#define can't be inside function?

[Bryan Parkoff]

"#define" can only be inside the global scope before main() function.
"#if" can be tested after "#define" is executed. The problem is that
"#define" can't be inside main() function. I do not wish to create multiple
functions which they look almost identical in C++ source code. The C++
compiler should be able to compile one Test() function into two almost
identical functions before they are translated into the machine language
object. The machine language object has two Test() functions, but they
exclude some line parts. First Test() function uses printf("1\n") and
second Test() function uses printf("2\n").
It is the same example that you use MACRO to test the conditional
defines before some lines can be inserted or removed.
If there is no way to test it at compile time, I would have to manual
pasting one Test() function into multiple Test() functions in C++ source
code. Please advise.

Bryan Parkoff

#include <stdio.h>

#define A 1

void Test(void)
{
#if (A == 1)
printf("1\n");
#endif

#if (A == 2)
printf("2\n");
#endif
}

int main(void)
{
Test();
#undef A
#define A 2
Test();

return 0;
}

[Peter Koch Larsen]

"Bryan Parkoff" <no****@nospam. com> skrev i en meddelelse
news:qd******** *****@newssvr11 .news.prodigy.c om...

"#define" can only be inside the global scope before main() function.
This is wrong. #defines can be placed everywhere - it just has to be on a
line by itself (with "#" being the first character of that line).
"#if" can be tested after "#define" is executed. The problem is that
"#define" can't be inside main() function. I do not wish to create
multiple functions which they look almost identical in C++ source code.
The C++ compiler should be able to compile one Test() function into two
almost identical functions before they are translated into the machine
language object. The machine language object has two Test() functions,
but they exclude some line parts. First Test() function uses
printf("1\n") and second Test() function uses printf("2\n").
It is the same example that you use MACRO to test the conditional
defines before some lines can be inserted or removed.
If there is no way to test it at compile time, I would have to manual
pasting one Test() function into multiple Test() functions in C++ source
code. Please advise.

Bryan Parkoff

[snip]

/Peter

[roberth+news]

Bryan Parkoff <no****@nospam. com> wrote:
| "#define" can only be inside the global scope before main() function.
| "#if" can be tested after "#define" is executed. The problem is that
| "#define" can't be inside main() function. I do not wish to create multiple
| functions which they look almost identical in C++ source code. The C++
| compiler should be able to compile one Test() function into two almost
| identical functions before they are translated into the machine language
| object. The machine language object has two Test() functions, but they
| exclude some line parts. First Test() function uses printf("1\n") and
| second Test() function uses printf("2\n").

That's what templates are for:
template <int a>
void foo()
{
if (a == 1)
printf("1\n");
if (a == 2)
printf("2\n");
}

int main()
{
foo<1>();
foo<2>();
}

| It is the same example that you use MACRO to test the conditional
| defines before some lines can be inserted or removed.

You could of course use some form of macro magic, but templates are
usually prettier.

| If there is no way to test it at compile time, I would have to manual
| pasting one Test() function into multiple Test() functions in C++ source
| code. Please advise.

Compilers today do such optimizations. My g++ do. Do you want to test
things at compile time or before compile time?

--
Robert Bauck Hamar

[Bryan Parkoff]

Robert Bauck Hamar,

I want to say thank you very much for the information. I try to add
comment so you can understand better. Please look at my example. It has
multiple functions. They are almost identical. Sometimes, I use B++, but
sometimes, I use C++. I do not wish to use Test1(), Test2(), and Test3(),
but I use one function as Test(). I expect that Test1(), Test2(), and
Test3() stop to exist in the source code. Please read second paragraph
below my example.

void Test(void)
{
A++;
B++;
C++;
}

void Test1(void)
{
A++;
}

void Test2(void)
{
A++;
B++;
}

void Test3(void)
{
A++;
C++;
}

If Test() contains "if (A == XX)", it should never exist in the machine
language object in both debug version and release version. I expect C++
compiler to remove "if (A == XX)" before A++, B++, and/or C++ can be stored
in the machine language object. Look at my example below. Please read
third paragraph below my example.

int main(void)
{
A = 1;
Test(); // Put A++ only (B++ and C++ are excluded) without "if (A ==
XX)"
A = 2;
Test(); // Put A++ and B++ only (C++ is excluded) without "if (A == XX)"
A = 3;
Test(); // Put A++ and C++ only (B++ is excluded) without "if (A == XX)"
A = 0;
Test(); // Put A++, B++, and C++ without "if (A == XX)"
}

void Test(void)
{
if (A == 1)
A++;
if (A == 2)
B++;
if (A == 3)
C++;
}

After my C++ source code is compiled into machine language object in
both debug version and release version, "if (A == XX)" is removed
automatically, A++, B++, and/or C++ can be preserved or removed. It would
reduce x86 instructions and improve performance.
I know that "if (A == XX)" do not work so it needs one or more variables
like "if (B == XX)" and "if (C == XX)" so they can test correctly.
Do you expect that template is only the answer?

Bryan Parkoff

<ro**********@i fi.uio.no> wrote in message
news:d7******** **@readme.uio.n o...

Bryan Parkoff <no****@nospam. com> wrote:
| "#define" can only be inside the global scope before main()
function.
| "#if" can be tested after "#define" is executed. The problem is that
| "#define" can't be inside main() function. I do not wish to create
multiple
| functions which they look almost identical in C++ source code. The C++
| compiler should be able to compile one Test() function into two almost
| identical functions before they are translated into the machine language
| object. The machine language object has two Test() functions, but they
| exclude some line parts. First Test() function uses printf("1\n") and
| second Test() function uses printf("2\n").

That's what templates are for:
template <int a>
void foo()
{
if (a == 1)
printf("1\n");
if (a == 2)
printf("2\n");
}

int main()
{
foo<1>();
foo<2>();
}

| It is the same example that you use MACRO to test the conditional
| defines before some lines can be inserted or removed.

You could of course use some form of macro magic, but templates are
usually prettier.

| If there is no way to test it at compile time, I would have to
manual
| pasting one Test() function into multiple Test() functions in C++ source
| code. Please advise.

Compilers today do such optimizations. My g++ do. Do you want to test
things at compile time or before compile time?

--
Robert Bauck Hamar

[Bryan Parkoff]

Robert Bauck Hamar,

I want to let you know that your example code does not work. If
template function reads "1" and "2", then it will execute "2" twice. It
never shows "1" before "2". Look at my example that is similiar yours.

#include <stdio.h>

template <int A>
void Test(void)
{
if (A == 1)
printf("1\n");
if (A == 2)
printf("2\n");
if (A == 3)
printf("3\n");
printf("\n");
}

int main(void)
{
Test<1>();
Test<2>();
Test<3>();

return 0;
}

Output shows "3" in first line, second line, and third line. Is there a
fix?

Bryan Parkoff
<ro**********@i fi.uio.no> wrote in message
news:d7******** **@readme.uio.n o...

Bryan Parkoff <no****@nospam. com> wrote:
| "#define" can only be inside the global scope before main()
function.
| "#if" can be tested after "#define" is executed. The problem is that
| "#define" can't be inside main() function. I do not wish to create
multiple
| functions which they look almost identical in C++ source code. The C++
| compiler should be able to compile one Test() function into two almost
| identical functions before they are translated into the machine language
| object. The machine language object has two Test() functions, but they
| exclude some line parts. First Test() function uses printf("1\n") and
| second Test() function uses printf("2\n").

That's what templates are for:
template <int a>
void foo()
{
if (a == 1)
printf("1\n");
if (a == 2)
printf("2\n");
}

int main()
{
foo<1>();
foo<2>();
}

| It is the same example that you use MACRO to test the conditional
| defines before some lines can be inserted or removed.

You could of course use some form of macro magic, but templates are
usually prettier.

| If there is no way to test it at compile time, I would have to
manual
| pasting one Test() function into multiple Test() functions in C++ source
| code. Please advise.

Compilers today do such optimizations. My g++ do. Do you want to test
things at compile time or before compile time?

--
Robert Bauck Hamar

[Jerry Coffin]

In article <qd************ *@newssvr11.new s.prodigy.com>,
no****@nospam.c om says...

"#define" can only be inside the global scope before main() function.
"#if" can be tested after "#define" is executed. The problem is that
"#define" can't be inside main() function.
What makes you think that? I'm not sure it does much (if anything) to
help the problem you cite below, but it's entirely possible to do a
#define inside of main (or another function of your choice).
I do not wish to create multiple
functions which they look almost identical in C++ source code.
Indeed -- one of the reasons for using functions is to avoid code
duplication.
#include <stdio.h>

#define A 1

void Test(void)
{
#if (A == 1)
printf("1\n");
#endif

#if (A == 2)
printf("2\n");
#endif
}

int main(void)
{
Test();
#undef A
#define A 2
Test();

return 0;
}

There are quite a few ways of handling this. The first (and most
obvious) would be to simply pass A as a parameter:

#define A 1

void Test(int A) {
printf("%d\n", A);
}

int main() {
Test(A); // prints 1

#undef A
#define A 2

Test(A); // prints 2

return 0;
}

If, for some reason, it's necessary that you print a string literal
instead of converting A from an int at run-time, you can do that with
the preprocessor:

#include <stdio.h>

#define make_string(a) #a
#define str(x) make_string(x)

#define Test(A) printf(str(A) "\n")

int main() {
#define A 1
Test(A);
#undef A
#define A 2
Test(A);
return 0;
}

The make_string(x)/str(x) is a fairly well-known pre-processor idiom.
The '#' is the pre-processor's stringizing operator, which produces a
quoted string literal of whatever it's applied to. The extra level of
macro expansion makes the preprocessor expand the parameter out to
its value instead of its name. Once we have the value in a string, we
put it next to the "\n" string, so the compiler will concatenate the
two into a single string for us.

If you really can't pass A as a parameter, you can do something like
this:

#include <stdio.h>

#define make_string(a) #a
#define str(x) make_string(x)

#define Test() printf(str(A) "\n")

int main() {
#define A 1
Test();
#undef A
#define A 2
Test();
return 0;
}

Personally, I'd advise against this though -- it usually loses far
more than it gains.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Bryan Parkoff]

Jerry,

Your previous example below does not work. It only prints "1" in first
line and second line. I can assume that "#undef A" and "#define A 2" are
not working.

#define A 1

void Test(int A) {
printf("%d\n", A);
}

int main() {
Test(A); // prints 1

#undef A
#define A 2

Test(A); // prints 2

return 0;
}

Bryan Parkoff

[Jerry Coffin]

In article <yI************ *@newssvr30.new s.prodigy.com>,
no****@nospam.c om says...

Jerry,

Your previous example below does not work. It only prints "1" in first
line and second line. I can assume that "#undef A" and "#define A 2" are
not working.

I think I must have accidentally copied and pasted the wrong version
-- as it stands right now, it doesn't even compile -- this:

#define A 1

void Test(int A) {
// ...

expands to:

void Test(int 1) {

which isn't allowed. Fixing that gives:

#include <stdio.h>

#define A 1

void Test(int a) {
printf("%d\n", a);
}

int main() {
Test(A); // prints 1

#undef A
#define A 2

Test(A); // prints 2

return 0;
}

which prints out:

1
2

as it should. If you're getting 1 twice as you describe above, then
I'd have to guess it's a problem with (the version of) whatever
compiler you're using.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Bryan Parkoff]

Jerry,

Yes, it still gets "1" twice. I use Microsoft Visual C++ 6.0. Do you
know if I should be able to fix this problem by using C++ Compiler's option?
Or...do you suggest me to use another C++ Compiler?

Bryan Parkoff

"Jerry Coffin" <jc*****@taeus. com> wrote in message
news:MP******** *************** *@news.sunsite. dk...

In article <yI************ *@newssvr30.new s.prodigy.com>,
no****@nospam.c om says...

Jerry,

Your previous example below does not work. It only prints "1" in
first
line and second line. I can assume that "#undef A" and "#define A 2" are
not working.

I think I must have accidentally copied and pasted the wrong version
-- as it stands right now, it doesn't even compile -- this:

#define A 1

void Test(int A) {
// ...

expands to:

void Test(int 1) {

which isn't allowed. Fixing that gives:

#include <stdio.h>

#define A 1

void Test(int a) {
printf("%d\n", a);
}

int main() {
Test(A); // prints 1

#undef A
#define A 2

Test(A); // prints 2

return 0;
}

which prints out:

1
2

as it should. If you're getting 1 twice as you describe above, then
I'd have to guess it's a problem with (the version of) whatever
compiler you're using.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Jerry Coffin]

In article <Z7************ **@newssvr30.ne ws.prodigy.com> ,
no****@nospam.c om says...

Jerry,

Yes, it still gets "1" twice. I use Microsoft Visual C++ 6.0. Do you
know if I should be able to fix this problem by using C++ Compiler's option?
Or...do you suggest me to use another C++ Compiler?

This seems very strange -- I originally tested it with VC++ 7.1, but
doing a quick check with 6.0, the result is identical. Just for fun,
I also tested it with Borland 5.5 and Comeau 4.3.4, all with
identical results.

Just for fun, let's try a little exercise. I've rewritten the code to
eliminate the header, and just declare printf directly -- generally a
poor idea, but helpful for the moment.

#define A 1

extern int printf(char const *, ...);

void Test(int a) {
printf("%d\n", a);
}

int main() {
Test(A); // prints 1

#undef A
#define A 2

Test(A); // prints 2

return 0;
}

Now, what we want to do is ONLY preprocess that code to see what it
produces. To do that, use cl /E whatever.c, and it'll display the
preprocessed output. That's why we got rid of stdio.h -- it will have
lots of extra "stuff" we don't care about that gets in the way of
seeing what we do care about. Here's the output I get:

#line 1 "ize.c"
extern int printf(char const *, ...);

void Test(int a) {
printf("%d\n", a);
}

int main() {
Test(1);


Test(2);

return 0;
}

One remote possibility occurs to me: what (if any) service pack have
you applied to Visual Studio? It's remotely possible that this got
fixed somewhere along the line, and you _could_ be running a version
from before its getting fixed. If so, simply applying the latest
service pack may suddenly make things work for you.

--
Later,
Jerry.

The universe is a figment of its own imagination.