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我使用 travis 测试我的代码。最近有人将 gcc9 添加到测试代码的编译器集中。虽然使用 gcc8（使用 c++14 和 c++17）和使用 c++14 的 gcc-9.1.0 都可以正常编译，但使用 c++17 的 gcc-9.1.0 会失败，并出现以下错误：

/usr/include/c++/9/functional: In instantiation of ‘std::_Bind<_Functor(_Bound_args ...)>::_Bind(const _Functor&, _Args&& ...) [with _Args = {std::tuple<int>}; _Functor = SQLite::Statement; _Bound_args = {std::tuple<int>}]’:
/usr/include/c++/9/functional:811:38:   required from ‘typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type std::bind(_Func&&, _BoundArgs&& ...) [with _Func = SQLite::Statement&; _BoundArgs = {std::tuple<int>}; typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type = std::_Bind<SQLite::Statement(std::tuple<int>)>]’
/home/travis/build/SRombauts/SQLiteCpp/include/SQLiteCpp/ExecuteMany.h:84:9:   required from ‘void SQLite::bind_exec(SQLite::Statement&, std::tuple<_Tps ...>&&) [with Types = {int}]’
/home/travis/build/SRombauts/SQLiteCpp/include/SQLiteCpp/ExecuteMany.h:50:14:   required from ‘void SQLite::execute_many(SQLite::Database&, const char*, Arg&&, Types&& ...) [with Arg = std::tuple<int>; Types = {std::tuple<int, const char*>, std::tuple<int, const char*>}]’
/home/travis/build/SRombauts/SQLiteCpp/tests/ExecuteMany_test.cpp:35:9:   required from here
/usr/include/c++/9/functional:462:59: error: ‘SQLite::Statement::Statement(const SQLite::Statement&)’ is private within this context
  462 |  : _M_f(__f), _M_bound_args(std::forward<_Args>(__args)...)
      |                                                           ^
In file included from /home/travis/build/SRombauts/SQLiteCpp/include/SQLiteCpp/Column.h:13,
                 from /home/travis/build/SRombauts/SQLiteCpp/include/SQLiteCpp/Database.h:13,
                 from /home/travis/build/SRombauts/SQLiteCpp/tests/ExecuteMany_test.cpp:13:
/home/travis/build/SRombauts/SQLiteCpp/include/SQLiteCpp/Statement.h:696:5: note: declared private here
  696 |     Statement(const Statement&);

引发此错误的代码如下：

template <typename Arg, typename... Types>
void execute_many(Database& aDatabase, const char* apQuery, Arg&& aArg, Types&&... aParams)
{
    Statement query(aDatabase, apQuery);
    bind_exec(query, std::forward<Arg>(aArg));
    (void)std::initializer_list<int>
    {
        ((void)reset_bind_exec(query, std::forward<Types>(aParams)), 0)...
    };
}

template <typename TupleT>
void reset_bind_exec(Statement& apQuery, TupleT&& aTuple)
{
    apQuery.reset();
    bind_exec(apQuery, std::forward<TupleT>(aTuple));
}

template <typename TupleT>
void bind_exec(Statement& apQuery, TupleT&& aTuple)
{
    bind(apQuery, std::forward<TupleT>(aTuple));
    while (apQuery.executeStep()) {}
}

我使用下面的代码让travis CI使用对应的编译器

matrix:
  include:
    - compiler: gcc
      addons:
        apt:
          sources:
            - ubuntu-toolchain-r-test
          packages:
            - g++-9
      env:
        - CC=gcc-9
        - CXX=g++-9
        - CXXFLAGS="-std=c++17 -Wall -Wextra -pedantic"

before_install:
  # coveralls test coverage:
  - if [[ "$CXX" == "g++" ]]; then pip install --user cpp-coveralls ; fi

# scripts to run before build
before_script:
  - gcc --version
  - mkdir build
  - cd build
  - cmake -DCMAKE_BUILD_TYPE=Debug -DSQLITECPP_USE_GCOV=ON -DSQLITECPP_BUILD_EXAMPLES=ON -DSQLITECPP_BUILD_TESTS=ON ..

# build examples, and run tests (ie make & make test)
script:
  - cmake --build .
  - ctest --verbose --output-on-failure

类 Statement 有一个私有复制构造函数和赋值运算符，但我想知道为什么这会在这里引起任何问题，因为我没有复制 Statement“查询”。尤其是为什么这个问题只发生在带有 c++17 的 gcc-9.1.0 上（在我的本地机器上，我使用 gcc-9.1.1 并且编译时没有任何错误）。

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1 回答 1

1

一个更简单的例子是：

#include <functional>

namespace SQLite
{
    struct Statement
    {
        Statement() = default;
        Statement(const Statement&) = delete;
    };
    template<class ...Args>
    void bind( Statement& s, const Args& ... args )
    {        
    }

    template < typename T >
    void test(T&& t)
    {
        Statement s;
        bind( s, std::forward< T >( t ) );
    }    
}

int main() 
{
    std::tuple< int > t;
    SQLite::test( t );
}

由于您的参数之一来自std命名空间 Argument Dependent Lookup ，因此将std::bind其带入了可用函数列表。在调用之前SQLite::bind需要转换为，所以是更好的匹配。const&std::bind

您有几个选项可以解决此问题：

  1. 显式调用SQLite::bind
  2. 将名称更改bind为不在标准库中的名称（这可能是最好的选择，因为它可以阻止您的用户遇到相同的问题）
  3. changebind的参数从const Args& ... argstoArgs&& ... args删除转换
于 2019-06-26T08:51:42.873 回答