Bug 87586 - C++ code compiles with mismatched angle brackets/parenthesis
Summary: C++ code compiles with mismatched angle brackets/parenthesis
Status: RESOLVED INVALID
Alias: None
Product: gcc
Classification: Unclassified
Component: c++ (show other bugs)
Version: 8.2.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2018-10-11 10:38 UTC by Gavin S
Modified: 2018-10-11 23:26 UTC (History)
1 user (show)

See Also:
Host:
Target:
Build:
Known to work:
Known to fail:
Last reconfirmed:


Attachments
Preprocessed File (90.04 KB, text/plain)
2018-10-11 10:38 UTC, Gavin S
Details

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Description Gavin S 2018-10-11 10:38:13 UTC
Created attachment 44827 [details]
Preprocessed File

I don't believe this code ought to compile due to the fact that there are mismatched angle brackets. Off the bat, I apologise if I have this wrong (due to things like digraphs):


    #include <iostream>
    
    template <typename TARGET, typename SOURCE>
    inline TARGET cast_integral_type(const SOURCE n)
    {
        // Simplified code here. Production code makes use of `#include <boost/numeric/conversion/cast.hpp>` here.
        return static_cast<TARGET>(n);
    }
    
    template <class TYPE>
    inline TYPE redundant_fn(TYPE x)
    {
        // Simplified code - was originally doing endian conversion
        return x;
    }

    int main(int argc, char *argv[])
    {
        const int nRedundantVar = 0;
        
    #if 0 // Tried to simplify - does not compile.
        std::cout << cast_integral_type<uint16_t, int>(nRedundantVar)>(0x64) << std::endl; // Rect width
        std::cout << cast_integral_type<uint16_t, int>(nRedundantVar)>(0x64) << std::endl; // Rect height
    #endif
        
        // BAD: Unexpectedly print "0".
        std::cout << redundant_fn<uint16_t>(cast_integral_type<uint16_t, int>(nRedundantVar)>(0x64)) << std::endl;
        
        // BAD: Remove iostreams - Unexpectedly print "0".
        int x = (redundant_fn<uint16_t>(cast_integral_type<uint16_t, int>(nRedundantVar)>(0x64)));
        std::cout << x << std::endl;

        // OK
        int y = redundant_fn<uint16_t>(cast_integral_type<uint16_t, int>(0x64));
        std::cout << y << std::endl;
        
        return 0;
    }  

Preprocessed file attached. Reproducible in both 7.3.0 and 8.2.0 (using packages made available via Ubuntu 18.04 package manager).

g++ -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 8.2.0-1ubuntu2~18.04' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 8.2.0 (Ubuntu 8.2.0-1ubuntu2~18.04) 

Code sample built using:
    g++ main.cpp -o test
Comment 1 Harald van Dijk 2018-10-11 19:21:54 UTC
> without a matching < is taken simply as the greater-than operator. You are checking whether cast_integral_type<uint16_t, int>(nRedundantVar) is greater than (0x64), which is valid so should compile successfully, even if it is not what you intended.
Comment 2 Gavin S 2018-10-11 21:43:47 UTC
Bah - I feel stupid. So obvious once you pointed it out. Consider this closed.
Comment 3 Jonathan Wakely 2018-10-11 23:26:00 UTC
Closing.