Lambda Expression Equivalent C++ Code

Question

I downgraded gcc compiler for 4.9.2 to 4.4.1, as I know 4.4.1 doesn't support lambda expressions. In the following code, a lambda expression [](void*d){ dlclose(d); } is used and facing error due to lambda expression. Can anyone help how to use below code without lambda expression?

using libs_t = std::unique_ptr<void,std::function<void(void*)>>;

I replaced the above line with the below but it's also not supported by gcc 4.4.1

typedef std::unique_ptr<void,std::function<void(void*)>> libs_t ;

m_libs[ lib_name ] = libs_t ( handle, [](void*d){ dlclose(d); } );

@user3906620 Just define a function with such a body as the lambda expression — Vlad from Moscow
– Vlad from Moscow, Commented Nov 2, 2017 at 12:23
Can you provide the declaration of dlclose? Why is the lambda even needed? — MSalters
– MSalters, Commented Nov 2, 2017 at 12:39

user7860670 · Accepted Answer · 2017-11-02 12:44:02Z

3

You can redefine unique_ptr specialization to accept raw function pointer instead of std::function:

typedef std::unique_ptr<void, int ( * )(void *)> libs_t ;
libs_t(handle, &dlclose);

Use of std::function in this case seems to be redundant because the only item that is supposed to be stored in it is a pointer to dlclose function.

edited Nov 2, 2017 at 12:44

answered Nov 2, 2017 at 12:32

user7860670

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2 Comments

Iqbal Haider Over a year ago

After above changes, error is static assertion failed: "constructed with null function pointer deleter"

user7860670 Over a year ago

@user3906620 This means that you are creating libs_t instances using default constructor. This is prohibited when deleter is a pointer to function. To fix this create libs_t instances supplying nullptr and a pointer to dlclose as parameters.

Baum mit Augen · Accepted Answer · 2017-11-02 12:28:50Z

1

Just try dlclose.

No, really. It may run into problems with void return values, but if that happens write

void mydlclose(void* p){ dlclose(p); }

and use mydlclose.

edited Nov 2, 2017 at 12:28

Baum mit Augen♦

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answered Nov 2, 2017 at 12:25

Yakk - Adam Nevraumont

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