CODEWITHSUNDEEP
c++multithreadingvisual-c++c++11visual-studio-2012
code muncher
code muncher

Reputation: 1682

Constructing a std::thread with a function

This works:

    std::thread t = std::thread(printf, "%d", 1);

This doesn't work:

t2 = std::thread(my_thread_func , std::ref(context));

OR

std::thread t1 = std::thread(my_thread_func , context_add);

my_thread_func definition : 

int my_thread_func(long long *context_add)

context is some struct .. and I'm trying to do 'pass by reference'

Error:

function call missing argument list;

error C2661: 'std::thread::thread' : no overloaded function takes 2 arguments

>>> EDIT <<<

Sorry for confusion ... actually I'm defining my_thread_func in public of MainPage, so I cannot use native type hence I thought worth trying for long and give it address.

/* test data types, context for thread function, in .cpp (not in namespace) */
typedef struct _test_context
{
    HANDLE hHandle;
    unsigned int flag;
}test_context_t;

test_context_t *context;
//Do something with its member
context_add = (long long *)context;
std::thread t2 = std::thread(sem_waiting_thread, context_add);

ERROR:

error C3867: 'App1::MainPage::my_thread_func': function call missing argument list; use '&App1::MainPage::my_thread_func' to create a pointer to member
error C2661: 'std::thread::thread' : no overloaded function takes 2 arguments

my namespace looks like:

namespace App1
{
    public ref class MainPage sealed
    {
   public:
    MainPage();
       public:
           MainPage();
           int my_thread_func(long long cotext);
      ..
    };
}

<<<< EDIT 2 >>> I'm curious now .. this simple one also doesn't work!

void f1(int n)
{
    for(int i=0; i<5; ++i) {
        // Print n
        std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }
} 
.
.
.

int n=0;
std::thread t2(f1, n+1); (//This didn't work,same error!)

.
.
.
but this worked!
std::thread t2;
.
.
.
t2= std::thread (f1, n+1);

Trying from here: http://en.cppreference.com/w/cpp/thread/thread/thread

Upvotes: 1

Views: 4498

Answers (1)

betabandido
betabandido

Reputation: 19704

It would be better to define your function as:

int my_thread_func(context& ctx);

Then you would be able to pass a reference to a context. If the function is not supposed to modify the context then it is better to use:

int my_thread_func(const context& ctx);

Then you can create the thread like:

test_context_t context;
/* ... */
std::thread t = std::thread(my_thread_func , std::ref(context));

From your code it seems you have a pointer to a context. You might want to reconsider that and just use an object instance as I do above. If the context is passed to a function as a pointer you might want to change that pointer to a reference too. But if that is not possible (or desirable) then you can still create the thread by doing:

test_context_t* context;
/* ... */
std::thread t = std::thread(my_thread_func , std::ref(*context));

Alternatively, you can just use plain pointers:

int my_thread_func(context* ctx); // notice the different function's signature

test_context_t* context;
/* ... */
std::thread t = std::thread(my_thread_func , context);

Upvotes: 5

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