no matching constructor for initialization of '

问题:

This question already has an answer here:

• Is initializer list like this legal in C++11? 1 answer

I'm learning c++ with C++ Primer, 5th ed..

I'm trying to compile a simple c++ program with C++11 features with clang++ but I'm getting compile errors for what should be valid code.

This is an example:

#include <iostream>
#include <vector>
#include <string>

using namespace std;

int main(){
  int n = 0;
  auto *p = &n; //<-- this compiles  

  cout << *p << endl;

  vector<string> articles = {"a", "an", "the"}; //<-- this fails; copied from the book

  return 0;
}

And this is the complete error:

$ clang++ -std=c++11 -v test.cpp -o test
clang version 3.2 (tags/RELEASE_32/final)
Target: x86_64-apple-darwin10.8.0
Thread model: posix
 "/usr/local/Cellar/llvm/3.2/bin/clang" -cc1 -triple x86_64-apple-macosx10.6.0 -emit-obj -mrelax-all -disable-free -main-file-name test.cpp -mrelocation-model pic -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 127.2 -v -resource-dir /usr/local/Cellar/llvm/3.2/bin/../lib/clang/3.2 -fmodule-cache-path /var/folders/pk/pkIeYbRaF-yeeUH3Q6Q5AE+++TI/-Tmp-/clang-module-cache -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Users/Oton/Desktop -ferror-limit 19 -fmessage-length 150 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.6.0 -fobjc-dispatch-method=mixed -fobjc-default-synthesize-properties -fencode-extended-block-signature -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/pk/pkIeYbRaF-yeeUH3Q6Q5AE+++TI/-Tmp-/test-w65CaF.o -x c++ test.cpp
clang -cc1 version 3.2 based upon LLVM 3.2svn default target x86_64-apple-darwin10.8.0
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/4.2.1
 /usr/include/c++/4.2.1/i686-apple-darwin10/x86_64
 /usr/include/c++/4.2.1/backward
 /usr/include/c++/4.0.0
 /usr/include/c++/4.0.0/i686-apple-darwin8
 /usr/include/c++/4.0.0/backward
 /usr/local/include
 /usr/local/Cellar/llvm/3.2/bin/../lib/clang/3.2/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
test.cpp:13:18: error: no matching constructor for initialization of 'vector<string>'
  vector<string> articles = {"a", "an", "the"};
                 ^          ~~~~~~~~~~~~~~~~~~
/usr/include/c++/4.2.1/bits/stl_vector.h:255:9: note: candidate constructor [with _InputIterator = const char *] not viable: no known conversion from
      'const char [4]' to 'const allocator_type' (aka 'const std::allocator<std::basic_string<char> >') for 3rd argument
        vector(_InputIterator __first, _InputIterator __last,
        ^
/usr/include/c++/4.2.1/bits/stl_vector.h:213:7: note: candidate constructor not viable: no known conversion from 'const char [2]' to 'size_type'
      (aka 'unsigned long') for 1st argument
      vector(size_type __n, const value_type& __value = value_type(),
      ^
/usr/include/c++/4.2.1/bits/stl_vector.h:201:7: note: candidate constructor not viable: allows at most single argument '__a', but 3 arguments were
      provided
      vector(const allocator_type& __a = allocator_type())
      ^
/usr/include/c++/4.2.1/bits/stl_vector.h:231:7: note: candidate constructor not viable: requires single argument '__x', but 3 arguments were provided
      vector(const vector& __x)
      ^
1 error generated.

I'm on a mac, 10.6.8, I built llvm/clang with homebrew with options:

brew install llvm -v --all-targets --rtti --shared --with-asan --with-clang --use-clang

What am I doing wrong?

回答1:

The error tells you that there's no std::vector constructor taking an initializer list. The problem is that the standard library implementation you are using has not been updated for C++11. You are using the gcc 4.2 version of libstdc++, which was written years before C++11.

You have to switch to a library that has been updated for C++11. If you have libc++ installed then you can do just use the flag -stdlib=libc++. I think the libc++ binary is a part of OS X 10.6.8, but you'll also need headers. Maybe homebrew has a recipe, or you can just download them from: http://libcxx.llvm.org/ and stick them in the appropriate location to be found found and used with -stdlib=libc++.

Alternatively you can manually leave out the normal C++ standard library headers (the gcc 4.2 ones in this case) with -nostdinc++, manually add an include directory for wherever you stick the headers, add a library search directory for wherever the binary is (you can even build the binary yourself) and add the link flag -lc++.

回答2:

I'm not sure if this is good norm but I'll answer my own question. I hope this will help others.

(I am just a beginner so if I'm doing something wrong please correct me.)

The only way to build the example above is with:

-std=c++11 -stdlib=libc++ -nostdinc++ -I/path/to/new/libcxx/include

The problem is Snow Leopard which, as others have said here, has a very old version of gcc. And using the options above fails to link because of ld: library not found for -lc++.

So I had to build a recent version of libcxx. There is a macports port but no recipe for homebrew. I built it manually but there are some things I had to go around to succede.

I assume you have installed llvm with homebrew and your path is set up properly: which clang++ -> /usr/local/bin/clang++.

First get libc++abi: svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi

then get libc++: svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx.

Edit libc++abi/lib/buildit:

EXTRA_FLAGS="...
             -I/usr/llvm-gcc-4.2/lib/gcc/i686-apple-darwin10/4.2.1/include \
             -I/PATH/TO/libcxx/include"
(Add the last two lines, note that the last include should point to the include folder inside libcxx from svn.)

LDSHARED_FLAGS="...-install_name /usr/local/lib/libc++abi.dylib"
(My libc++abi.dylib will reside inside /usr/local/lib.)

Now build libc++abi:

- cd libc++abi/lib 
- export TRIPLE=-apple-
- ./buildit

I prefer to manage all my 3rd party libraries with homebrew, so this is optional:

- mkdir -p /usr/local/Cellar/libc++abi/HEAD/lib
- mkdir -p /usr/local/Cellar/libc++abi/HEAD/include
- cp -a *.dylib /usr/local/Cellar/libc++abi/HEAD/lib/
- cp -R /path/to/libcxxabi/include/ /usr/local/Cellar/libc++abi/HEAD/include/libc++abi
  (Note the / after include!)
- brew link libc++abi

Now edit libc++/lib/buildit:

if [ "$MACOSX_DEPLOYMENT_TARGET" == "10.6" ]
then
    EXTRA_FLAGS="... -I/usr/local/include/libc++abi"
    LDSHARED_FLAGS="...
        -install_name /usr/local/lib/libc++.1.dylib \
        ..."

Now build libc++:

- cd libc++abi/lib 
- export TRIPLE=-apple-
- export MACOSX_DEPLOYMENT_TARGET=10.6
- ./buildit

And again optional:

- mkdir -p /usr/local/Cellar/libc++/HEAD/lib
- cp -a *.dylib /usr/local/Cellar/libc++/HEAD/lib
- mkdir -p /usr/local/Cellar/libc++/HEAD/include
- cp -R /path/to/libcxx/include/ /usr/local/Cellar/libc++/HEAD/include/libc++
- brew link libc++

I can now build the previous example with:

clang++ -std=c++11 -stdlib=libc++ -nostdinc++ -I/usr/local/include/libc++ -O2 -g -v test.cpp -o test