CODEWITHSUNDEEP
c++pthreads
Mostafa Talebi
Mostafa Talebi

Reputation: 9183

Casting int to void* loses precision, and what is the solution in required cases

I know the reason of such error. "int" is not large enough to hold bytes of "void *". But my question is that how should I then handle pthread_create of Linux, when I want to pass a function's argument for it to be executed. In many examples, I see such function forward-declaration:

void* thread_proc(void* arg);

And then in the function, a file-pointer is passed as arg (which is of type int). But the compiler (logically) throws an error which warns against the casting of int to void. I even have used the intptr_t (aka long pointer) but to no avail.

result = pthread_create(&thread_id, NULL, thread_proc, (void *)new_request_socket);

new_request_socket is an int representing the fd of a socket.

How the I can pass an integer as an argument of a function is itself passed as function to be executed by pthread_create().

Upvotes: 0

Views: 311

Answers (1)

NP Rooski Z
NP Rooski Z

Reputation: 3677

You are probably passing int itself not pointer to the int.

You should actually pass pointer

result = pthread_create(&thread_id, NULL, thread_proc, (void *)&new_request_socket);

And in thread_proc(void *arg) use it as such:

void thread_proc(void *arg)
{
    int  new_request_socket = *arg; //please put appropriate cast
}

EDIT: To clarify what Sam and Lightness points about passing the pointer thread_proc:

  • Dont pass pointer to the local variable i.e. new_request_socket should be allocated on heap using malloc
  • simultaneous access to new_request_socket should be streamlined using locks
  • Dont free new_request_socket until thread_proc reads it.

Essentially making new_request_socket a pointer you will have to write more code. So dont write more code and use std::thread :)

Upvotes: 1

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