如何存储输入列表以进行多线程编程

Question

Currently my program should take a list of numbers entered by the user at the command line and then find the sum of this numbers and print it out. My code is the following, I know to store a single number entered by the user, but what if I want a list of number, separated by space?

#include <pthread.h>
#include <stdio.h>
int sum; /* this data is shared by the thread(s) */
void *runner(char **); /* threads call this function */
int main(int argc, char *argv[])
{
pthread_t tid; /* the thread identifier */
pthread_t tid2;

pthread_attr_t attr; /* set of thread attributes */

if (argc != 2) {
fprintf(stderr,"usage: a.out <integer values>\n");
return -1;
}

pthread_attr_init(&attr);

pthread_create(&tid,&attr,(void(*)(void *))(runner),(void *)(argv+1));

pthread_join(tid,NULL);

printf("sum = %d\n",sum);
}
/* The thread will begin control in this function */
void *runner(char **param)
{
int i;
sum = 0;
for (i = 1; i <= 5; i++)
   sum = sum + atoi(param[i]);

pthread_exit(0);
}

I want to be able to enter a list of numbers in the command line, and store those numbers into a list and then find the sum of all those numbers.

, can someone tell me what is the correct way to do this?

Answer 1

It baffles me that you could write a threaded programme but did not know that:

you cannot cast parse an array of string to an array of int. you have to do the casts parsing one by one, during the sum loop.

/* The thread will begin control in this function */
void *runner(char **param)
{
int i;

sum = 0;
for (i = 1; i <= upper; i++)
    sum = sum + atoi(param[i]);
pthread_exit(0);
}

You also need to pass argv+1 and not argv[1] to pthread_create in main :

// the runner function declaration
void *runner(char **);

// the thread creation
pthread_create(&tid,&attr,(void *(*)(void *))(runner),(void *)(argv+1));

Answer 2

Some problems here:

if (argc != 2)

This means you're expecting the integer values to be quoted, ie a.out "1 2 3 4 5" . If you do things this way the numbers are represented as a single string, ie argv[1] := "1 2 3 4 5" .

It's easier to check for argc < 2 and taking the arguments as a.out 1 2 3 4 5 . This way each argument gets its own string, ie argv[1] := "1", argv[2] := "2" etc.

You can of course use a quoted list instead, but then you have add some logic to extract the integers from the string (eg with strtok ) whereas argument handling can do it for you instead.

Second, your program expects at least six integers here, and also skips the first one (you want i to go from 0 :

for (i = 1; i <= 5; i++)
   sum = sum + atoi(param[i]);

As for the upper limit, one way to convey the number of integers together with their strings is to use a struct:

struct arg_struct {
    int argc;
    char **argv;
};

and then use such a struct when calling pthread_create , ie

struct arg_struct args = { argc-1, argv+1 };
pthread_create(&tid,&attr,(void(*)(void *))(runner),(void *)(&args));

and change runner accordingly:

void *runner(struct arg_struct *param)
{
int i;
sum = 0;
for (i = 0; i < param->argc; i++)
   sum = sum + atoi(param->argv[i]);

pthread_exit(0);
}

Here's the code with all changes:

#include <pthread.h>
#include <stdio.h>

struct arg_struct {
    int argc;
    char **argv;
};

int sum; /* this data is shared by the thread(s) */
void *runner(struct arg_struct *); /* threads call this function */
int main(int argc, char *argv[])
{
pthread_t tid; /* the thread identifier */
pthread_t tid2;

pthread_attr_t attr; /* set of thread attributes */

struct arg_struct args = { argc-1, argv+1 };

if (argc < 2) {
fprintf(stderr,"usage: a.out <integer values>\n");
return -1;
}

pthread_attr_init(&attr);

pthread_create(&tid,&attr,(void *(*)(void *))(runner),(void *)(&args));

pthread_join(tid,NULL);

printf("sum = %d\n",sum);
}
/* The thread will begin control in this function */
void *runner(struct arg_struct *param)
{
int i;
sum = 0;
for (i = 0; i < param->argc; i++)
   sum = sum + atoi(param->argv[i]);

pthread_exit(0);
}