online program如何在编译期间使用pthread提供错误?
我确信我做错了,但我已经编译并运行该网站的其他程序。
我使用 gcc -pthread -o hello thread.c 命令编译程序。 有什么想法吗?
编译报告:
thread.c: In function ‘Hello’:
thread.c:23:24: warning: incompatible implicit declaration of built-in function ‘sin’ [enabled by default]
result = result + sin(i) * tan(i);
^
thread.c:23:33: warning: incompatible implicit declaration of built-in function ‘tan’ [enabled by default]
result = result + sin(i) * tan(i);
^
thread.c:25:4: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 2 has type ‘void *’ [-Wformat=]
printf("%ld: Hello World!\n", threadid);
^
thread.c: In function ‘main’:
thread.c:38:5: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
printf("Code %d= %s\n",rc,strerror(rc));
^
/tmp/ccmix2XI.o: In function `Hello':
thread.c:(.text+0x33): undefined reference to `sin'
thread.c:(.text+0x42): undefined reference to `tan'
collect2: error: ld returned 1 exit status
答案 0 :(得分:1)
它会抱怨,因为您没有包含math.h
并且没有与数学库建立链接。
包含`并编译为:
gcc -o hello thread.c -pthread -lm
您还需要:
#include <string.h> # for strerror() function
#include <unistd.h> # for sleep() function
您需要在printf()中将void*
转换为long
。
printf("%ld: Hello World!\n", (long)threadid);
请注意,此整数转换指针是实现定义。理想情况下,您应该将指针传递给long
并将其强制转换回long*
并取消引用它。它可以通过以下方式修改:
#include <math.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NTHREADS 32
void *Hello(void *threadid)
{
int i;
double result=0.0;
long my_id = *(long*)threadid;
sleep(3);
for (i=0; i<10000; i++) {
result = result + sin(i) * tan(i);
}
printf("%ld: Hello World!\n", my_id);
pthread_exit(NULL);
}
int main(int argc, char *argv[])
{
pthread_t threads[NTHREADS];
int rc;
long t;
long a[NTHREADS];
for(t=0;t<NTHREADS;t++){
a[t] = t;
rc = pthread_create(&threads[t], NULL, Hello, &a[t]);
if (rc){
printf("ERROR: return code from pthread_create() is %d\n", rc);
printf("Code %d= %s\n",rc,strerror(rc));
exit(-1);
}
}
printf("main(): Created %ld threads.\n", t);
pthread_exit(NULL);
}