I am having a problem with some preprocessor constant value checking:
header.h:
#define MY_CONSTANT 1
file.c
#if MY_CONSTANTTT == 1 // <- note the typo!!
// dostuff...
#endif
I have always thought that C-compiler should give error message of
that, because the constant name "MY_CONSTAN TTT" doesn't exist.
However,
I got no error message with the line (Tested with MS Visual C++ 6.0
and
with one emdedded system compiler, no other compilers available now).
What I am trying to achieve is to define some product features which
should be included to compilation, in common header file. Usually this
is done with #define USE_FEATURE_XXX . But if programmer writes
"USE_FEATURE_XX X" incorrectly in C source, the code is not
included in compilation, but no error message is got. Example:
#ifdef USE_FEATURE_X // <-typo
// do something
#endif
I am trying to catch possible typing error with this "#if
USE_FEATURE_XXX == 1"
syntax, but it seems not to be working. Have I misunderstood C
standard, or are the compilers I use non-standard?
BR,
Timo
5  1798 
Timo <t_**********@y ahoo.com> scribbled the following: I am having a problem with some preprocessor constant value checking:
header.h:
#define MY_CONSTANT 1
file.c
#if MY_CONSTANTTT == 1 // <- note the typo!!
// dostuff...
#endif
I have always thought that C-compiler should give error message of
that, because the constant name "MY_CONSTAN TTT" doesn't exist.
However,
I got no error message with the line (Tested with MS Visual C++ 6.0
and
with one emdedded system compiler, no other compilers available now).
Yes, this is perfectly standard. The #if directive considers
nonexistent macro names as equal to 0, AFAIK.
What I am trying to achieve is to define some product features which
should be included to compilation, in common header file. Usually this
is done with #define USE_FEATURE_XXX . But if programmer writes
"USE_FEATURE_XX X" incorrectly in C source, the code is not
included in compilation, but no error message is got. Example:
#ifdef USE_FEATURE_X // <-typo
// do something
#endif
I am trying to catch possible typing error with this "#if
USE_FEATURE_XXX == 1"
syntax, but it seems not to be working. Have I misunderstood C
standard, or are the compilers I use non-standard?
You have misunderstood C standard. I don't know (yet) of any way of
doing what you want, but with some preprocessing trickery it might be
possible.
--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ---------------------------\
| Kingpriest of "The Flying Lemon Tree" G++ FR FW+ M- #108 D+ ADA N+++|
| http://www.helsinki.fi/~palaste W++ B OP+ |
\----------------------------------------- Finland rules! ------------/
"C++ looks like line noise."
- Fred L. Baube III
Timo wrote: #define MY_CONSTANT 1
file.c
#if MY_CONSTANTTT == 1 // <- note the typo!!
// dostuff...
#endif
I have always thought that C-compiler should give error message of
that, because the constant name "MY_CONSTAN TTT" doesn't exist.
Undefined identifiers in an "#if" directive are replaced with "0".
Jeremy.
Timo wrote:
I am having a problem with some preprocessor constant value checking:
header.h:
#define MY_CONSTANT 1
file.c
#if MY_CONSTANTTT == 1 // ?- note the typo!!
// dostuff...
#endif
I have always thought that C-compiler should give error message of
that, because the constant name "MY_CONSTAN TTT" doesn't exist.
However,
I got no error message with the line (Tested with MS Visual C++ 6.0
and
with one emdedded system compiler, no other compilers available now).
What I am trying to achieve is to define some product features which
should be included to compilation, in common header file. Usually this
is done with #define USE_FEATURE_XXX . But if programmer writes
"USE_FEATURE_XX X" incorrectly in C source, the code is not
included in compilation, but no error message is got. Example:
#ifdef USE_FEATURE_X // ?-typo
// do something
#endif
I am trying to catch possible typing error with this "#if
USE_FEATURE_XXX == 1"
syntax, but it seems not to be working. Have I misunderstood C
standard, or are the compilers I use non-standard?
BR,
Timo
The precompiler does not distinguiush between symbols defined in the
current file (or any #include'd file) and defined environment variables.
Thus there is no way for it to know that you have made a typo.
For example, if you typed "export MY_CONSTANTTT=1 " in the command line,
then compiled your program, the block delimited by "#if MY_CONSTANTTT ==
1 " would be compiled.
--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Common User Interface Services
M/S 2R-94 (206)544-5225
On Fri, 3 Oct 2003, Fred L. Kleinschmidt wrote:
Timo wrote:
#if MY_CONSTANTTT == 1 // ?- note the typo!!
The precompiler does not distinguiush between symbols defined in the
current file (or any #include'd file) and defined environment variables.
Thus there is no way for it to know that you have made a typo.
For example, if you typed "export MY_CONSTANTTT=1 " in the command line,
then compiled your program, the block delimited by "#if MY_CONSTANTTT ==
1 " would be compiled.
That's one of the more bizarre incorrect explanations I've heard
here in a while. At first, I didn't even recognize the context;
I thought Fred was giving a Lisp-environment answer in the wrong
newsgroup or something. (Then a few seconds later I realized he
was probably using a proprietary compiler on a (proprietary?)
*nix system with 'export' being an OS shell command.)
'export' is not a feature of the C language.
--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Hoo, dear.
-Arthur
Arthur J. O'Dwyer wrote:
On Fri, 3 Oct 2003, Fred L. Kleinschmidt wrote:
Timo wrote: >
> #if MY_CONSTANTTT == 1 // ?- note the typo!!
The precompiler does not distinguiush between symbols defined in the
current file (or any #include'd file) and defined environment variables.
Thus there is no way for it to know that you have made a typo.
For example, if you typed "export MY_CONSTANTTT=1 " in the command line,
then compiled your program, the block delimited by "#if MY_CONSTANTTT ==
1 " would be compiled.
That's one of the more bizarre incorrect explanations I've heard
here in a while. At first, I didn't even recognize the context;
I thought Fred was giving a Lisp-environment answer in the wrong
newsgroup or something. (Then a few seconds later I realized he
was probably using a proprietary compiler on a (proprietary?)
*nix system with 'export' being an OS shell command.)
'export' is not a feature of the C language.
Not only is it bizzare... It would probably drive me crazy (perhaps, because
I've never used such a weird system ever). Talk about compiler messages
that make you lose your hair fast, such an environment would just be loaded
with them. As a matter of self-defense, I ask the OP to reveal the system
under consideration, so I can keep a safe distance.
-nrk. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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