANON' is set
`VEOF', `VEOL', `VERASE', `VKILL' (and also `VEOL2', `VSTATUS' and
`VWERASE' if defined and `IEXTEN' is set)
Used only if `ISIG' is set
`VINTR', `VQUIT', `VSUSP' (and also `VDSUSP' if defined and
`IEXTEN'
is set)
Used only if `IXON' or `IXOFF' is set
`VSTOP', `VSTART'
Used only if `ICANON' is *not* set
`VMIN', `VTIME'
Implementations may define additional entries in `c_cc'. It may be
prudent
to initialise all the entries to `_POSIX_VDISABLE' (the constant `NCCS'
gives the array size) before setting the specific values you wish to
use.
`VMIN' and `VTIME' (which may share slots with `VEOF' and `VEOL'
respectively, depending on the implementation) have the following
meaning.
The value of `VTIME' is (if not 0) always interpreted as a timer in
tenths
of seconds.
`c_cc[VMIN] > 0, c_cc[VTIME] > 0'
`read()' will return when either VMIN bytes of input are available,
or
if at least one character has been read and VTIME has expired
between
characters, or if interrupted by a signal.
`c_cc[VMIN] > 0, c_cc[VTIME] == 0'
`read()' will return when VMIN bytes of input are available, or if
interrupted. Otherwise it will wait indefinitely.
`c_cc[VMIN] == 0, c_cc[VTIME] > 0'
`read()' will return as soon as any input is available; if VTIME
expires with no data arriving, it will return with no characters
read.
(This conflicts slightly with the end-of-file indication received
in
the event of modem hangup; using 1 for VMIN and either `alarm()' or
`select()' for a timeout avoids this particular problem.)
`c_cc[VMIN] == 0, c_cc[VTIME] == 0'
`read()' will always return immediately; if no data is available it
will return with no characters read (with the same problem as
above).
--
---- Fred Smith -- [EMAIL PROTECTED]
-----------------------------
"And he will be called Wonderful Counselor, Mighty God, Everlasting
Father,
Prince of Peace. Of the increase of his government there will be no
end. He
will reign on David's throne and over his kingdom, establishing and
upholding
it with justice and righteousness from that time on and forever."
------------------------------- Isaiah 9:7 (niv)
------------------------------
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