Are C pitfalls the mistake of standard or that of implementations ?

[Greenhorn]

Hi,
We see that C is a bit liberal towards non-standard syntax,
for e.g. when i tried
<printf("string 1", "string2 %d", v1);> in Dev-C++, it printed string1
and no error was raised, is this the mistake of standard or the
implementation (Dev-C++).
I was under the impression that the implementations could have been
better by implementing proper rules and adhering to the standard (ANSI
C) at the same time, for e.g., in the above case i was assuming that
the standard would have specified something like "an implementation
MUST provide printf("string where % is special char..", var1,..);". Now
a good implementor could have implemented this along with an error chek
to see the user code strictly adheres to that format and raise an error
if not (my e.g., above).
But, many implementations , even popular ones don't seem to do this.
What do u opine? People who have read the actual Standard can throw
some light on the specification in the standard.

Greenhorn.

[Kenneth Bull]

Greenhorn wrote:

Hi,
We see that C is a bit liberal towards non-standard syntax,
for e.g. when i tried
<printf("string 1", "string2 %d", v1);> in Dev-C++, it printed string1
and no error was raised, is this the mistake of standard or the
implementation (Dev-C++).
I was under the impression that the implementations could have been
better by implementing proper rules and adhering to the standard (ANSI C) at the same time, for e.g., in the above case i was assuming that
the standard would have specified something like "an implementation
MUST provide printf("string where % is special char..", var1,..);". Now a good implementor could have implemented this along with an error chek to see the user code strictly adheres to that format and raise an error if not (my e.g., above).
But, many implementations , even popular ones don't seem to do this.
What do u opine? People who have read the actual Standard can throw
some light on the specification in the standard.

Greenhorn.

If you invoke undefined behaviour, any implementation can do anything
with your program. In others words "if you don't follow the rules,
anything can happen, and this 'anything' can be different for any
implementation"

[Walter Roberson]

In article <11************ **********@f14g 2000cwb.googleg roups.com>,
Greenhorn <te************ @yahoo.com> wrote:
: We see that C is a bit liberal towards non-standard syntax,
:for e.g. when i tried
:<printf("strin g1", "string2 %d", v1);> in Dev-C++, it printed string1
:and no error was raised, is this the mistake of standard or the
:implementation (Dev-C++).

Neither. There is no requirement in the definition of printf()
that all of the value arguments need to be "consumed" by the printf().

:I was under the impression that the implementations could have been
:better by implementing proper rules and adhering to the standard (ANSI
:C) at the same time, for e.g., in the above case i was assuming that
:the standard would have specified something like "an implementation
:MUST provide printf("string where % is special char..", var1,..);".

I don't understand that last bit. There is nothing in the standard
that requires that the first argument to printf() have a % format
specifier.

:Now
:a good implementor could have implemented this along with an error chek
:to see the user code strictly adheres to that format and raise an error
:if not (my e.g., above).

It isn't an error. Some compilers will warn about it, as will 'lint'.
--
If a troll and a half can hook a reader and a half in a posting and a half,
how many readers can six trolls hook in six postings?

[Ben Pfaff]

"Greenhorn" <te************ @yahoo.com> writes:

We see that C is a bit liberal towards non-standard syntax,
for e.g. when i tried
<printf("string 1", "string2 %d", v1);> in Dev-C++, it printed string1
and no error was raised, is this the mistake of standard or the
implementation (Dev-C++).

This is the correct behavior. It is usually a mistake, so better
C implementations will warn about it, if you turn on that
feature. GCC is an example of an implementation that will do so.
--
"When I have to rely on inadequacy, I prefer it to be my own."
--Richard Heathfield

[infobahn]

Walter Roberson wrote:

If a troll and a half can hook a reader and a half in a posting and a half,
how many readers can six trolls hook in six postings?

I make it 24. I stand ready to be corrected.

[Jonathan Bartlett]

Greenhorn wrote:

Hi,
We see that C is a bit liberal towards non-standard syntax,
for e.g. when i tried
<printf("string 1", "string2 %d", v1);> in Dev-C++, it printed string1
and no error was raised, is this the mistake of standard or the
implementation (Dev-C++).
I was under the impression that the implementations could have been
better by implementing proper rules and adhering to the standard (ANSI
C) at the same time, for e.g., in the above case i was assuming that
the standard would have specified something like "an implementation
MUST provide printf("string where % is special char..", var1,..);". Now
a good implementor could have implemented this along with an error chek
to see the user code strictly adheres to that format and raise an error
if not (my e.g., above).
But, many implementations , even popular ones don't seem to do this.
What do u opine? People who have read the actual Standard can throw
some light on the specification in the standard.

The issue is that the compiler can't necessarily see what you are
passing to printf, and it doesn't really care, either, as printf is a
library function and not an operator. Think of the following things:

1) the format string given to printf could also be a generated value, in
which case the compiler would not even be able to see what it is
2) printf is a library function, so someone could switch it out with
something that has different functionality, but the compiler wouldn't be
aware, and would generate errors even when there were none.
3) The call signature of printf is printf(char *format, ...). This
means that by its call signature, ANY number of parameters (except zero)
are LEGAL, even if the results aren't defined or useful. This is a
limitation of the C language, as this is a limitation of the way C
function prototypes work.

Jon
----
Learn to program using Linux assembly language
http://www.cafeshops.com/bartlettpublish.8640017

[infobahn]

Jonathan Bartlett wrote:

3) The call signature of printf is printf(char *format, ...).

Minor nit: const char *format

[Greenhorn]

I agree that any implementation can do anything, y not leverage on that
and try to raise warnings and errors when that is not expected in that
form. for e.g., i am guessing that ANSI standard doesn't say something
like "no errors are to be raised when printf("blah bhal.. is used".
which means an implementation can raise error (atleast a warning).
Ofcourse, some implementations use warnings as a proper tool.

Greenhorn

Kenneth Bull wrote:

Greenhorn wrote:

Hi,
We see that C is a bit liberal towards non-standard syntax,
for e.g. when i tried
<printf("string 1", "string2 %d", v1);> in Dev-C++, it printed string1 and no error was raised, is this the mistake of standard or the
implementation (Dev-C++).
I was under the impression that the implementations could have been
better by implementing proper rules and adhering to the standard

(ANSI

C) at the same time, for e.g., in the above case i was assuming that the standard would have specified something like "an implementation
MUST provide printf("string where % is special char..", var1,..);".

Now

a good implementor could have implemented this along with an error

chek

to see the user code strictly adheres to that format and raise an

error

if not (my e.g., above).
But, many implementations , even popular ones don't seem to do this.
What do u opine? People who have read the actual Standard can throw
some light on the specification in the standard.

Greenhorn.

If you invoke undefined behaviour, any implementation can do anything
with your program. In others words "if you don't follow the rules,
anything can happen, and this 'anything' can be different for any
implementation"

[Greenhorn]

I agree that any implementation can do anything, y not leverage on that
and try to raise warnings and errors when that is not expected, say in
an expression. For e.g., i am guessing that ANSI standard doesn't say
something like "no errors are to be raised when printf("blah bhal.. is
used" which means an implementation can raise error (atleast a
warning). Ofcourse, some implementations use warnings as a proper tool.

Greenhorn

Kenneth Bull wrote:

Greenhorn wrote:

Hi,
We see that C is a bit liberal towards non-standard syntax,
for e.g. when i tried
<printf("string 1", "string2 %d", v1);> in Dev-C++, it printed string1 and no error was raised, is this the mistake of standard or the
implementation (Dev-C++).
I was under the impression that the implementations could have been
better by implementing proper rules and adhering to the standard

(ANSI

C) at the same time, for e.g., in the above case i was assuming that the standard would have specified something like "an implementation
MUST provide printf("string where % is special char..", var1,..);".

Now

a good implementor could have implemented this along with an error

chek

to see the user code strictly adheres to that format and raise an

error

if not (my e.g., above).
But, many implementations , even popular ones don't seem to do this.
What do u opine? People who have read the actual Standard can throw
some light on the specification in the standard.

Greenhorn.

If you invoke undefined behaviour, any implementation can do anything
with your program. In others words "if you don't follow the rules,
anything can happen, and this 'anything' can be different for any
implementation"

[Greenhorn]

is it 6.