메시지큐를 이용한 프로그램에대해 질문을 드립니다....

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "msg_header.h"
 
void list_init(list_buf_t **head);	//링크드 리스트 초기화
int list_insert(FILE *file, list_buf_t **head);	//리스트 삽입
void list_all_print(list_buf_t **head);				//리스트 프린트
int list_search(msg_buf_t *msg, list_buf_t **head);	//리스트 검색 
int msg_receive(int msgq_receive_id, msg_buf_t *msg);
 
int main()
{
	int msg_prio;
	int msgq_receive_id;
	int res;
 	list_buf_t *list_head;
	msg_buf_t msg;
 
	res = 1;
	list_head = NULL;
	list_init(&list_head);
 
	msgq_receive_id = msgget(MSGQ_KEYSEND, IPC_CREAT | PERMISSION); //msgq생성
	if (msgq_receive_id == -1) {
		printf("메시지 큐 생성 실패\n");
		exit(1);
	}
 
	while (res == 1) {		//서버가 계속 가동 되도록 설정
		memset(msg.mtext, 0x00, MAX_LENGTH);
		res = msg_receive(msgq_receive_id, &msg);
		if (res == -1) {
			printf("메시지가 없습니다 \n");
			res = 1;
			continue;
		}
		list_search(&msg, &list_head);
 
	}
 
	if(msgctl(msgq_receive_id, IPC_RMID, 0) == -1){  // Remove msgq
		perror("msgq remove failed");
		exit(1);
	}
 
	return 0;
}
 
void list_init(list_buf_t **head)
{
	FILE *file;
 
	file = fopen("list.txt", "r");
	if (file == NULL) {
		perror("file open error!\n");
		exit(1);
	}
	while (feof(file) == 0) {
		list_insert(file, head);
	}
	fclose(file);	
	list_all_print(head);
}
 
int list_insert(FILE *file, list_buf_t **head)
{
	list_buf_t *tmp_buf;
	list_buf_t *new_buf;
 
	new_buf = (list_buf_t *)malloc(sizeof(list_buf_t));
	if (new_buf == NULL) {
		perror("메모리 부족\n");
		exit(1);
	}
 
	if (0 < fscanf(file, "%s %d %s %s %s ", new_buf->name, &new_buf->age,
			new_buf->rrn_num, new_buf->address, new_buf->phone_num)) {
 
		if (*head == NULL) {
			new_buf->next = NULL;
			*head = new_buf;
		} else {
			tmp_buf = *head;
			new_buf->next = tmp_buf;
			*head = new_buf;
		}
	}
	return 0;
}
 
void list_all_print(list_buf_t **head)
{
	list_buf_t *ptr;
 
	if (*head == NULL) {
		printf("no data!\n");
		return;
	}
 
	for (ptr = *head; ptr != NULL; ptr = ptr->next) {
		printf("======================================\n");
		printf("이름 : %s \n", ptr->name);
		printf("나이 : %d \n", ptr->age);
		printf("주민번호 : %s \n", ptr->rrn_num);
		printf("주소 : %s \n", ptr->address);
		printf("전화번호 %s \n", ptr->phone_num);
		printf("======================================\n");
 
	}
}
 
int list_search(msg_buf_t *msg, list_buf_t **head) 
{
	list_buf_t *ptr;
	int char_to_int;
	ptr = *head;
	while (ptr != NULL) {
		switch(msg->search_code) {
			case 1:
				if (strcmp(msg->mtext, ptr->name) == 0) {
					printf("dddd\n");	
 
					break;
				}
			case 2:
				char_to_int = atoi(msg->mtext);
				if(char_to_int == ptr->age) {
					printf("dddd\n");	
 
					break;
				}
			case 3:
				if(strcmp(msg->mtext, ptr->rrn_num) == 0) {
					printf("dddd\n");	
 
					break;
				}
			case 4:
				if(strcmp(msg->mtext, ptr->address) == 0) {
					printf("dddd\n");	
 
					break;
				}
			case 5:
				if(strcmp(msg->mtext, ptr->phone_num) == 0) {
					printf("dddd\n");	
 
					break;
				}
		}
		ptr = ptr->next;
	}
	return 0;
}
 
int msg_receive(int msgq_receive_id, msg_buf_t *msg)
{
	int indentifier;
 
	indentifier = msgrcv(msgq_receive_id, msg, 
			sizeof(msg_buf_t), 0, IPC_NOWAIT);
	if (indentifier == -1) {
		sleep(1);
		return -1;
	}
	printf("\n---> search_code: %ld content: %s\n", 
			msg->search_code, msg->mtext);
 
	return 1;
}

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>
#include <sys/stat.h>
#include <errno.h>
 
#define MSGQ_KEYSEND (key_t)1111
#define MSGQ_KEYREAD (key_t)2222
#define PERMISSION 0777
#define MAX_LENGTH 255
 
typedef struct _msg_buf {
	int search_code;
  	char mtext[MAX_LENGTH];
}msg_buf_t;
 
typedef struct _list_buf {
	char name [20];
	int age;
	char rrn_num[20];
	char address[40];
	char phone_num[20];
	struct _list_buf *next;
}list_buf_t;