使用gcc时出现以下错误，我不确定是否可以解决未声明的错误。
V_TRAP.c：在“ my_func”函数中：
V_TRAP.c：168：22：错误：未声明“ a”（此功能的首次使用） partial_sum =（f（a）+ f（b））/ 2.0;
V_TRAP.c：168：22：注意：每个未声明的标识符对于出现在其中的每个函数仅报告一次
V_TRAP.c：168：29：错误：未声明“ b”（此功能首次使用） partial_sum =（f（a）+ f（b））/ 2.0; ^ V_TRAP.c：172：37：错误：未声明“ h”（此功能首次使用） partial_sum + = f（（a）+ i *（h））;
/*
* This version does not make use of any atomics.
*Input: a, b, n, num_threads
* Output: Estimate of integral from a to b of f(x)
* using n trapezoids, with num_threads.
* Compile: gcc -o trap V_TRAP.c -O3 -std=c99 -Wall -lpthread -lm
* Usage: ./V_TRAP
* */
#define _REENTRANT
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <math.h>
#include <pthread.h>//
#ifdef _WIN32
# define NOMINMAX
#endif
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <float.h>
#include <time.h>
/* Data structure defining what to pass to each worker thread. */
typedef struct thread_data_s {
int tid; /* The thread ID. */
float a; /* Pointer to a. */
float b; /* Pointer to b. */
int num_trapezoids; /* Number of trapezoids in the
float h; /* Pointer to base lenght of trapezoid */
int num_threads; /* Number of threads in the pool. */
int offset; /* Starting offset for each thread
int chunk_size; /* Chunk size. */
double *partial_sum; /* Starting address of the partial_sum array. */
} thread_data_t;
/* Function prototypes. */
double compute_using_pthreads (float , float , int, float , int);
void *my_func (void *);
void print_args (thread_data_t *);
int
main (int argc, char **argv)
{
if (argc < 5) {
printf ("Usage: trap lower-limit upper-limit num-trapezoids
num- threads\n");
printf ("lower-limit: The lower limit for the integral\n");
printf ("upper-limit: The upper limit for the integral\n");
printf ("num-trapezoids: Number of trapeziods used to
approximate the area under the curve\n");
printf ("num-threads: Number of threads to use in the
calculation\n");
exit (EXIT_FAILURE);
}
float a = atof(argv[1]); /* Lower limit */
float b = atof(argv[2]); /* Upper limit */
float num_trapezoids = atof(argv[3]); /* Number of trapezoids */
float h = (b - a)/num_trapezoids; /* Base of each trapezoid */
printf ("The base of the trapezoid is %f \n", h);
/* Compute the using the multi-threaded solution. */
int num_threads = atoi(argv[5]); /* Number of threads */
struct timeval start, stop;
gettimeofday (&start, NULL);
double mt_result = compute_using_pthreads (a, b,
num_trapezoids, h, num_threads);
gettimeofday (&stop, NULL);
printf ("Pthread solution = %f. \n", mt_result);
printf ("Execution time = %fs. \n", (float)(stop.tv_sec -
start.tv_sec +\
(stop.tv_usec - start.tv_usec)/(float)1000000));
printf ("\n");
/* Free memory here. */
//free ((void *) a);
//free ((void *) b);
pthread_exit (NULL);
}//------------------------------------- END OF MAIN
* Function: f
* Purpose: Defines the integrand
* Input args: x
* Output: sqrt((1 + x^2)/(1 + x^4))
*/
float
f (float x)
{
return sqrt ((1 + x*x)/(1 + x*x*x*x));
}
/* This function computes using pthreads. */
double
compute_using_pthreads (float a, float b, int num_trapezoids, float h,
int num_threads)
{
pthread_t *thread_id = (pthread_t *) malloc (num_threads * sizeof
(pthread_t)); /* Data structure to store the thread IDs. */
pthread_attr_t attributes; /* Thread attributes. */
pthread_attr_init (&attributes); /* Initialize the thread attributes
to
the default values. */
/* Allocate memory on the heap for the required data structures and
create the worker threads. */
int i;
double *partial_sum = (double *) malloc (sizeof (double) *
num_threads); /* Allocate memory to store partial sums returned by the
threads. */
thread_data_t *thread_data = (thread_data_t *) malloc (sizeof
(thread_data_t) * num_threads);
int chunk_size = (int) floor ((float) num_trapezoids/(float)
num_threads); /* Compute the chunk size. */
for (i = 0; i < num_threads; i++) {
thread_data[i].tid = i;
thread_data[i].a = a;
thread_data[i].b = b;
thread_data[i].num_trapezoids = num_trapezoids;
thread_data[i].h = h;
thread_data[i].num_threads = num_threads;
thread_data[i].offset = i * chunk_size;
thread_data[i].chunk_size = chunk_size;
thread_data[i].partial_sum = partial_sum;
}
for (i = 0; i < num_threads; i++)
pthread_create (&thread_id[i], &attributes, my_func, (void *)
&thread_data[i]);
/* Wait for the workers to finish. */
for (i = 0; i < num_threads; i++)
pthread_join (thread_id[i], NULL);
/* Accumulate partial sums. */
double sum = 0.0;
for (i = 0; i < num_threads; i++)
sum += partial_sum[i];
sum = sum*h;
/* Free dynamically allocated data structures. */
free ((void *) partial_sum);
free ((void *) thread_data);
return sum;
}
/* This function is executed by each thread to compute the overall
result. */
void *
my_func (void *args)
{
// /* Typecast the argument to a pointer to the thread_data_t
structure. */
thread_data_t *thread_data = (thread_data_t *) args;
/* Compute the partial sum that this thread is responsible for. */
double partial_sum = 0.0;
partial_sum = (f(a) + f(b))/2.0;
if (thread_data->tid < (thread_data->num_threads - 1)) {
for (int i = thread_data->offset; i < (thread_data->offset +
thread_data->chunk_size); i++)
partial_sum += f((a)+i*(h));
}
else { /* This takes care of the number of trapezoids that the
final thread must process. */
for (int i = thread_data->offset; i < thread_data->num_trapezoids;
i++)
partial_sum += f((a)+i*(h));
}
/* Store partial sum into the partial_sum array. */
thread_data->partial_sum[thread_data->tid] = partial_sum;
pthread_exit (NULL);
}
/* Helper function. */
void
print_args (thread_data_t *thread_data)
{
printf ("Thread ID: %d\n", thread_data->tid);
printf ("Numer of threads: %d\n", thread_data->num_threads);
printf ("Num trapezoids: %d\n", thread_data->num_trapezoids);
printf ("Address of vector A on heap: %p\n", &(thread_data->a));
printf ("Address of vector B on heap: %p\n", &(thread_data->b));
printf ("Offset within the vectors for thread: %d\n",
thread_data->offset);
printf ("Chunk size to operate on: %d\n", thread_data->chunk_size);
printf ("\n");
}
答案 0 :(得分：1)
函数a中不存在变量b，h和my_func，这就是为什么您会收到有关未声明标识符的错误的原因。 / p>
这些名称是thread_data_t的成员，该成员通过void *传递给此函数。您可能需要thread_data->a，thread_data->b和thread_data->h。