返回信息流/*第一个程序主要是用来将用户输入的字符串修改共享内存断的值*/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/shm.h>
#include "shm_com.h"
int main()
{
int running = 1;
void *shared_memory = (void *)0;
struct shared_use_st *shared_stuff;
char buffer[BUFSIZ];
int shmid;
shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT);
if (shmid == -1) {
fprintf(stderr, "shmget failed\n");
exit(EXIT_FAILURE);
}
shared_memory = shmat(shmid, (void *)0, 0);
if (shared_memory == (void *)-1) {
fprintf(stderr, "shmat failed\n");
exit(EXIT_FAILURE);
}
[u][b]printf("Memory attached at %X\n", (int)shared_memory);[[/u]/b]
shared_stuff = (struct shared_use_st *)shared_memory;
while(running) {
while(shared_stuff->written_by_you == 1) {
sleep(1);
printf("waiting for client...\n");
}
printf("Enter some text: ");
fgets(buffer, BUFSIZ, stdin);
strncpy(shared_stuff->some_text, buffer, TEXT_SZ);
shared_stuff->written_by_you = 1;
if (strncmp(buffer, "end", 3) == 0) {
running = 0;
}
}
if (shmdt(shared_memory) == -1) {
fprintf(stderr, "shmdt failed\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
/*第二个程序用来打印被修改的内存段的值*/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/shm.h>
#include "shm_com.h"
int main()
{
int running = 1;
void *shared_memory = (void *)0;
struct shared_use_st *shared_stuff;
int shmid;
srand((unsigned int)getpid());
shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT);
if (shmid == -1) {
fprintf(stderr, "shmget failed\n");
exit(EXIT_FAILURE); }
/* We now make the shared memory accessible to the program. */
shared_memory = shmat(shmid, (void *)0, 0);
if (shared_memory == (void *)-1) {
fprintf(stderr, "shmat failed\n");
exit(EXIT_FAILURE);
}
printf("Memory attached at %X\n", (int)shared_memory);
/* The next portion of the program assigns the shared_memory segment to shared_stuff,
which then prints out any text in written_by_you. The loop continues until end is found
in written_by_you. The call to sleep forces the consumer to sit in its critical section,
which makes the producer wait. */
shared_stuff = (struct shared_use_st *)shared_memory;
shared_stuff->written_by_you = 0;
while(running) {
if (shared_stuff->written_by_you) {
printf("You wrote: %s", shared_stuff->some_text);
sleep( rand() % 4 ); /* make the other process wait for us ! */
shared_stuff->written_by_you = 0;
if (strncmp(shared_stuff->some_text, "end", 3) == 0) {
running = 0;
}
}
}
/* Lastly, the shared memory is detached and then deleted. */
if (shmdt(shared_memory) == -1) {
fprintf(stderr, "shmdt failed\n");
exit(EXIT_FAILURE);
}
if (shmctl(shmid, IPC_RMID, 0) == -1) {
fprintf(stderr, "shmctl(IPC_RMID) failed\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
/*下面是shm_com.h的内容*/
#define TEXT_SZ 2048
struct shared_use_st {
int written_by_you;
char some_text[TEXT_SZ];
};
为什么这两个程序输出Memory attached at那一行的结果不一样呢？？？
这两个程序是Linux程序设计第三版的示例程序，我看到书本上给的结果是一样的
这是一条镜像帖。来源：北邮人论坛 / embedded-system / #14244同步于 2013/12/4
Embedded_System机器人发帖
为什么两个相关联的共享内存程序输出的内存地址不一样
lishenan2008
2013/12/4镜像同步0 回复
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