Gotos past local variable initialization

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2 total messages Started by Mike Bolotski Sun, 19 Nov 1989 05:22

#599

Author: Mike Bolotski
Date: Sun, 19 Nov 1989 05:22

39 lines
1822 bytes

I'm not sure if this is a g++ bug or a V2.0 feature. In any case,
similar code worked fine under 1.35.   The compiler complains about
the jump past the initialization point.  In this example, the goto
can be replaced by a continue; in the actual application, the goto 
is used as a continue(3) equivalent (continue with loop 3 levels out),
so no flames about goto's. Please.

-----

Script started on Sat Nov 18 21:16:31 1989
coho{mikeb}101: g++ -v lambda.cc
gcc version 1.36.1 (based on GCC 1.36)
 /usr/local/lib/gnu/gcc-cpp -+ -v -undef -D__GNUC__ -D__GNUG__ -D__cplusplus -Dmc68000 -Dsun -Dunix -D__mc68000__ -D__sun__ -D__unix__ -D__HAVE_68881__ -Dmc68020 lambda.cc /usr/tmp/cca09073.cpp
GNU CPP version 1.36
 /usr/local/lib/gnu/gcc-cc1plus /usr/tmp/cca09073.cpp -quiet -dumpbase lambda.cc -version -o /usr/tmp/cca09073.s
GNU C++ version 1.36.1 (based on GCC 1.36) (68k, MIT syntax) compiled by GNU C version 1.36.
default target switches: -m68020 -mc68020 -m68881 -mbitfield
lambda.cc: In function int main ():
lambda.cc:14: invalid jump to label `nextp'
lambda.cc:11: crosses initialization of `q'
coho{mikeb}102: cat lambda.cc

#include <stdio.h>

int main()
{
 
   for (int p = 100; p ; ) {            
      if (p > 10)
           goto nextp; 
   
       short q = 7 * p; 
       if (q > 4)
          printf("Hello\n");
nextp: ;
   }
}
coho{mikeb}103: exit
exit

Gotos past local variable initialization

#600

Author: Michael Tiemann
Date: Sun, 19 Nov 1989 05:29

49 lines
1794 bytes

   Date: 18 Nov 89 21:22 -0800
   From: Mike Bolotski <mikeb@ee.ubc.ca>

   I'm not sure if this is a g++ bug or a V2.0 feature. In any case,
   similar code worked fine under 1.35.   The compiler complains about
   the jump past the initialization point.  In this example, the goto
   can be replaced by a continue; in the actual application, the goto 
   is used as a continue(3) equivalent (continue with loop 3 levels out),
   so no flames about goto's. Please.

   -----

   coho{mikeb}101: g++ -v lambda.cc
   [...]
   lambda.cc: In function int main ():
   lambda.cc:14: invalid jump to label `nextp'
   lambda.cc:11: crosses initialization of `q'
   coho{mikeb}102: cat lambda.cc

   #include <stdio.h>

   int main()
   {

      for (int p = 100; p ; ) {            
	 if (p > 10)
	      goto nextp; 

	  short q = 7 * p; 
	  if (q > 4)
	     printf("Hello\n");
   nextp: ;
      }
   }
   coho{mikeb}103: exit
   exit

It's a 2.0 feature.  cfront 2.0 also gives an error:

cfront < l5.cc > /dev/null
"", line 9: error: goto nextp past initialized q
teacake% 

Both compilers will let you use continue.  If you want a work-around,
just wrap `q' in a scope which makes it invisible at `nextp'.

Michael

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