Reading input in using pthreads

Question

I am trying to read in input from the command line using a pthread. The pthread would call a reading function. Having some trouble with this and I have read the POSIX documentation. Appreciate the help!

int main(int argc , char *argv[])
{
    pthread_t client_thread; // client thread
    int rc;
    string msg;
    cout<<"Please enter a message to send to the server: "<<endl;
    pthread_create(&client_thread, NULL, readerT, &msg);

    cout<<"Msg is: "<<msg<<endl;

    return 0;
}

void * readerT(string * temp)
{
    cout<<"GOT IN HERE:\n"<<endl;
    getline(cin,*temp);
}

Current Error Msg:

Client.cpp: In function ‘int main(int, char**)’:
Client.cpp:33: error: invalid conversion from ‘void* (*)(std::string*)’ to ‘void* (*)(void*)’
Client.cpp:33: error:   initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’

join the created thread, so that the main thread will not come to an end. — Whoami
– Whoami, Commented Mar 3, 2014 at 5:15
i added the pthread_join(client_thread, NULL); after the cout<<"Msg is... but I get a bunch of errors with regards to invalid conversions :( — Masterminder
– Masterminder, Commented Mar 3, 2014 at 5:25
1) Check return value of thread creation, make sure you edit the question with proper error message so that, engineers can help you with ease. — Whoami
– Whoami, Commented Mar 3, 2014 at 5:31
If your compiler supports c++11 you might consider using std::thread, see this example nullptr.me/2011/09/16/multithreading-in-c11-part-1/… — amdn
– amdn, Commented Mar 3, 2014 at 5:44
@Masterminder I have made few changes in my answer it should work now... check... — HadeS
– HadeS, Commented Mar 3, 2014 at 9:11

alk · Accepted Answer · 2014-03-03 07:19:10Z

3

Just read the error message:

Client.cpp:33: error: invalid conversion from ‘void* (*)(std::string*)’ to ‘void* (*)(void*)’

The thread function has to be of type:

void * (*)(void *)

To change this

void * readerT(string * temp)

to be

void * readerT(void * temp)

answered Mar 3, 2014 at 7:19

alk

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Comments

HadeS · Accepted Answer · 2014-03-03 15:28:40Z

1

#include<iostream>
#include <pthread.h>
using namespace std;

void * readerT(void* );
int main(int argc , char *argv[])
{
    pthread_t client_thread; // client thread
    int rc;
    string msg;
    cout<<"Please enter a message to send to the server: "<<endl;
    pthread_create(&client_thread, NULL, readerT, &msg);
    pthread_join(client_thread,NULL);
    cout<<"Msg is: "<<msg<<endl;

    return 0;
}

void * readerT(void * temp)
{
    string *tmp = (string*)(temp);
    getline(cin,*tmp);
}

Hope that will work...(try to analyze what was wrong with your code :-) )

edited Mar 3, 2014 at 15:28

answered Mar 3, 2014 at 5:33

HadeS

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7 Comments

alk Over a year ago

Although you are roughly pointing to a bug, it still is not related to question at all. Moreoever, an answer should explain what is wrong and how it can be fixed (if ever).

HadeS Over a year ago

I guess you haven't saw the original question... error was obvious and yes I havn't worked with pthread so was not aware of the syntax..

HadeS Over a year ago

I think you should visit this before saying that .....cplusplus.com/reference/string/string/getline

Masterminder Over a year ago

@HadeS I have made your suggested changes, however I still get these errors: Client.cpp: In function ‘int main(int, char**)’: Client.cpp:33: error: invalid conversion from ‘void* ()(std::string)’ to ‘void* ()(void)’ Client.cpp:33: error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* ()(void), void*)’ ... Do I have to do some kind of casting? That line 33 error refers to where the pthread_create is

HadeS Over a year ago

@Masterminder sorry for small mistake... changes return type from void to void *.. try now..

|

Charles0429 · Accepted Answer · 2014-03-03 15:22:14Z

0

I think there may be two problems in your code

callback_function of thread is wrong

void *readerT(string *temp)

to

void *readerT(void *temp)
use join function in main thread

If you don't do it, the main thread will soon quit after creating the read_in thread, so use a join function to wait the thread to complete.

answered Mar 3, 2014 at 15:22

Charles0429

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