c++ - 内部移动 std::vector 元素和 QVector

Question

有两个 vector std::vector 和 QVector。我们必须检查插入时如何“移动”元素。 (用五个元素构造两个 vector 并插入零元素)我有这段代码:

#include <QVector>
#include <QTextStream>

struct MoveTest
{
    int i;

    MoveTest()                       {}
    MoveTest(const MoveTest& other)  {QTextStream(stdout) << "constr copy" << endl;}
    MoveTest(MoveTest &&other)       {QTextStream(stdout) << "constr move" << endl;}
    ~MoveTest()                      {}

    inline MoveTest&    operator=   (const MoveTest& other) {QTextStream(stdout) << "copy" << endl;}
    inline MoveTest&    operator=   (MoveTest &&other)      {QTextStream(stdout) << "move" << endl;}
};

int main(int argc, char *argv[])
{
    QTextStream(stdout) << "std::move:" << endl;
    MoveTest t1;
    MoveTest t2(std::move(t1));
    t1 = std::move(t2);

    QTextStream(stdout) << "QVector:" << endl;
    QVector<MoveTest> qmTest(5);
    qmTest.insert(qmTest.begin(), MoveTest());

    QTextStream(stdout) << "std::vector:" << endl;
    std::vector<MoveTest> mTest(5);
    mTest.insert(mTest.begin(), MoveTest());

    return 0;
}

我使用 gcc 4.7.2 的输出，QMAKE_CXXFLAGS += -std=c++0x:

std::move:
constr move
move
QVector:
constr copy
constr copy
constr copy
constr copy
constr copy
constr copy
copy
copy
copy
copy
copy
copy
std::vector:
constr move
constr copy
constr copy
constr copy
constr copy
constr copy

如何在不复制的情况下插入具有内部移位的元素？需要哪些 GCcflags？

Answer 1

由于您的移动操作符可以抛出异常，std::vector 不能使用它。如果运算符(operator)在调整大小过程中途抛出异常，它会怎么做？声明它noexcept如果它不能抛出异常并且 vector 实现可以使用它。