Declaring variables mid-function

Declaring variables mid-function

[Shawn]

    I am writing a medium sized program, and ran into a problem where gcc
would not compile any function that did not have all of its variables
declared as the first lines of the function.  As a test, I wrote this small
program:

int test(char *tst, char *tst2, char **tst3);
int test2(void);

int main()
{
 test2();

 char *tst;
 char *tst2;
 char *tst3;

 test(tst, tst2, &tst3);

 return 1;

}

int test(char *tst, char *tst2, char **tst3)
{
 return 21;
}

int test2(void)
{
 return 21;
}

When trying to compile this, seemingly simple program, gcc complains.  This
is the output:

bash-2.03$ gcc test.c -o test
test.c: In function `main':
test.c:8: parse error before `char'
test.c:12: `tst' undeclared (first use in this function)
test.c:12: (Each undeclareed identifier is reported only once
test.c:12: for each function it appears in.)
test.c:12: `tst2' undeclared (first use in this function)
test.c:12: `tst3' undeclared (first use in this function)

Does anybody have any idea what is going on here?  My system is a Pentium,
with 48 MB ram, running Slackware Linux 7.0, gcc version 2.91.66 (egcs).
Thank you in advance!

-Shawn

Re: Declaring variables mid-function

[llewelly]

On Sat, 18 Dec 1999, Shawn wrote:

>     I am writing a medium sized program, and ran into a problem where gcc
> would not compile any function that did not have all of its variables
> declared as the first lines of the function.  As a test, I wrote this small
> program:
> 

ANSI C requires that all variables be declared at the begining of the
  block.

> int test(char *tst, char *tst2, char **tst3);
> int test2(void);
> 
> int main()
> {
>  test2();
> 
>  char *tst;
>  char *tst2;
>  char *tst3;
> 
>  test(tst, tst2, &tst3);
> 
>  return 1;
> 
> }
> 
> int test(char *tst, char *tst2, char **tst3)
> {
>  return 21;
> }
> 
> int test2(void)
> {
>  return 21;
> }
> 
> When trying to compile this, seemingly simple program, gcc complains.  This
> is the output:
> 
> bash-2.03$ gcc test.c -o test
> test.c: In function `main':
> test.c:8: parse error before `char'
> test.c:12: `tst' undeclared (first use in this function)
> test.c:12: (Each undeclareed identifier is reported only once
> test.c:12: for each function it appears in.)
> test.c:12: `tst2' undeclared (first use in this function)
> test.c:12: `tst3' undeclared (first use in this function)

This is ANSI conformant behavior; any ANSI C compiler will give you
  similar errors.

> 
> Does anybody have any idea what is going on here?  My system is a Pentium,
> with 48 MB ram, running Slackware Linux 7.0, gcc version 2.91.66 (egcs).
> Thank you in advance!
> 

Perhaps you are too acustomed to C++. Unlike C, C++ *does* allow
  declaration of variables anywhere in a block. If you wish to code in 
  C++, compile your code with 'g++', as in: 'g++ test.c -o test' 

Your example compiles perfectly with g++; it is correct C++, but not
  correct C.

Re: Declaring variables mid-function

[llewelly]

On Sat, 18 Dec 1999, Shawn wrote:

>     I am writing a medium sized program, and ran into a problem where gcc
> would not compile any function that did not have all of its variables
> declared as the first lines of the function.  As a test, I wrote this small
> program:
> 

ANSI C requires that all variables be declared at the begining of the
  block.

> int test(char *tst, char *tst2, char **tst3);
> int test2(void);
> 
> int main()
> {
>  test2();
> 
>  char *tst;
>  char *tst2;
>  char *tst3;
> 
>  test(tst, tst2, &tst3);
> 
>  return 1;
> 
> }
> 
> int test(char *tst, char *tst2, char **tst3)
> {
>  return 21;
> }
> 
> int test2(void)
> {
>  return 21;
> }
> 
> When trying to compile this, seemingly simple program, gcc complains.  This
> is the output:
> 
> bash-2.03$ gcc test.c -o test
> test.c: In function `main':
> test.c:8: parse error before `char'
> test.c:12: `tst' undeclared (first use in this function)
> test.c:12: (Each undeclareed identifier is reported only once
> test.c:12: for each function it appears in.)
> test.c:12: `tst2' undeclared (first use in this function)
> test.c:12: `tst3' undeclared (first use in this function)

This is ANSI conformant behavior; any ANSI C compiler will give you
  similar errors.

> 
> Does anybody have any idea what is going on here?  My system is a Pentium,
> with 48 MB ram, running Slackware Linux 7.0, gcc version 2.91.66 (egcs).
> Thank you in advance!
> 

Perhaps you are too acustomed to C++. Unlike C, C++ *does* allow
  declaration of variables anywhere in a block. If you wish to code in 
  C++, compile your code with 'g++', as in: 'g++ test.c -o test' 

Your example compiles perfectly with g++; it is correct C++, but not
  correct C.

Re: Declaring variables mid-function

[Jamie Walker]

In article < 385c11fa@oit.umass.edu >, Shawn <NRLax27@aol.com> writes
>    I am writing a medium sized program, and ran into a problem where gcc
>would not compile any function that did not have all of its variables
>declared as the first lines of the function.  As a test, I wrote this small
>program:
In standard C, you cannot declare variables part-way through any
function.

Move them to the top of the function and they will compile fine.

C++ does support what you want, so you could rename your .c files to .C
and gcc will treat them as C++, then they should work fine.

HTH,
-- 
Jamie Walker                                  http://www.sagaxis.co.uk/
"lp1 reported invalid error status (on fire, eh?)", Linux error message
       PGP Key ID: 0x1B6BBB15 (available on public key servers)

Re: Declaring variables mid-function

[bowman]

Jamie Walker <jamie@sagaxis.co.uk> wrote:

>In standard C, you cannot declare variables part-way through any
>function.

I won't stick my neck out and say it is standard, as I don't have
Harbison & Steele handy, but gcc will accept declarations at the
head of any block. So

int foo() 
{
	int bar;
	bar = 1234;
	{
		int fubar;
		for (fubar=0; fubar<bar; fubar++)
			printf("completely fooed\n");
	}
}

should compile. I believe that fubar is at least lexically visible to the
end of the function, unlike some languages where the scope would be strictly
the block.

Comments from the language lawyers are welcome on what exactly the standard
stipulates are welcome.

Re: Declaring variables mid-function

[Brendan Murray]

> {
> int fubar;
> for (fubar=0; fubar<bar; fubar++)
> printf("completely fooed\n");
> }
> }
>
> should compile. I believe that fubar is at least lexically visible to the
> end of the function, unlike some languages where the scope would be
strictly
> the block.
>

Nope - once you hit the enclosing "}", fubar's toast. In C, variables have
scope only at the level in which they have been declared; in this case
that's within the block, not to the end of the function.

B=

Re: Declaring variables mid-function

[Brendan Murray]

> {
> int fubar;
> for (fubar=0; fubar<bar; fubar++)
> printf("completely fooed\n");
> }
> }
>
> should compile. I believe that fubar is at least lexically visible to the
> end of the function, unlike some languages where the scope would be
strictly
> the block.
>

Nope - once you hit the enclosing "}", fubar's toast. In C, variables have
scope only at the level in which they have been declared; in this case
that's within the block, not to the end of the function.

B=

Re: Declaring variables mid-function

[Arthur Gold]

bowman wrote:
> 
> Jamie Walker <jamie@sagaxis.co.uk> wrote:
> 
> >In standard C, you cannot declare variables part-way through any
> >function.
> 
> I won't stick my neck out and say it is standard, as I don't have
> Harbison & Steele handy, but gcc will accept declarations at the
> head of any block. So
> 
> int foo()
> {
>         int bar;
>         bar = 1234;
>         {
>                 int fubar;
>                 for (fubar=0; fubar<bar; fubar++)
>                         printf("completely fooed\n");
>         }
> }
> 
> should compile. I believe that fubar is at least lexically visible to the
> end of the function, unlike some languages where the scope would be strictly
> the block.
Nope. Strictly the block.

HTH,
--ag
> 
> Comments from the language lawyers are welcome on what exactly the standard
> stipulates are welcome.

-- 
Artie Gold, Austin, TX  (finger the cs.utexas.edu account for more info)
mailto:agold@bga.com or mailto:agold@cs.utexas.edu
--
A: Look for a lawyer who speaks Aramaic...about trademark infringement.

Re: Declaring variables mid-function

[Arthur Gold]

bowman wrote:
> 
> Jamie Walker <jamie@sagaxis.co.uk> wrote:
> 
> >In standard C, you cannot declare variables part-way through any
> >function.
> 
> I won't stick my neck out and say it is standard, as I don't have
> Harbison & Steele handy, but gcc will accept declarations at the
> head of any block. So
> 
> int foo()
> {
>         int bar;
>         bar = 1234;
>         {
>                 int fubar;
>                 for (fubar=0; fubar<bar; fubar++)
>                         printf("completely fooed\n");
>         }
> }
> 
> should compile. I believe that fubar is at least lexically visible to the
> end of the function, unlike some languages where the scope would be strictly
> the block.
Nope. Strictly the block.

HTH,
--ag
> 
> Comments from the language lawyers are welcome on what exactly the standard
> stipulates are welcome.

-- 
Artie Gold, Austin, TX  (finger the cs.utexas.edu account for more info)
mailto:agold@bga.com or mailto:agold@cs.utexas.edu
--
A: Look for a lawyer who speaks Aramaic...about trademark infringement.

Re: Declaring variables mid-function

[bowman]

Jamie Walker <jamie@sagaxis.co.uk> wrote:

>In standard C, you cannot declare variables part-way through any
>function.

I won't stick my neck out and say it is standard, as I don't have
Harbison & Steele handy, but gcc will accept declarations at the
head of any block. So

int foo() 
{
	int bar;
	bar = 1234;
	{
		int fubar;
		for (fubar=0; fubar<bar; fubar++)
			printf("completely fooed\n");
	}
}

should compile. I believe that fubar is at least lexically visible to the
end of the function, unlike some languages where the scope would be strictly
the block.

Comments from the language lawyers are welcome on what exactly the standard
stipulates are welcome.

Re: Declaring variables mid-function

[David Wragg]

Jamie Walker <jamie@sagaxis.co.uk> writes:
> In standard C, you cannot declare variables part-way through any
> function.

Yes you can. ISO C99 was passed a couple of months ago, and allows
mid-block declarations.

Of course, there are no compilers available yet that comprehensively
implement C99, and probably won't be for a couple of years (though
mid-block declarations will probably be one of the first C99 features
to appear). And people will be using C89 compilers for many years to
come, so you probably shouldn't expect to take advantage of C99
features for a while yet...

So get used to being specific about C89 or C99, rather than just
"standard C".


David Wragg

Re: Declaring variables mid-function

[Jamie Walker]

In article < jayaarzrhd.fsf@gatsby.u-net.com >, David Wragg
<dpw@doc.ic.ac.uk> writes
>Jamie Walker <jamie@sagaxis.co.uk> writes:
>> In standard C, you cannot declare variables part-way through any
>> function.
>
>Yes you can. ISO C99 was passed a couple of months ago, and allows
>mid-block declarations.
Thanks for that, David.
>
>Of course, there are no compilers available yet that comprehensively
>implement C99, and probably won't be for a couple of years (though
:o)
-- 
Jamie Walker                                  http://www.sagaxis.co.uk/
"lp1 reported invalid error status (on fire, eh?)", Linux error message
       PGP Key ID: 0x1B6BBB15 (available on public key servers)

Re: Declaring variables mid-function

[Jamie Walker]

In article < jayaarzrhd.fsf@gatsby.u-net.com >, David Wragg
<dpw@doc.ic.ac.uk> writes
>Jamie Walker <jamie@sagaxis.co.uk> writes:
>> In standard C, you cannot declare variables part-way through any
>> function.
>
>Yes you can. ISO C99 was passed a couple of months ago, and allows
>mid-block declarations.
Thanks for that, David.
>
>Of course, there are no compilers available yet that comprehensively
>implement C99, and probably won't be for a couple of years (though
:o)
-- 
Jamie Walker                                  http://www.sagaxis.co.uk/
"lp1 reported invalid error status (on fire, eh?)", Linux error message
       PGP Key ID: 0x1B6BBB15 (available on public key servers)

Re: Declaring variables mid-function

[David Wragg]

Jamie Walker <jamie@sagaxis.co.uk> writes:
> In standard C, you cannot declare variables part-way through any
> function.

Yes you can. ISO C99 was passed a couple of months ago, and allows
mid-block declarations.

Of course, there are no compilers available yet that comprehensively
implement C99, and probably won't be for a couple of years (though
mid-block declarations will probably be one of the first C99 features
to appear). And people will be using C89 compilers for many years to
come, so you probably shouldn't expect to take advantage of C99
features for a while yet...

So get used to being specific about C89 or C99, rather than just
"standard C".


David Wragg

Re: Declaring variables mid-function

[Jamie Walker]

In article < 385c11fa@oit.umass.edu >, Shawn <NRLax27@aol.com> writes
>    I am writing a medium sized program, and ran into a problem where gcc
>would not compile any function that did not have all of its variables
>declared as the first lines of the function.  As a test, I wrote this small
>program:
In standard C, you cannot declare variables part-way through any
function.

Move them to the top of the function and they will compile fine.

C++ does support what you want, so you could rename your .c files to .C
and gcc will treat them as C++, then they should work fine.

HTH,
-- 
Jamie Walker                                  http://www.sagaxis.co.uk/
"lp1 reported invalid error status (on fire, eh?)", Linux error message
       PGP Key ID: 0x1B6BBB15 (available on public key servers)

Re: Declaring variables mid-function

[Erik de Castro Lopo]

Shawn wrote:
> 
>     I am writing a medium sized program, and ran into a problem where gcc
> would not compile any function that did not have all of its variables
> declared as the first lines of the function. 

This is one of the differences between C and C++. C++ allows variables
to be declared anywhere a statement could be declared while C insists
all variables be declared at the start of a block.

So, you have two options:

1) Compile your program with g++ (the GNU C++ compiler) instead of gcc.

2) Change your code to legal C.

Erik
-- 
+-------------------------------------------------+
     Erik de Castro Lopo     erikd@zip.com.au
+-------------------------------------------------+
"Anyone who says you can have a lot of widely dispersed people hack
 away on a complicated piece of code and avoid total anarchy has never
 managed a software project." - Andy Tanenbaum in 1992 on comp.os.minix

Re: Declaring variables mid-function

[Erik de Castro Lopo]

Shawn wrote:
> 
>     I am writing a medium sized program, and ran into a problem where gcc
> would not compile any function that did not have all of its variables
> declared as the first lines of the function. 

This is one of the differences between C and C++. C++ allows variables
to be declared anywhere a statement could be declared while C insists
all variables be declared at the start of a block.

So, you have two options:

1) Compile your program with g++ (the GNU C++ compiler) instead of gcc.

2) Change your code to legal C.

Erik
-- 
+-------------------------------------------------+
     Erik de Castro Lopo     erikd@zip.com.au
+-------------------------------------------------+
"Anyone who says you can have a lot of widely dispersed people hack
 away on a complicated piece of code and avoid total anarchy has never
 managed a software project." - Andy Tanenbaum in 1992 on comp.os.minix

Declaring variables mid-function

[Shawn]

    I am writing a medium sized program, and ran into a problem where gcc
would not compile any function that did not have all of its variables
declared as the first lines of the function.  As a test, I wrote this small
program:

int test(char *tst, char *tst2, char **tst3);
int test2(void);

int main()
{
 test2();

 char *tst;
 char *tst2;
 char *tst3;

 test(tst, tst2, &tst3);

 return 1;

}

int test(char *tst, char *tst2, char **tst3)
{
 return 21;
}

int test2(void)
{
 return 21;
}

When trying to compile this, seemingly simple program, gcc complains.  This
is the output:

bash-2.03$ gcc test.c -o test
test.c: In function `main':
test.c:8: parse error before `char'
test.c:12: `tst' undeclared (first use in this function)
test.c:12: (Each undeclareed identifier is reported only once
test.c:12: for each function it appears in.)
test.c:12: `tst2' undeclared (first use in this function)
test.c:12: `tst3' undeclared (first use in this function)

Does anybody have any idea what is going on here?  My system is a Pentium,
with 48 MB ram, running Slackware Linux 7.0, gcc version 2.91.66 (egcs).
Thank you in advance!

-Shawn