[cfe-users] Part/complete compilation with clang++

Sian Mountbatten poenikatu at fastmail.co.uk
Sat Jul 20 09:30:24 PDT 2013

On 2013-07-20 17:25, David Blaikie wrote:
> On Sat, Jul 20, 2013 at 6:46 AM, Sian Mountbatten
> <poenikatu at fastmail.co.uk> wrote:
>> Dear List
>> I have a small program which contains the code shown on page 1058 of
>> Stroustrup's TC++PL (4th ed.) just above the 37.2.1 section. I omitted
>> the line which initialises (and declares) pat1.
> Not everyone has a copy of TC++PL on hand, perhaps you could provide
> the code you are compiling?
>> If I compile the file main.cpp to regex using this command:
>>     clang++ -g -std=c++11 -stdlib=libc++ -o regex main.cpp
>> I get no warnings, no errors, in fact no console output from clang++.
>> When the program is run, it produces "\w+\d*" on the console.
> If you avoid initializing a variable you may get undefined behavior,
> which isn't going to be reliable.
>> Now, if I compile with this command:
>>    clang++ -g -std=c++11 -o main.o -c main.cpp
>> and then link with this command:
>>    clang++ -g -stdlib=libc++ -o regex main.o
>> again, I get no output from clang++. Unfortunately, when the output
>> program is run, it fails with "Segmentation violation".
> Again, I'm assuming you've invoked UB & the two different standard
> libraries are just failing in different ways. Once we see the code,
> that might change.
>> Does this mean that when I start writing programs which are made up
>> of many source files, I shall be unable to compile the individual files?
> I don't understand this question, well maybe - no, there shouldn't
> really be any difference between compiling and then linking and
> compiling+linking in one go. But UB is UB (though I'd still be
> surprised if that actually behaves differently)
>> I am trying to use Code::Blocks as the IDE for clang++. The commands it
>> issues are peculiar and, especially, the linker is, I reckon, just plain
>> wrong. The point is that the Code::Blocks binary also fails with a
>> Segmentation violation.
>> So what's going wrong? Can clang++ act, not only as a compiler, but also a
>> linker?
> Both GCC and Clang (& many other compilers) can act as wrappers around
> assemblers and linkers. They just invoke the assembler (well,
> Clang/LLVM has an integrated assembler too, so it doesn't invoke
> another process to assemble) or linker with the relevant arguments
> (such as figuring out the right libraries to link for the standard
> library, etc)
>> And is it possible to use a debugger from the LLVM stable rather
>> than
>> GNU gdb?
> There is a debugger under the LLVM project, called LLDB - it's not
> very mature & even less so on Linux. Clang's debug info should operate
> perfectly well with GDB, if it doesn't, please file bugs.
>> Looking forward to progessing on these points.
>> --
>> Sian Mountbatten <www.poenikatu.co.uk>
>> Learning C++!!!
>> I'm an FSF member (no. 10888)
>> Help us support software freedom! http://www.fsf.org/jf?referrer=10888
>> _______________________________________________
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Sian Mountbatten
Learning C++!!!
I'm an FSF member
Help us support software freedom! http://www.fsf.org/jf?referrer=10888

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