pthread_create error

for ( int i=0; i<10; i++)
cout << "a";
}
>
void print_b(){
for ( int i=0; i<10; i++)
cout << "b";
}
>
>
int main(){
>
pthread_t thr_a_ID;
pthread_create ( &thr_a_ID, NULL, print_a, NULL );
>
pthread_t* thr_b_ID;
pthread_create ( &thr_b_ID, NULL, print_b, NULL );
}
//**************** code end ****************
>
**************** error ****************
main.cpp:23: error: invalid conversion from 'void (*)()' to 'void*
(*)(void*)'
main.cpp:23: error: initializing argument 3 of 'int
pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*),
void*)'
main.cpp:26: error: cannot convert 'pthread_t**' to 'pthread_t*'
for argument '1' to 'int pthread_create(pthread_t*, const
pthread_attr_t*, void* (*)(void*), void*)'
>
make: *** [main.o] Error 1
************************************************** **************

pthread_t* thr_b_ID;

>
I don't know anything about pthreads, but here's what your compiler is
telling you:
>
Error on line 23:
print_a needs to look like this:
>
void* print_a(void* data) {
// Do something and return something
}
>
Error on line 26:Get rid of *.
>
Michael

thanks,
I fixed the code but it is not doing what I expected it to do, which
is print out aa(s) and bb(s).

"Michael" <mchlgibs@aol.comwrites:
>>
thanks,
I fixed the code but it is not doing what I expected it to do, which
is print out aa(s) and bb(s).
>
//**************** code v 1.0 start ****************
#include <iostream>
#include <ctime>
#include <cstdio>
#include <cstdlib>
#include <pthread.h>
>
using namespace std;
>
void* print_a(void* data) {
char* a = (char*) data;
for ( int i=0; i<10; i++)
cout << *a;
}
>
void* print_b(void* data){
char* b = (char*) data;
for ( int i=0; i<10; i++)
cout << *b;
}
>
>
int main(){
char* a = "aa";

void * pva = (void*) a;
pthread_t thr_a_ID;
pthread_create ( &thr_a_ID, NULL, print_a, pva );

>
char* b = "bb";
void* pvb = (void*) b;
pthread_t thr_b_ID;
pthread_create ( &thr_b_ID, NULL, print_b, pvb );
}
//**************** code v 1.0 end ****************

here is the makefile to run the code
>
LDFLAGS = -lpthread
CXXFLAGS = -gdwarf-2
OBJS := $(patsubst %.cpp,%.o,$(wildcard *.cpp))
COMP = g++
>
proj: $(OBJS)
$(COMP) -Wall -gdwarf-2 -o proj $(OBJS) $(LDFLAGS)
>
#-Wall turns on all warnings
#-gdwarf-2 for dubugging note gdb manual 12.4.1
clean:
rm -rf *.o proj

Gary Wessle wrote:>
[Off Topic]
>
Instead of printing from seperate threads, where a race condition can
diffuse the output if not outright fail, lets have a couple of threads
do a little work instead.
>
#include <iostream>
#include <pthread.h>
>
// this function will load a char array[10] with chars from a to j
void* load_carray(void* p_data)
{
char* p_array = static_cast<char*>(p_data);
char c = 'a';
for (int i=0; i< 10; i++)
*(p_array++) = c++;
return 0;
}
>
// this function loads an int array[10] from 0 to 9
void* load_narray(void* p_data)
{
int* p_narray = static_cast<int*>(p_data);
for (int i=0; i< 10; i++)
*(p_narray++) = i;
return 0;
}
>
// function prints any array - deduced parameters
template< typename T , const size_t Size>
void print_t(T(&array)[Size])
{
for(size_t i = 0; i < Size; ++i)
{
std::cout << array[i];
}
std::cout << std::endl;
}
>
int main()
{
char carray[10] = { 'z' }; // char[] for thread 0
int narray[10] = { 0 }; // int[] fot thread 1
// threadID array and result array
pthread_t threadID[2];
int result[2];
// create threads with PTHREAD_CREATE_JOINABLE - the default
result[0] = pthread_create( &threadID[0],
0, // PTHREAD_CREATE_JOINABLE
load_carray,
carray );
result[1] = pthread_create( &threadID[1],
0, // PTHREAD_CREATE_JOINABLE
load_narray,
narray );
// wait for both threads to be created and complete
pthread_join( threadID[0], 0);
pthread_join( threadID[1], 0);
// display threadID and results
for(int n = 0; n < 2; ++n)
{
std::cout << "threadID " << threadID[ n ];
std::cout << "\nresult: " << result[ n ] << std::endl;
}
// lets see the initialized arrays
print_t( carray );
print_t( narray );
>
return 0;
}
>
/*
threadID 1084229952
result: 0
threadID 1094719808
result: 0
abcdefghij
0123456789
*/

Gary Wessle <phddas@yahoo.comwrites:
>>
for the records:
the Fix:
>
#include <iostream>
#include <ctime>
#include <cstdio>
#include <cstdlib>
#include <pthread.h>
>
using namespace std;
>
void* print_a(void* data) {
pthread_yield(); // send to end of run queue
cout << "a called\n";
string* a = static_cast<string*(data);
for ( int i=0; i<10; i++) {
cout << *a;
pthread_yield();
}
cout << "--a finihed\n";
}
>
void* print_b(void* data){
cout << "b called\n";
string* b = static_cast<string*(data);
for ( int i=0; i<10; i++) {
cout << *b;
pthread_yield();
}
cout << "--b finihed\n";
}
>
int main(){
>
pthread_t thr_a_ID, thr_b_ID;
string a = "aa";
string b = "bb";
int iret1, iret2;
void * pva = static_cast<void*(&a);
void* pvb = static_cast<void*(&b);
>
iret1 = pthread_create ( &thr_a_ID, NULL, print_a, pva );
iret2 = pthread_create ( &thr_b_ID, NULL, print_b, pvb );
>
pthread_join (thr_a_ID, NULL);
pthread_join (thr_b_ID, NULL);
>
}