PThread library

[digi123]

I would like to ask that PrintHello accepts a void pointer but how come you can equate it to an integer directly ???
" tid = (int)threadid; "
while at the same time instead if a pointer a normal variable was passed into this function
" pthread_create(&threads[t], NULL, PrintHello, (void *)t); "

the above construct is taken from
https://computing.llnl.gov/tutorials...ssingArguments

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5
 
void *PrintHello(void *threadid)
{
int tid;
tid = (int)threadid;
printf("Hello World! It's me, thread #%d!\n", tid);
pthread_exit(NULL);
}
 
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc, t;
for(t=0; t<NUM_THREADS; t++){
printf("In main: creating thread %d\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
 
 

[JosAH]

@digi123
When you create a thread you can pass the address of a thread local chunk of memory to the newly created thread. The author of the example code wanted to have a cheap thread identification so s/he passed a simple integer.

A struct with an int containing the thread id could've been passed instead but this code saves a few lines I guess. Note that the conversion from an int to a void pointer (and vice versa) is implementation defined.

kind regards,

Jos

[digi123]

thanks i got my answer ------
i hope you meant to say 'undefined' i guess

[JosAH]

@digi123
Nope, I meant "implementation defined", i.e. an implementation can convert between the two types however it pleases but it should do it consistently.

kind regards,

Jos

[digi123]

thank you sir,
i got whole new perspective to look at