how to print ASCII "ETX" character?

[jeffpierce12]

Hello,

I am trying to send some characters to a scanner that I have hooked up
to the COM 1 port on my PC. I am running Linux operating system, and I
have the following sample program:

#include <stdio.h>

int main (void)
{
FILE *fd;

fd = fopen("/dev/ttyS0", "w");
fprintf (fd, "2");
fprintf (fd, "B");
<here>
fprintf (fd, "0");
fprintf (fd, "A");

fclose(fd);
return 0;
}

At the <here> line, I would like to send to the device an ASCII "ETX"
character, which is a hex 03. What is the syntax of the fprintf
statement to do this?

Thank you.

 

[Michael]

#include <stdio.h>

int main (void)
{
FILE *fd;

fd = fopen("/dev/ttyS0", "w");
fprintf (fd, "2");
fprintf (fd, "B");
<here>
fprintf (fd, "0");
fprintf (fd, "A");

fclose(fd);
return 0;
}

At the <here> line, I would like to send to the device an ASCII "ETX"
character, which is a hex 03. What is the syntax of the fprintf
statement to do this?

fprintf(fd, "%c", 0x03);

Note: You should also change your other fprintfs to look like:
fprintf(fd, "%c", '2');
etc.

fprintf is expecting a file descriptor, a format argument, and
argument(s) to that. The code you have will work, but is dangerous. I
once had to track down a seg fault where someone had done this:
void foo(char* str) {
fprintf(fd, str);
}
instead of
void foo(char* str) {
fprintf(fd, "%s", str);
}


That worked fine until str contained a percent sign, then it seg
faulted.

Be nice to future programmers; use the correct form.

Michael

 

[Walter Roberson]

At the <here> line, I would like to send to the device an ASCII "ETX"
character, which is a hex 03. What is the syntax of the fprintf
statement to do this?

Choices:

putc(0x03, fd);

fprintf(fd, "\3");

fprintf(fd, "%c", 3);


It is recommended not to use fprintf() if you are not doing any
formatting -- putc() and fputs() and fwrite() are usually more
efficient.

 

[Mike Wahler]

Hello,

I am trying to send some characters to a scanner that I have hooked up
to the COM 1 port on my PC. I am running Linux operating system, and I
have the following sample program:

#include <stdio.h>

int main (void)
{
FILE *fd;

fd = fopen("/dev/ttyS0", "w");
fprintf (fd, "2");

This will write two characters to 'fd':
'2' and '\0'. Is that what you wanted?

fprintf (fd, "B");

This will write two characters to 'fd':
'B' and '\0'. Is that what you wanted?

<here>
fprintf (fd, "0");

This will write two characters to 'fd':
'0' and '\0'. Is that what you wanted?

fprintf (fd, "A");

This will write two characters to 'fd':
'A' and '\0'. Is that what you wanted?

fclose(fd);
return 0;
}

At the <here> line, I would like to send to the device an ASCII "ETX"
character, which is a hex 03. What is the syntax of the fprintf
statement to do this?

if(fprintf(fd, "%c", (char)3) != 1)
; /* something wrong */


Note that the format specifier for a single character
is %c, not %s.

Also, in all cases, you should be checking the return
value from 'fprintf()'. It can fail, but you won't
know unless you check.


-Mike

 

[Walter Roberson]

fprintf (fd, "2");

[/QUOTE]

This will write two characters to 'fd':
'2' and '\0'. Is that what you wanted?

No it won't. The \0 of the string literal "2" terminates the
format -- otherwise -every- printf and fprintf would put in the
extra \0.

 

[SM Ryan]

(e-mail address removed) wrote:
# Hello,
#
# I am trying to send some characters to a scanner that I have hooked up
# to the COM 1 port on my PC. I am running Linux operating system, and I
# have the following sample program:
#
# #include <stdio.h>
#
# int main (void)
# {
# FILE *fd;
#
# fd = fopen("/dev/ttyS0", "w");
# fprintf (fd, "2");
# fprintf (fd, "B");
# <here>
# fprintf (fd, "0");
# fprintf (fd, "A");

You can embed characters except '\0' in a string and print
them out alongside printable character.

So you could do
fputs("2B\x03" "0A",fd);

#define ETX "\x03"
fputs("2B" ETX "0A",fd);

fputc('2',fd); fputc('B',fd); fputc(3,fd); fputc('0',fd); fputc('A',fd);

enum {ETX=3};
fputc('2',fd); fputc('B',fd); fputc(ETX,fd); fputc('0',fd); fputc('A',fd);

fprintf(fd,"2B\x03" "0A");

#define ETX "\x03"
fprintf(fd,"2B" ETX "0A");

enum {ETX=3};
fprintf(fd,"2B%c0A",ETX);

You can sometmes #define strings that make commands and let the
compiler paste them together.
#define ESC "\x1B"
#define BEGIN_ROLE ESC "char("
#define END_ROLE ")"
#define ARTICHOKE_MODE BEGIN_ROLE "poor little artie" END_ROLE
#define CLOTHES_MODE ESC "clothes;"
#define CLOSE "\x18"
printf(
CLOSE "B" CLOTHES_MODE
CLOSE ARTICHOKE_MODE
"\nWhy he's just a rainbow!\n");

 

[Mike Wahler]

This will write two characters to 'fd':
'2' and '\0'. Is that what you wanted?

No it won't. The \0 of the string literal "2" terminates the
format -- otherwise -every- printf and fprintf would put in the
extra \0.[/QUOTE]

Oops, you're right; I was thinking of 'sprintf()'.

-Mike

 

[Peter Shaggy Haywood]

Groovy hepcat Mike Wahler was jivin' on Sat, 21 Oct 2006 02:24:39 GMT
in comp.lang.c.
Re: how to print ASCII "ETX" character?'s a cool scene! Dig it!

Oops, you're right; I was thinking of 'sprintf()'.

No you weren't, because that does the same thing as fprintf(), but
sending its output to memory rather than a file.

--

Dig the even newer still, yet more improved, sig!

http://alphalink.com.au/~phaywood/
"Ain't I'm a dog?" - Ronny Self, Ain't I'm a Dog, written by G. Sherry & W. Walker.
I know it's not "technically correct" English; but since when was rock & roll "technically correct"?

 

[Peter Shaggy Haywood]

Groovy hepcat Peter "Shaggy" Haywood was jivin' on Tue, 24 Oct 2006
03:53:53 GMT in comp.lang.c.
Re: how to print ASCII "ETX" character?'s a cool scene! Dig it!

Groovy hepcat Mike Wahler was jivin' on Sat, 21 Oct 2006 02:24:39 GMT
in comp.lang.c.
Re: how to print ASCII "ETX" character?'s a cool scene! Dig it!


No you weren't, because that does the same thing as fprintf(), but
sending its output to memory rather than a file.

Of course, it does store a '\0' at the end. So perhaps you were
thinking of sprintf() after all.

--

Dig the even newer still, yet more improved, sig!

http://alphalink.com.au/~phaywood/
"Ain't I'm a dog?" - Ronny Self, Ain't I'm a Dog, written by G. Sherry & W. Walker.
I know it's not "technically correct" English; but since when was rock & roll "technically correct"?