K&R2 section 1.5.1 - "getchar" problem

[arnuld]

i have slightly modified the programme from section 1.5.1 which takes
the input frm keyboard and then prints that to the terminal. it just
does not run and i am unable to understand the error message.

may you tell me what is wrong and how to make that right ?

------------------------------ INPUT ---------------------
#include <stdio.h>

int main() {
int c;

while((c = getchar()) != EOF)
{
printf("your input: ");
putchar(c);
printf("\n");
}

return 0;
}

--------------------- OUTPUT -----------------------------
[arch@voodo kr2]$ gcc -ansi -pedantic -Wall -Wextra 151.c
151.c:1: error: expected identifier or '(' before '/' token
151.c:2:12: error: too many decimal points in number
In file included from /usr/include/_G_config.h:44,
from /usr/include/libio.h:32,
from /usr/include/stdio.h:72,
from 151.c:4:
/usr/include/gconv.h:72: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:88: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:97: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:174: error: expected specifier-qualifier-list
before 'size_t'
In file included from /usr/include/stdio.h:72,
from 151.c:4:
/usr/include/libio.h:328: error: expected specifier-qualifier-list
before 'size_t'
/usr/include/libio.h:360: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/libio.h:369: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/libio.h:485: error: expected '=', ',', ';', 'asm' or
'__attribute__' before '_IO_sgetn'
In file included from 151.c:4:
/usr/include/stdio.h:306: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/stdio.h:608: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'fread'
/usr/include/stdio.h:614: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'fwrite'
[arch@voodo kr2]$

 

[Sheth Raxit]

i have slightly modified the programme from section 1.5.1 which takes
the input frm keyboard and then prints that to the terminal. it just
does not run and i am unable to understand the error message.

may you tell me what is wrong and how to make that right ?

refer this link,
http://gcc.gnu.org/ml/gcc/2005-03/msg00865.html

if its match with your configuration (OS+compiler+libs+headers) apply
latest patch or do needful.

------------------------------ INPUT ---------------------
#include <stdio.h>

int main() {
int c;

while((c = getchar()) != EOF)
{
printf("your input: ");
putchar(c);
printf("\n");
}

return 0;

}

--------------------- OUTPUT -----------------------------
[arch@voodo kr2]$ gcc -ansi -pedantic -Wall -Wextra 151.c

I dont think -Wextra needed (or it is there) after -Wall

151.c:1: error: expected identifier or '(' before '/' token
151.c:2:12: error: too many decimal points in number
In file included from /usr/include/_G_config.h:44,
from /usr/include/libio.h:32,
from /usr/include/stdio.h:72,
from 151.c:4:
/usr/include/gconv.h:72: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:88: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:97: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:174: error: expected specifier-qualifier-list
before 'size_t'
In file included from /usr/include/stdio.h:72,
from 151.c:4:
/usr/include/libio.h:328: error: expected specifier-qualifier-list
before 'size_t'
/usr/include/libio.h:360: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/libio.h:369: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/libio.h:485: error: expected '=', ',', ';', 'asm' or
'__attribute__' before '_IO_sgetn'
In file included from 151.c:4:
/usr/include/stdio.h:306: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/stdio.h:608: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'fread'
/usr/include/stdio.h:614: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'fwrite'
[arch@voodo kr2]$

posted to gcc.gnu.help so u may got more help from other people.

Its failed telling
"Google Groups does not currently support posting to the following
usenet groups: "gcc.gnu.help" " but you may try there.




--Raxit Sheth

 

[Zhou Yan]

i have slightly modified the programme from section 1.5.1 which takes
the input frm keyboard and then prints that to the terminal. it just
does not run and i am unable to understand the error message.

may you tell me what is wrong and how to make that right ?

------------------------------ INPUT ---------------------
#include <stdio.h>

int main() {
int c;

while((c = getchar()) != EOF)
{
printf("your input: ");
putchar(c);
printf("\n");
}

return 0;
}

--------------------- OUTPUT -----------------------------
[arch@voodo kr2]$ gcc -ansi -pedantic -Wall -Wextra 151.c
151.c:1: error: expected identifier or '(' before '/' token
151.c:2:12: error: too many decimal points in number
In file included from /usr/include/_G_config.h:44,
from /usr/include/libio.h:32,
from /usr/include/stdio.h:72,
from 151.c:4:
/usr/include/gconv.h:72: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:88: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:97: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/gconv.h:174: error: expected specifier-qualifier-list
before 'size_t'
In file included from /usr/include/stdio.h:72,
from 151.c:4:
/usr/include/libio.h:328: error: expected specifier-qualifier-list
before 'size_t'
/usr/include/libio.h:360: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/libio.h:369: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/libio.h:485: error: expected '=', ',', ';', 'asm' or
'__attribute__' before '_IO_sgetn'
In file included from 151.c:4:
/usr/include/stdio.h:306: error: expected declaration specifiers or
'...' before 'size_t'
/usr/include/stdio.h:608: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'fread'
/usr/include/stdio.h:614: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'fwrite'
[arch@voodo kr2]$

I just tried your program, no problem...are you sure you are post
exactly what you input?

 

[Keith Thompson]

i have slightly modified the programme from section 1.5.1 which takes
the input frm keyboard and then prints that to the terminal. it just
does not run and i am unable to understand the error message.

may you tell me what is wrong and how to make that right ?

------------------------------ INPUT ---------------------
#include <stdio.h>

int main() {
int c;

while((c = getchar()) != EOF)
{
printf("your input: ");
putchar(c);
printf("\n");
}

return 0;
}

--------------------- OUTPUT -----------------------------
[arch@voodo kr2]$ gcc -ansi -pedantic -Wall -Wextra 151.c
151.c:1: error: expected identifier or '(' before '/' token
151.c:2:12: error: too many decimal points in number

[more error messages snipped]

When I compile your program with the same options, it compiles without
errors or warnings and works properly. Probably your <stdio.h> header
is messed up and/or your compiler is misconfigured.

I'm assuming the code you posted is exactly what you compiled
(copy-and-pasted, not re-typed).

Try compiling a C source file consisting only of a single line:

#include <stdio.h>

You'll probably see the same problem.

If I'm right, this is a question for gnu.gcc.help. Be sure to tell
them the details of your system (what operating system, what version
of gcc, and how gcc was installed); such details are usually off-topic
here, but often vital in tracking down a compiler-specific problem.

 

[arnuld]

When I compile your program with the same options, it compiles without
errors or warnings and works properly. Probably your <stdio.h> header
is messed up and/or your compiler is misconfigured.

I'm assuming the code you posted is exactly what you compiled
(copy-and-pasted, not re-typed).

YES, i did copy-paste.

Try compiling a C source file consisting only of a single line:

#include <stdio.h>
You'll probably see the same problem.

no trouble with that.

If I'm right, this is a question for gnu.gcc.help. Be sure to tell
them the details of your system (what operating system, what version
of gcc, and how gcc was installed); such details are usually off-topic
here, but often vital in tracking down a compiler-specific problem.

i do not know BUT this time, i *copied* the programme from my *post*
here to *emacs* and it worked, i do not how. this is th output:


[arch@voodo kr2]$ ./a.out
a
your input: a
your input:

b
your input: b
your input:

[arch@voodo kr2]$



why i am getting "your input" 2 times, instead of one ?

 

[Keith Thompson]

posted to gcc.gnu.help so u may got more help from other people.

Its failed telling
"Google Groups does not currently support posting to the following
usenet groups: "gcc.gnu.help" " but you may try there.

It's gnu.gcc.help, not gcc.gnu.help.

Please don't use silly abbreviations like "u". This isn't a chat
room.

 

[Keith Thompson]

YES, i did copy-paste.




no trouble with that.




i do not know BUT this time, i *copied* the programme from my *post*
here to *emacs* and it worked, i do not how. this is th output:

The only thing I can think of is that your source file originally
contained some funny characters. If you still have the original file,
try "cat -A" or "cat -v" to display any control characters.

[arch@voodo kr2]$ ./a.out
a
your input: a
your input:

b
your input: b
your input:

[arch@voodo kr2]$



why i am getting "your input" 2 times, instead of one ?

Let me guess. You typed a letter 'a', then hit the return key.
That's two characters.

Don't quote signatures unless you're commenting on them. (You've been
posting here long enough to know that.)

 

[arnuld]

The only thing I can think of is that your source file originally
contained some funny characters.

yes, it did contain some *funny* characters. actually they were at the
beginning of programme. they look like:

// K&R2 section 1.5.1
//

i was writing C++ in C

now i see compiler *did* mention that:

151.c:1: error: expected identifier or '(' before '/' token

[arch@voodo kr2]$ ./a.out
a
your input: a
your input:

b
your input: b
your input:

[arch@voodo kr2]$

why i am getting "your input" 2 times, instead of one ?

Let me guess. You typed a letter 'a', then hit the return key.
That's two characters.

NO, i am not talking about characters. i am talking about "words":
your input

after getchar(), there must be one sentence:

"your input: a"


but i get 2 sentences. 2nd one is:

"your input: "


why so ? (when i have used it once only in programme)

Don't quote signatures unless you're commenting on them. (You've been
posting here long enough to know that.)

sorry.

BTW, that was an accident, happened because i was careless.

 

[Keith Thompson]

yes, it did contain some *funny* characters. actually they were at the
beginning of programme. they look like:

// K&R2 section 1.5.1
//

i was writing C++ in C

"//" comments are also allowed in C99, and gcc accepts them as an
extension in certain modes. With the options you used, it doesn't
recognize them.

The lesson: copy-and-paste the entire source file. If you fed it to
the compiler, we need to see it.

[...]

[arch@voodo kr2]$ ./a.out
a
your input: a
your input:

b
your input: b
your input:

[arch@voodo kr2]$

why i am getting "your input" 2 times, instead of one ?

Let me guess. You typed a letter 'a', then hit the return key.
That's two characters.

NO, i am not talking about characters. i am talking about "words":
your input

after getchar(), there must be one sentence:

"your input: a"


but i get 2 sentences. 2nd one is:

"your input: "


why so ? (when i have used it once only in programme)

[...]

Here's your program (with the invalid comments deleted):

#include <stdio.h>

int main() {
int c;

while((c = getchar()) != EOF)
{
printf("your input: ");
putchar(c);
printf("\n");
}

return 0;
}

You call getchar() in a loop. The loop, which includes printing the
message "your input: ", will be executed once for each input
character. You typed a total of 4 characters: 'a', newline, 'b',
newline. The "putchar(c)" statement printed the value of each one;
when it prints a newline, it produces a blank line in your output.

I advised you in another thread to read section 12 of the comp.lang.c
FAQ. Please do so before posting more questions.

 

[Nick Keighley]

It would help if you left in more context (eg. the program...)

yes, it did contain some *funny* characters. actually they were at the
beginning of programme. they look like:

// K&R2 section 1.5.1
//

so you *didn't* post your exact code.

i was writing C++ in C

bad idea with a C compiler

now i see compiler *did* mention that:

151.c:1: error: expected identifier or '(' before '/' token

compilers do their best to tell you what the problem is

[arch@voodo kr2]$ ./a.out
a
your input: a
your input:

b
your input: b
your input:

[arch@voodo kr2]$

why i am getting "your input" 2 times, instead of one ?

Let me guess. You typed a letter 'a', then hit the return key.
That's two characters.

NO, i am not talking about characters.

well you should be. Your code was similar to this

while ((c = getchar()) != EOF)
printf ("your input %c\n", c);

so it keeps printing the line "your input..." until it gets an EOF.
You typed two characters ('a' and '\n') that weren't EOF, hence
two lines of output. (ok, technically, EOF isn't a character...)

 

[santosh]

yes, it did contain some *funny* characters. actually they were at the
beginning of programme. they look like:

// K&R2 section 1.5.1
//

i was writing C++ in C

Impossible. You were trying to feed the compiler C99 features while
telling it to stick to strict C89.

[ ... ]

[arch@voodo kr2]$ ./a.out
a
your input: a
your input:

b
your input: b
your input:

[arch@voodo kr2]$

why i am getting "your input" 2 times, instead of one ?

Let me guess. You typed a letter 'a', then hit the return key.
That's two characters.

NO, i am not talking about characters. i am talking about "words":
your input

after getchar(), there must be one sentence:

"your input: a"


but i get 2 sentences. 2nd one is:

"your input: "


why so ? (when i have used it once only in programme)

When you type in normal characters through the keyboard, under line
buffered systems, (which happens to be almost all operating systems),
you need to press the Return or Enter key to signal that your input
can be processed. The Enter key also generates a perfectly ordinary
value, (or values), like all other keys do. So your program is
actually receiving the value of 'a' followed by the value for '\n',
(which is C's representation of the system's end-of-line sequence,
which is itself generated by pressing the Return or Enter key.)

Both key values, ('a' and '\n'), are stored into the C library's
internal buffer for stdin stream. getchar goes and retrieves the top
character of the buffer, ('a'), and your loop prints it, followed by
your newline. The next iteration of loop calls getchar once again. You
_meant_ it to block for fresh input from the keyboard. But the '\n' is
still sitting in the internal buffer, and in C, it's a perfectly valid
character, which getchar retrieves and you print once again, as a
seemingly empty statement, but if you observe closely, you'll spot an
extra blank line. That's the effect of printing the '\n' character.

This "issue" confuses many a newbie. Sometimes this behaviour of the
stdio functions is expected, sometimes it's an annoyance. If you don't
want this behaviour you'll have to "read" and discard the remaining
characters in the internal buffer uptil, and including, the next
newline. You can do it through a simple while loop and wrap it up in a
function named, say, consume_line or something.

 

[arnuld]

Impossible. You were trying to feed the compiler C99 features while
telling it to stick to strict C89.

which one is a good practice: C99 or C89 ?

if it is C99 then just tell what options of "gcc" on Linux make it C99
compliant.

When you type in normal characters through the keyboard, under line
buffered systems, (which happens to be almost all operating systems),
you need to press the Return or Enter key to signal that your input
can be processed. The Enter key also generates a perfectly ordinary
value, (or values), like all other keys do. So your program is
actually receiving the value of 'a' followed by the value for '\n',
(which is C's representation of the system's end-of-line sequence,
which is itself generated by pressing the Return or Enter key.)

Both key values, ('a' and '\n'), are stored into the C library's
internal buffer for stdin stream. getchar goes and retrieves the top
character of the buffer, ('a'), and your loop prints it, followed by
your newline. The next iteration of loop calls getchar once again. You
_meant_ it to block for fresh input from the keyboard. But the '\n' is
still sitting in the internal buffer, and in C, it's a perfectly valid
character, which getchar retrieves and you print once again, as a
seemingly empty statement, but if you observe closely, you'll spot an
extra blank line. That's the effect of printing the '\n' character.

This "issue" confuses many a newbie. Sometimes this behaviour of the
stdio functions is expected, sometimes it's an annoyance. If you don't
want this behaviour you'll have to "read" and discard the remaining
characters in the internal buffer uptil, and including, the next
newline. You can do it through a simple while loop and wrap it up in a
function named, say, consume_line or something.

thanks for the pretty long explanation

 

[santosh]

which one is a good practice: C99 or C89 ?

Anyone. The core language hasn't changed all that much. The constructs
that've been added are not likely to be used at a beginner level. If
your compiler and standard library has acceptable amount of C99
coverage, and you're aware of the possibility of your code not working
with other implementations, then there's nothing wrong in learning C99
features. It is, after all, the current Standard for C.

if it is C99 then just tell what options of "gcc" on Linux make it C99
compliant.

First off gcc isn't yet fully C99 compliant, though it's getting there
faster than some other compilers.

The -std=c99 and -pedantic options can be used. Also you might want to
always use the -Wall and -Wextra options for maximum diagnostic
output. The manual for gcc has lots of interesting information you can
use to tailor gcc's behaviour for your use. Invoke 'info gcc'.

 

[arnuld]

Anyone. The core language hasn't changed all that much. The constructs
that've been added are not likely to be used at a beginner level. If
your compiler and standard library has acceptable amount of C99
coverage, and you're aware of the possibility of your code not working
with other implementations, then there's nothing wrong in learning C99
features. It is, after all, the current Standard for C.


First off gcc isn't yet fully C99 compliant, though it's getting there
faster than some other compilers.

i did not know that.

The -std=c99 and -pedantic options can be used. Also you might want to
always use the -Wall and -Wextra options for maximum diagnostic
output. The manual for gcc has lots of interesting information you can
use to tailor gcc's behaviour for your use. Invoke 'info gcc'.

thanks buddy

;-)

 

[Beej Jorgensen]

which one is a good practice: C99 or C89 ?

C99 isn't entirely widespread yet, so that might be a problem for
portability. Personally, I don't shy away from it.

You should at least know about the new features in C99 so you don't end
up doing things like this:

int restrict = 1;

if it is C99 then just tell what options of "gcc" on Linux make it C99
compliant.

http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/C-Dialect-Options.html

Check out "-std=".

gcc isn't fully compliant yet. Here's a link with the details:

http://gcc.gnu.org/gcc-4.1/c99status.html

-Beej