C中的嵌套结构和指针

Question

编译器有两个抱怨：

错误：“打印输出”的参数1的类型不兼容

警告：预期的结构用户*但参数的类型为'users'

我该如何解决？ 并且请检查功能printout是否正常。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct{
   char username[25];
   char firstname[25];
   char lastname[25];
   int age;
}users;

typedef struct{
   users data;
   int id;
}publicusers;

users createuser(char *uname, char *fname, char *lname, int fage);
void printout(users *data);

int main(){
    printout(createuser("kway","minseon","huh", 25));
    return 0;
}

users createuser(char *uname, char *fname, char *lname, int fage){
    publicusers user1;
    strcpy(user1.data.username, uname);
    strcpy(user1.data.firstname, fname);
    strcpy(user1.data.lastname, lname);
    user1.data.age = fage;
    return user1.data;
}

void printout(users *data){
    printf("username:  %s\n",data->username);
    printf("firstname: %s\n",data->firstname);
    printf("lastname:  %s\n",data->lastname);
    printf("age:       %d\n",data->age);
}

Answer 1

您的createuser函数返回users类型，并且函数printout users*作为其参数，这是指向users的指针。

因为要在createuser函数中声明struct publicusers user1 ，所以不能将其地址作为返回值发送。 快速的解决方案是将函数定义从以下位置更改：

void printout(users *data);
void printout(users *data){
   printf("username:  %s\n",data->username);
   printf("firstname: %s\n",data->firstname);
   printf("lastname:  %s\n",data->lastname);
   printf("age:       %d\n",data->age);
}

至

void printout(users data);
void printout(users data){
   printf("username:  %s\n",data.username);
   printf("firstname: %s\n",data.firstname);
   printf("lastname:  %s\n",data.lastname);
   printf("age:       %d\n",data.age);
}

这将创建struct users的副本。 如果要避免创建副本，则应考虑在主目录中创建publicusers user1并将其作为附加参数发送给users createuser函数。

Answer 2

您的警告和错误消息是从以下行生成的：

printout(createuser("kway","minseon","huh", 25));

函数printout期望user *类型值作为其参数，但函数createuser返回user类型值。

要解决此问题，您应该使用&运算符将user *类型值作为参数传递。 将以上一行代码更改为两行代码：

users u = createuser("kway","minseon","huh", 25);
printout(&u);

---

还有另一种解决方法。 您可以将功能printout的参数类型从user *更改为user 。

您的代码应为：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct{
   char username[25];
   char firstname[25];
   char lastname[25];
   int age;
}users;

typedef struct{
   users data;
   int id;
}publicusers;

users createuser(char *uname, char *fname, char *lname, int fage);
void printout(users data);                     // parameter type changed

int main(){
    printout(createuser("kway","minseon","huh", 25));
    return 0;
}

users createuser(char *uname, char *fname, char *lname, int fage){
    publicusers user1;
    strcpy(user1.data.username, uname);
    strcpy(user1.data.firstname, fname);
    strcpy(user1.data.lastname, lname);
    user1.data.age = fage;
    return user1.data;
}

void printout(users data){                     // parameter type changed
    printf("username:  %s\n",data.username);   // -> operator changed to . operator
    printf("firstname: %s\n",data.firstname);  // -> operator changed to . operator
    printf("lastname:  %s\n",data.lastname);   // -> operator changed to . operator
    printf("age:       %d\n",data.age);        // -> operator changed to . operator
}