GMP convert char array to float

Question

I am using GMP and MPI to calculate precision PI. Currently I have calculated PI in a worker process and need to send it back to the farmer process, to do this I have converted to a char array as so

mp_exp_t exp; 
pi_str = mpf_get_str(pi_str,
                         &exp,
                         10,
                         (size_t)PRECISION,
                         pi);

char send_str[3026]= {0};
strcpy(send_str,pi_str);                      

MPI_Send(&send_str, len, MPI_CHAR, 0, 1, MPI_COMM_WORLD);

This works fine, now I receive the char array and I need to perform other calcualtions so the char array needs converting back to a float.

char recv_str[3026] = {0};
    for(i=1; i<size ; i++)
    {
       printf("farmer**%d\n",size);
       MPI_Recv(&recv_str,3026, MPI_CHAR, i, 1,MPI_COMM_WORLD,  &status);
       printf("pi after send %s", recv_str);
       mpf_set_str(pi_ret, recv_str, 10);  
       gmp_printf("setting from string to float %.Ff\n", pi_ret, 20); 

This gives me a memory allocation fault, but I can not see another way of converting back to a float unless I am missing something.

Answer 1

You need to initialize pi_ret before assigning a value to it.

The easiesst way to do this would be with the mpf_init_set_str() function, which simultaneously initializes a floating point number and assigns its value from a string of chars.