case:__LINE__ problem

[khaldoun KASSEM]

Hi


I have the folowing in my code:
#define crReturn(z) \
do {\
crLine=__LINE__; return (z); case __LINE__:;\
} while (0)

and when I call crReturn(z) in my program I get an error:
D:\SSH.C(707) : error C2051: case expression not constant

how can I solve this problem.
i use visual C++ 6.0
thank you

[zdf]

Strange code!

The syntax for case statements is:
case constant-expression: statement

__LINE__ should be a decimal integer constant.

Therefore the code should be almost ok (you’ll get warnings, I reckon). It must be a compiler bug.

Could you give an example of how you intend to use it?

Regards,

[cup]

It looks like some debugging code for tracing line numbers.

1) case is only allowed in switch statements. Since there isn't a switch statement surrounding the case, it is not valid code

2) The code after return cannot be reached.

3) The do-while loop is not necessary either. This style of the do-while loop is normally used by coders who don't like else if. They always seem extremely chuffed that they have 'discovered' this. Something I never really understood. They code

if (a)
...
else if (b)
....
else if (c)
....
else
....

as

do {
if (a) { ... ; break; }
if (b) { ... ; break; }
if (c) { ... ; break; }
...
} while (0);

[cup]

Just got this from the VC++ forum

#define crBegin1 static int crLine = 0;
#define crBegin2 switch(crLine) { case 0:;
#define crBegin crBegin1; crBegin2;
#define crFinish(z) } crLine = 0; return (z)
#define crFinishV } crLine = 0; return
#define crReturn(z) \
do {\
crLine=__LINE__; return (z); case __LINE__:;\
} while (0)
#define crReturnV \
do {\
crLine=__LINE__; return; case __LINE__:;\
} while (0)

and in the main() he do:

crBegin;

next_packet:

pktin.type = 0;
pktin.length = 0;

for (st->i = st->len = 0; st->i < 4; st->i++) {
while ((*datalen) == 0)
crReturn(4 - st->i);


My first comment is that coding like this in macros is never a good idea. Why the code is written to switch on the current line number is beyond me. Anyway, it expands to

static int crLine = 0;
switch(crLine)
{
case 0:;

next_packet:

pktin.type = 0;
pktin.length = 0;

for (st->i = st->len = 0; st->i < 4; st->i++)
{
while ((*datalen) == 0)
do {
crLine=__LINE__;
return (4-st->i);
case __LINE__:;
} while (0);


I think it is incomplete and there are lots of unreachable sections. Are you sure you are supposed to use this?

[zdf]

Following is the code I have tested on VC++. Unfortunately it is the only compiler I have so I cannot crosscheck.


int main(int argc, char* argv[])
{
int n = 1;
switch( n )
{
case __LINE__:
return 1;
default:
return 2;
}
}


Regards,

[Graham]

Anyone that comes up with code like that has much more serious problems than a "case expression is not constant" error.

[khaldoun KASSEM]

thank to all the code works very well

khaldoun

[zdf]

Originally posted by khaldoun KASSEM

thank you because you tried to help.
I solved the problem, it was a bug in visual C++, I just changed the compiler setting from "Program Database for Edit and Continue' to "Program Database" and the code works very well

thank you again

khaldoun

Thanks, I've learned something new.

[cbarnes]

In case your wondering what that code does - it does co-routines:

http://www.linuxhowtos.org/C_C++/coroutines.htm

Craig

[rachmann]

Your code?

Your code?

This code snippet is a copy right out of PuTTy...

Shame on you.

[JohnW@Wessex]

In case your wondering what that code does - it does co-routines:I read the article. All I can say is, if I saw code like that here I would have to nip round and borrow Graham's rubber chicken and engage in a little 'coder refactoring'!