C：打印在共享内存中声明的数组时获取垃圾字符

Question

我正在尝试将一个字符串数组声明到共享内存中。 server.c 创建共享内存，client.c 填充数组 "tab" 并打印 it.And 它在客户端工作得很好。但是当运行 server.c !

时我得到垃圾字符

如有任何帮助，我们将不胜感激！

server.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>


typedef struct People
{
  char *tab[5];

  } Person;
  int i;

  int main()
{   
system("clear");
Person aaron;
Person *p_aaron;
int id;
int key = 12345;

p_aaron = &aaron;

if ((id = shmget(key,1000, IPC_CREAT | 0666)) < 0)
{
    perror("SHMGET");
    exit(1);
}
printf("server: size: %d \n", sizeof(aaron));

if((p_aaron = shmat(id, NULL, 0)) == (Person *) -1)
{
    perror("SHMAT");
    exit(1);
}

 for(i=0;i<5;i++) {
   printf("server tab: %s \n", p_aaron->tab[i]);

}

return 0;
}

client.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <string.h>

typedef struct People
{
char *tab[5];

} Person;
int test;
int i;

int main()
{   

system("clear");

Person aaron;
Person *p_aaron;
int id;
int key = 12345;

p_aaron = &aaron;

id = shmget(key,1000, IPC_CREAT | 0666);
p_aaron = shmat(id, NULL, 0);

    p_aaron->tab[0]="abnb";
    p_aaron->tab[1]="b";
    p_aaron->tab[2]="c";
    p_aaron->tab[3]="d";
    p_aaron->tab[4]="e";

 for(i=0;i<5;i++) {
   printf("client tab: %s \n", p_aaron->tab[i]);

}

return 0;
}

server.c输出

server tab: � 
server tab: � 
server tab: � 
server tab: � 
server tab: �

client.c输出

client tab: abnb 
client tab: b 
client tab: c 
client tab: d 
client tab: e

Answer 1

您用来初始化指针的文字字符串不在共享内存中，对服务器不可见。最简单的解决方案是声明一个字符串数组 char tab[5][MAXLEN] 并使其共享（MAXLEN 是最长元素的长度 + 1）。

Answer 2

扩展@DYZ 的回答正如 DYZ 所建议的那样，您的字符串文字对服务器不可见。尝试使用如下数组：

common.h

#ifndef _COMMON_H_
#define _COMMON_H_

#define MAX_CHAR    10
typedef struct People
{
char tab[5][MAX_CHAR];

} Person;

#endif /* _COMMON_H_ */

client.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <string.h>
#include "common.h"

int test;
int i;

int main()
{

    Person aaron;
    Person *p_aaron;
    int id;
    int key = 12345;

    p_aaron = &aaron;

    id = shmget(key,1000, IPC_CREAT | 0666);
    p_aaron = shmat(id, NULL, 0);

    snprintf(p_aaron->tab[0],MAX_CHAR,"%s","abnb");
    snprintf(p_aaron->tab[1],MAX_CHAR,"%s","bcde");
    snprintf(p_aaron->tab[2],MAX_CHAR,"%s","c");
    snprintf(p_aaron->tab[3],MAX_CHAR,"%s","d");
    snprintf(p_aaron->tab[4],MAX_CHAR,"%s","e");
    for(i=0;i<5;i++) {
        printf("client tab: %s \n", p_aaron->tab[i]);

    }

    return 0;
}

server.c

#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include "common.h"

int i;

int main()
{
    system("clear");
    Person aaron;
    Person *p_aaron;
    int id;
    int key = 12345;

    p_aaron = &aaron;

    if ((id = shmget(key,1000, IPC_CREAT | 0666)) < 0)
    {
        perror("SHMGET");
        exit(1);
    }
    printf("server: size: %lu \n", sizeof(aaron));

    if((p_aaron = shmat(id, NULL, 0)) == (Person *) -1)
    {
        perror("SHMAT");
        exit(1);
    }

    for(i=0;i<5;i++) {
        printf("server tab: %s \n", p_aaron->tab[i]);

    }

    return 0;
}

C：打印在共享内存中声明的数组时获取垃圾字符

C: Getting garbage characters when printing an array declared in shared memory

c

unix

arrays

shared-memory