[LLVMbugs] [Bug 20630] New: clang incorrectly infers that a fixed length array is a VLA when passing a const size through a function.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20630

            Bug ID: 20630
           Summary: clang incorrectly infers that a fixed length array is
                    a VLA when passing a const size through a function.
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ian.forbes at mail.mcgill.ca
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Clang allows C-style arrays of non-POD type but only when the size of these
array is known at compile time as per:
http://clang.llvm.org/compatibility.html#vla

However the following does not complile and complains that the array has a
variable length.

========================================

#include <vector>                                                               

void func(const int n)                                                          
{                                                                               
    std::vector<int> futs[n];                                                   
}                                                                               

int main()                                                                      
{                                                                               
    const int n = 5;                                                            
    func(n);                                                                    
}

========================================

works2.cpp:5:26: error: variable length array of non-POD element type
'std::vector<int>'
    std::vector<int> futs[n];
                         ^
1 error generated.

=========================================

This also happens when calling func with a literal.

The issue is that the size of the array is known at compile time but clang does
not know this unless the size is in the local scope of the function when the
array is being created.

This may not actually be a bug and may be the expected behaviour but if this is
the case the webpage should be updated to reflect this short comming. 

Additional Info:

Ubuntu clang version 3.5-1ubuntu1 (trunk) (based on LLVM 3.5)
Target: x86_64-pc-linux-gnu
Thread model: posix

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20140812/45258265/attachment.html>