C语言结构体数组，元素交换失败

问题遇到的现象和发生背景

何钦铭《C语言程序设计（第四版）》 P235第五题，执行swap（）后结构变量只有name发生了交换，其他结构体成员没有交换

问题相关代码，请勿粘贴截图

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
struct bd{
char year[5];
char month[3];
char day[3];
char* hisbirthday;
};
struct message{
char name[10];
struct bd birthday;
char phoneNumber[12];
};
void bubble(struct message* messages,int n);
void swap(struct message a , struct message b);
int main()
{
int n,i;
printf("输入人数：");
scanf("%d",&n);
struct message messages=(struct message)malloc(n*sizeof(struct message));
for(i=0;i<n;i++){
printf("输入第%d个人的姓名：",i+1);
scanf("%s",&messages[i].name);
printf("输入第%d个人的出生年份：",i+1);
scanf("%s",&messages[i].birthday.year);
printf("输入第%d个人的出生月份：",i+1);
scanf("%s",&messages[i].birthday.month);
printf("输入第%d个人的出生日：",i+1);
scanf("%s",&messages[i].birthday.day);
printf("输入第%d个人的手机号码：",i+1);
scanf("%s",&messages[i].phoneNumber);
char temp=strcat(messages[i].birthday.year,messages[i].birthday.month);
messages[i].birthday.hisbirthday=strcat(temp,messages[i].birthday.day);
// printf("here:%s\n",messages[i].birthday.hisbirthday);
}
bubble(messages,n);
for(i=0;i<n;i++){
printf("第%d个人的姓名：%s\n",i+1,messages[i].name);
printf("第%d个人的出生日期：%s\n",i+1,messages[i].birthday.hisbirthday);
}
free (messages);
return 0;
}
void bubble(struct message messages,int n)
{
int i,j,t;
for(i=1;i<n;i++){
for(j=0;j<n-i;j++){
if(strcmp(messages[j].birthday.hisbirthday,messages[j+1].birthday.hisbirthday)){
swap( &messages[j],&messages[j+1] );

        }
    }
}

}
void swap(struct message *a , struct message *b)
{
struct message temp ;
temp = *a ;
*a = *b ;
*b = temp ;
}

运行结果及报错内容

我的解答思路和尝试过的方法

通过对messages[i].birthday.hisbirthday大小的比较，实现对messages数组的冒泡排序，使数组元素按年龄从大到小的顺序排列

我想要达到的结果

数组元素按年龄从大到小的顺序排列

复制了你的代码，有报错，我进行了一些修改，修改之后代码参考如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct bd{
    char year[5];
    char month[3];
    char day[3];
    char* hisbirthday;
};
struct message{
    char name[10];
    struct bd birthday;
    char phoneNumber[12];
};
void bubble(struct message* messages,int n);
void swap(struct message *a , struct message *b);
char *appendBirthday(char *year, char *month, char *day);

int main(int argc, const char * argv[]) {
    int n,i;
    printf("输入人数：");
    scanf("%d",&n);
    struct message *messages=(struct message*)malloc(n*sizeof(struct message));
    for(i=0;i<n;i++){
        printf("输入第%d个人的姓名：",i+1);
        scanf("%s",messages[i].name);
        printf("输入第%d个人的出生年份：",i+1);
        scanf("%s",messages[i].birthday.year);
        printf("输入第%d个人的出生月份：",i+1);
        scanf("%s",messages[i].birthday.month);
        printf("输入第%d个人的出生日：",i+1);
        scanf("%s",messages[i].birthday.day);
        printf("输入第%d个人的手机号码：",i+1);
        scanf("%s",messages[i].phoneNumber);
        messages[i].birthday.hisbirthday= appendBirthday(messages[i].birthday.year,messages[i].birthday.month,messages[i].birthday.day);
         printf("here:%s\n",messages[i].birthday.hisbirthday);
    }
    bubble(messages,n);
    for(i=0;i<n;i++){
        printf("第%d个人的姓名：%s\n",i+1,messages[i].name);
        printf("第%d个人的出生日期：%s\n",i+1,messages[i].birthday.hisbirthday);
    }
    free (messages);
    
    return 0;
}

char *appendBirthday(char *year, char *month, char *day) {
    char *bir =(char *)malloc(sizeof(char));
    int i = 0;
    int j = 0;
    while (year[i] != '\0') {
        bir[j] = year[i];
        i++;
        j++;
    }
    i = 0;
    while (month[i] != '\0') {
        bir[j] = month[i];
        i++;
        j++;
    }
    i = 0;
    while (day[i] != '\0') {
        bir[j] = day[i];
        i++;
        j++;
    }
    bir[j] = '\0';
    return bir;
}

void bubble(struct message *messages,int n) {
    
    int i,j;
    for(i=1;i<n;i++){
        for(j=0;j<n-i;j++){
            if(strcmp(messages[j].birthday.hisbirthday,messages[j+1].birthday.hisbirthday)){
                swap(&messages[j], &messages[j+1]);
            }
        }
    }
}
void swap(struct message *a , struct message *b) {
    
    struct message temp ;
    temp = *a ;
    *a = *b ;
    *b = temp ;
}