How to extract substring from POSIX message? - c

Question

I have a server-client program, the client sends the server a message using a struct that has three major values: a date, and two timestamps.
Now, when the server receives the message, I try to extract the date from the message struct as a substring of the character array and then convert it to an int, but I've been stuck for hours now even trying to get the relevant characters from the message.
My server program:
#include "msg.h"
const char *months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
void delete_mq(char* mname, mqd_t qid) {
if (mq_close(qid) < 0) {
perror("Error closing queue");
exit(1);
}
if (mq_unlink(mname) < 0) {
perror("Error unlinking queue");
exit(1);
}
}
void make_command(MESSAGE *mess, char *mname, mqd_t qid) {
printf("making command, hehe\n");
if (strcmp(mess->date,"STOP") == 0){
printf("Stopping the server.\n");
delete_mq(mname, qid);
exit(0);
}
// this is where I am stuck
char thedate[3];
char *date = mess->date;
strncpy(thedate, date+1, 1);
thedate[2] = '\0';
printf("%s\n", thedate);
strcpy(mess->messtext,"Some text respone message");
}
int main(int argc, char** argv)
{
int flagsc = O_RDONLY | O_CREAT;
mode_t mode = 0600;
struct mq_attr attr;
attr.mq_flags = 0;
attr.mq_maxmsg = 10;
attr.mq_msgsize = sizeof(MESSAGE);
attr.mq_curmsgs = 0;
int flags = O_WRONLY;
char cname[10];
char sqname[15];
sprintf(sqname,"%s%s",qname,getlogin());
mqd_t qid = mq_open(sqname, flagsc, mode, &attr);
if (qid <0) {
perror("Error opening message queue");
exit(1);
}
for (;;) {
MESSAGE message;
unsigned int priority = 0;
if (mq_receive(qid, (char*) &message, sizeof(message), &priority) != -1) {
make_command(&message, qname, qid);
sprintf(cname,"/%d", message.pid);
message.pid = getpid();
mqd_t cmqid = mq_open(cname, flags);
mq_send(cmqid, (char*)&message, sizeof(MESSAGE), 0);
mq_close(cmqid);
}
}
mq_close(qid);
return 0;
}
My client program:
// ./client 11.23. 13:24 16:43
#include "msg.h"
int main(int argc, char** argv)
{
if (argc != 4){
printf("Usage: ./client <date e.g. 11.23.> <time1 e.g. 13:24> <time2 e.g. 16:43>\n");
exit(1);
}
int flags = O_WRONLY;
int cflags = O_RDONLY|O_CREAT;
mode_t mode = 0600;
char sqname[15];
sprintf(sqname,"%s%s", qname, getlogin());
mqd_t qid = mq_open(sqname, flags);
if (qid == -1) {
perror("Error opening queue in client");
exit(1);
}
struct mq_attr temp;
if (mq_getattr(qid, &temp) == -1) {
perror("Error with getattr in client");
} else {
// finish later
}
char cqname[20];
struct mq_attr attr;
attr.mq_flags = 0;
attr.mq_maxmsg = 8;
attr.mq_msgsize = sizeof(MESSAGE);
attr.mq_curmsgs = 0;
sprintf(cqname,"/%d", getpid());
mqd_t cqid = mq_open(cqname, cflags, mode, &attr);
if (cqid == -1) {
perror("Error opening queue in client");
exit(1);
}
MESSAGE mess;
strcat(mess.date, argv[1]);
strcat(mess.time1, argv[2]);
strcat(mess.time2, argv[3]);
mess.pid = getpid();
printf("Client has sent request");
if (mq_send(qid, (char*) &mess, sizeof(MESSAGE), 0) < 0) {
perror("Error sending message in client");
exit(1);
}
if (strcmp(mess.date,"STOP") != 0) {
if (mq_receive(cqid,(char*) &mess, sizeof(MESSAGE), 0) < 0) {
perror("Error receiving message in client");
exit(1);
}
} else {
printf("Stopping the client.\n");
if(mq_close(qid) < 0) {
perror("error closing server queue");
exit(1);
}
if(mq_close(cqid) < 0) {
perror("error closing client queue");
exit(1);
}
if (mq_unlink(cqname) < 0) {
perror("Error unlinking client queue");
exit(1);
}
exit(0);
}
printf("%s\n", mess.messtext);
if(mq_close(qid) < 0) {
perror("error closing server queue");
exit(1);
}
if(mq_close(cqid) < 0) {
perror("error closing client queue");
exit(1);
}
if (mq_unlink(cqname) < 0) {
perror("Error unlinking client queue");
exit(1);
}
exit(0);
}
And the header:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>
#include <mqueue.h>
#define KEY 1111
typedef struct{
int pid;
// e.g. 11.23.
char date[50];
char time1[50];
char time2[50];
char messtext[10];
} MESSAGE;
char * qname="/server_";
Now, the arguments for a client execution should be a date, and two timestamps. When the server receives the message, I want to extract the first two characters from date (the month) and convert it to int so that I could get the relevant month from *months[].
I tried pretty much everything: strcpy, memcpy, sprintf and I'm going nuts, because it will either only print the first number of the month, or won't convert correctly, or print extra crazy characters from memory, and I've barely started to break the message down into parts. The mess->date apparently has some other character on its first position, and I can't manage to skip it.
Could someone help me achieve what I described?