我有一个结构
struct {
int size;
char *data;
}tmp_buf;
现在我想为共享内存中的结构分配内存(mmap-ed location)
我的main()中有一个类型为“tmp_buf”的指针“tp” 当我尝试在位置“tp-> data”处使用strncpy()时,它会产生分段错误。
我有大小的mmap-ed共享内存(sizeof(struct tmp_buf)+ length_of_data)
This is the code i'm running:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <semaphore.h>
#include <sys/mman.h>
void * create_shared_memory(char *name, int size) {
int *ptr;
int ret;
int fd = shm_open (name, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
if (fd == -1) {
perror ("shm_open error!");
exit (1);
}
ret = ftruncate (fd, sizeof (size));
if (ret == -1) {
perror ("ftruncate error!");
exit (2);
}
ptr = mmap(0, sizeof (size), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (ptr == MAP_FAILED) {
perror ("shm-mmap error!");
exit (3);
}
return ptr;
}
typedef struct {
int size;
char *data;
}tmp_buf;
int main (int argc, char **argv)
{
tmp_buf *buf_ptr;
if(argc != 2)
{
perror("Error: Incorrect number of arguments passed\n");
exit(EXIT_FAILURE);
}
int max_buffers = atoi(argv[1]);
buf_ptr = (struct tmp_buf*)create_shared_memory("my_shm_buffer",sizeof(tmp_buf) + max_buffers*1024);
printf("Shared Memory Location: %p\n", buf_ptr);
printf("Shared Memory size: %d\n", buf_ptr->size);
printf("Shared Memory data: %s\n", buf_ptr->data);
buf_ptr->size =1;
printf("Shared Memory size: %d\n", buf_ptr->size);
printf("SIZEOF(int) =%d SIZEOF(char*) = %d\n",sizeof(int), sizeof(char*));
printf("Shared Memory size address: %p\n", (void*)&(buf_ptr->size));
printf("Shared Memory data address: %p\n", (void*)&(buf_ptr->data));
strncpy(buf_ptr->data,"Hello\n", 6);
printf("Shared Memory data: %s\n", buf_ptr->data);
return 0;
}
我看到的输出是这样的:
Shared Memory Location: 0x7ffff7ff6000
Shared Memory size: 0
Shared Memory data: (null)
Shared Memory size: 1 (After t->size = 1)
Shared Memory size address: 0x7ffff7ff6000
Shared Memory data address: 0x7ffff7ff6008
Segmentation fault (core dumped) (After strncpy("Hello\n",tp->data, 6))
答案 0 :(得分:3)
你试过吗
strncpy(buf_ptr->data, "Hello\n\0", 7);
你应该使用strncpy和(dest,src,len)而不是(src,dest,len)
C库函数char * strncpy(char * dest,const char * src,size_t n)从指向的字符串中复制最多n个字符,由src复制到dest。在src的长度小于n的长度的情况下,dest的余数将用空字节填充。
答案 1 :(得分:2)
这一行证明了最明显的问题:
sizeof(size)
sizeof(int)
不会太多,因为它会是size
给你的。为了使它达到你想要的大小,你只需传递ret = ftruncate (fd, size);
即可......
size
然后,您对此行重复同样的问题,该行也应该sizeof(size)
而不是ptr = mmap(0, sizeof (size), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
size
可能值得更改函数声明,使size_t
属于tmp_buf *
类型并让它返回void *
。转换返回的buf_ptr
不会自动导致它使用有效值填充tmp_buf* create_shared_memory(char *name, size_t size) {
tmp_buf *ptr;
int ret;
int fd = shm_open (name, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
if (fd == -1) {
perror ("shm_open error!");
exit (1);
}
ret = ftruncate (fd, size);
if (ret == -1) {
perror ("ftruncate error!");
exit (2);
}
ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (ptr == MAP_FAILED) {
perror ("shm-mmap error!");
exit (3);
}
ptr->size = size;
ptr->data = ((char *) ptr) + sizeof(ptr->size);
return ptr;
}
。最终结果应该看起来像
$ rpm -ql zabbix-sender
/usr/bin/zabbix_sender
...