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How to make gcc warn about arithmetic signed overflow?

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How to make gcc warn about arithmetic signed overflow?
posted Sep 21, 2013 by Bob Wise

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1 Answer

+1 vote

If ab and bc are 'const' then G++ will warn:

o.cc: In function ‘int main()’:
o.cc:5:14: warning: integer overflow in expression [-Woverflow]
 int r = ab * bc;
 ^

The C compiler still doesn't warn though, due to different rules for how constants are handled between C and C++.

answer Sep 21, 2013 by Sumit Pokharna
Yes, gcc the Gnu Compiler Collection can produce such a warning:

procedure test_ovf is
 ab : integer := 50000;
 bc : integer := 50000;
 r : integer := ab * bc;
begin
 null;
end test_ovf;

gcc -c test_ovf.adb
test_ovf.adb:4:22: warning: value not in range of type "Standard.Integer"
test_ovf.adb:4:22: warning: "Constraint_Error" will be raised at run time
However I'm not sure it is allowed to do the same with C.
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0 votes

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+1 vote

I don't really understand this option. I enabled it but it warns for essentially all of my classes which have any virtual methods. For
example if I have Foo.h:

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then Foo.cpp which implements Foo. And then in another header somewhere else I inherit from Foo and implement bar() differently (as a virtual function). However when GCC compiles Foo.cpp it can't see the other header, so I guess it assumes no one inherits from Foo and suggests it should be marked final:

Declaring type 'class Foo' final would enable devirtualization of N calls

I mean sure, it would, but that would defeat the entire point (as I understand it).

I don't really understand how/where this option is meant to be used.
Ditto for -Wsuggest-final-methods.

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