Linux thread pthread

A small Linux pthread example:

#include <unistd.h>#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <fcntl.h>#include <string.h>int count = 0;void* pthread_fun(void* ptr){    count++;    sleep(1);    printf("count: %d\n", count);    return ptr;}int main(int argc, char* argv[]){    int num = 20;    int i = 0;    int ret = 0;    void* pt_ret[64];    pthread_t pt_id[64];    for(i=0; i<=num; i++)    {        ret = pthread_create(&pt_id[i], NULL, pthread_fun, NULL);        if(ret != 0)        {            perror("pthread_create failed");        }    }    for(i=0; i<=num; i++)    {        ret = pthread_join(pt_id[i], &pt_ret[i]);        if(ret != 0)        {            perror("pthread_join failed");        }    }    return 0;}

Compile and run:

gcc -o test -lpthread test.c./test

It seems OK!

However, after this change, there will be a problem:

#include <unistd.h>#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <fcntl.h>#include <string.h>void* pthread_fun(void* ptr){    int count = *ptr;    printf("count: %d\n", count);    sleep(1);    return ptr;}int main(int argc, char* argv[]){    int num = 20;    int i = 0;    int ret = 0;    void* pt_ret[64];    pthread_t pt_id[64];    for(i=0; i<=num; i++)    {        ret = pthread_create(&pt_id[i], NULL, pthread_fun, &i);        if(ret != 0)        {            perror("pthread_create failed");        }    }    for(i=0; i<=num; i++)    {        ret = pthread_join(pt_id[i], &pt_ret[i]);        if(ret != 0)        {            perror("pthread_join failed");        }    }    return 0;}

Compilation error:

# gcc -o test -lpthread test.c tmp.c: In function ‘pthread_fun’:tmp.c:10: warning: dereferencing ‘void *’ pointertmp.c:10: error: void value not ignored as it ought to be

Troubleshooting ......