在While循环中初始化Pthread

Question

im starting to use pthreads cpp library to resolve some homeworks.

In one of those, i do have to create a thread for each file named from 1 to T (T is fixed with Define as a positive integer), and this thread must process some informations of this file.

Actually, my thinking is to put a while loop in Main, like this:

pthread_t threads[T];

void *imprime(void *arg) {

    int a=-1, b=-1;
    string* t = reinterpret_cast<std::string*>(arg); //Recovering str
    string name = *t;
    cout<<"\nName: "<<name<<endl;
    ifstream inFile(nome.c_str());
    while(inFile>>a) {
            inFile>>b;
            cout<<"a: "<<a<<"\nb: "<<b<<endl;
    }
}

int main() {

    int lim = 1;
    string nome;
    int a = 0, b = 0;

    while(lim <= T) {
        nome = to_string(lim);
        cout<<"Opening: "<<lim<<endl;
        pthread_create(&threads[lim], NULL, &imprime, (void *)&nome);

        lim++;
    }
    cin.get();

    return 0;
}

At first, the thread didnt run, nothing happened. So, i put the "cin.get()" under the while and it suddently works (What i didnt understood yet).

But now, if T is 1 it works properly, but if T > 1, it doesnt work like it supposed to work.

I put two files(names 1, 2 and 3; with ints 'a' and 'b' separated by an space):

/* 
   File '1' = "1 2"
   File '2' = "3 4"
   File '3' = "5 6"
*/

and thats the output:

Opening: 1
Opening: 2
Opening: 3

Nome: 3
a: 5
b: 6

Nome: 3
a: 5
b: 6

Nome: 3
a: 5
b: 6

By some reason, the program runs the entire while T times before starting the threads, and it overwrite every thread with the last one.

What can i do?

Answer 1

Passing a pointer to nome is a bad idea as you can't be sure the individual thread copies the value before you change it again in main .

Make an array for the argument to the threads:

string threads_args[T];

and then do

    threads_args[lim] = to_string(lim);
    cout<<"Opening: "<<lim<<endl;
    pthread_create(&threads[lim], NULL, &imprime, (void *)&threads_args[lim]);

Further notice:

1) You should join the threads in main instead of using cin.get

2) while(lim <= T) shall be while(lim < T) . Currently you access outside array boundary. Also you probably want lim to start from 0 instead of 1 and then have threads_args[lim] = to_string(lim+1);

3) C++11 has std::thread which seems a better choice than pthread