了解在共享库中重载operator new的行为

Question

我正在使用Centos平台上的共享库和应用程序[clang ++,llvm3.9.0和libc ++],并且库和应用程序都会重载它们自己的operator new和operator delete.

除1例外,一切正常.在调用std :: string的copy构造函数时总是调用应用程序端的operator new:

这是senario:

std::string str1 ( "A very strange issue on CentOS using clang and libc++" ); //operator new of library side called.

std::string str2(str1); //operator new of application side called. WHY??

对于库侧调用两种情况下的operator delete.

以下是运行以下代码时的日志:

====================================================
operator new in shared library
operator new called Application side
operator delete in shared library
operator delete in shared library
====================================================

共享库侧操作员new和delete:

    void * operator new ( size_t len ) throw ( std::bad_alloc )
    {
        printf("operator new in shared library\n");
        void * mem = malloc( len );
        if ( (mem == 0) && (len != 0) ) throw std::bad_alloc();
        return mem;
    }

    void * operator new[] ( size_t len ) throw ( std::bad_alloc )
    {
        printf("operator new[] in shared library\n");
        void * mem = malloc( len );
        if ( (mem == 0) && (len != 0) ) throw std::bad_alloc();
        return mem;
    }

    void operator delete ( void * ptr ) throw()
    {
        printf("operator delete in shared library\n");
        if ( ptr != 0 ) free ( ptr );
    }

    void operator delete[] ( void * ptr ) throw()
    {
        printf("operator delete[] in shared library\n");
        if ( ptr != 0 ) free ( ptr );
    }

应用程序端操作员new和operator delete:

void * operator new ( size_t len ) throw ( std::bad_alloc )
{
    void * mem = malloc ( len );
    printf("operator new called Application side\n");
    if ( (mem == 0) && (len != 0) ) throw std::bad_alloc();
        return mem;
}

void * operator new[] ( size_t len ) throw ( std::bad_alloc )
{
    void * mem = malloc ( len );
    printf("operator new[] called Application side\n");
    if ( (mem == 0) && (len != 0) ) throw std::bad_alloc();
        return mem;
}

void operator delete ( void * ptr ) throw()
{
    printf("operator delete[] called Application side\n");
    if ( ptr != 0 )free ( ptr );
}

void operator delete[] ( void * ptr ) throw()
{
    printf("operator delete[] called Application side\n");
    if ( ptr != 0 ) free ( ptr );
}

请帮忙.

Answer 1

简短的回答:不要这样做.

还有的只应该是一个替换operator new(OK,还有一堆的味道,喜欢noexcept,和[]等,但只有每一个味道).

如果您有多个,那么 - 正如您所发现的那样 - 不清楚哪个被调用,并且您可以获得对new和delete的不匹配调用,这是对未定义行为的快速访问.

我可以解释为什么你得到了你正在报告的确切行为,但它与内联模板和外部模板有关,而且它并不重要.你有两个替换功能operator new,这就是问题所在.