我已经构建了一个程序,允许我创建和删除消息队列以及发送和接收消息 .
除接收消息外,一切似乎都正常工作 . 当我收到结构时,我可以访问该类型(我一直用来表示“收件人”)并打印它,但是存储在结构的msg字段中的字符串将不会打印 . 在使用msgrcv()之后,printf()似乎成功访问了mbuf.type字段,但没有访问mbuf.msg . 我已经尝试过调试以找出问题所在,但到目前为止我还没有成功 .
消息似乎被发送到队列,因为当我使用“ipcs -q”查看我的内核的消息队列时,它将正确显示我发送的消息数 . 我还能够在我发送消息的程序实例中访问和打印msg字段 . 直到程序退出并且我使用“-r”标志重新启动它,我才能打印msg字段 .
我已经包含了下面的代码,包括包含我的消息struct定义的头文件 .
请注意:我知道我的验证很笨重,我计划在程序正常工作后简化它 . 如果它令人困惑,我道歉 .
标头文件:
#ifndef MESSAGE_BUFFER
#define MESSAGE_BUFFER
#define MSG_MAX 4056
typedef struct messageBuffer
{
long recipient; //recipient of message
long senderID; //id number of the sender
char msg[MSG_MAX]; //content of the message
}messageBuffer;
#endif
主要:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/types.h>
#include "message.h"
//function to print usage information upon error
void printUsage(){
printf("Error: Invalid arguments\n");
printf("Usage:\n");
printf("(Create Queue) <-c/C> <key>\n");
printf("(Send a message) <-s/S> <key> <recipient_id> <message>\n");
printf("(Receive a message) <-r/R> <key> <recipient_id>\n"); printf("(Delete queue) <-d/D> <key>\n");
}
//main
int main(int argc, char **argv){
//declare necessary variables
char flag;
int msqid;
messageBuffer mbuf;
size_t buf_length;
int msgflg = IPC_CREAT | 0666;
key_t key;
unsigned long recipient;
//validate arguments
if((argc < 3 || argc > 5) || argv[1][0] != '-' || strlen(argv[1]) != 2){
printf("%d\n", argc);
printUsage();
return -1;
}
flag = argv[1][1];
switch(flag){
//Create a message queue
case 'c':
case 'C':
if((key = atoi(argv[2])) < 1){
printf("Error assigning key");
return -1;
}
if((msqid = msgget(key, msgflg)) < 1){
printf("Error creating queue:");
return -1;
}
printf("%s%i\n", "Key: ", key);
printf("%s%i\n", "msqid: ", msqid);
break;
//Send a message
case 's':
case 'S':
if((key = atoi(argv[2])) < 1){
perror("Error assigning key:");
return -1;
}
if((msqid = msgget(key, 0400)) < 1){
perror("Error accessing queue:");
}
mbuf.recipient = atoi(argv[3]);
strncpy(mbuf.msg, argv[4], MSG_MAX);
buf_length = strlen(mbuf.msg) + 1;
if(msgsnd(msqid, &mbuf, buf_length, 0) < 0){
perror("Error sending message:");
return -1;
}
printf("Message sent (%lu): %s\n", mbuf.recipient, mbuf.msg);
break;
//Receive a message
case 'r':
case 'R':
if((key = atoi(argv[2])) < 1){
perror("Error assigning key:");
return -1;
}
if((msqid = msgget(key, 0400)) < 1){
perror("Error accessing queue:");
}
recipient = atoi(argv[3]);
if( msgrcv(msqid, &mbuf, MSG_MAX, recipient, 0)< 0){
perror("Error receiving message:");
return -1;
}
printf("Message received (%lu):\n", mbuf.recipient);
printf("%s\n", mbuf.msg);
break;
//Delete a message queue
case 'd':
case 'D':
if((key = atoi(argv[2])) < 1){
perror("Error assigning key");
return -1;
}
if((msqid = msgget(key, 0400)) < 1){
perror("Error accessing queue:");
}
printf("%d\n", msqid);
if((msgctl(msqid, IPC_RMID, NULL)) < 0){
perror("Delete message queue failed:");
}
break;
//invalid flag
default:
printUsage();
return -1;
}
return 0;
}
我很感激任何意见 . 谢谢 .
1 回答
事实证明,问题在于指定传递的结构的大小 . 我更改了代码“buf_length = strlen(mbuf.msg)1;” to buf_length =(sizeof(mbuf.msg)1);