结构：未声明的标识符

Question

我试图在我的程序中使用结构，并收到一堆错误消息，指出time1，time2和hourDif是未声明的标识符。我以为我按照你应该的方式宣布了这些结构，所以我对这个问题是什么感到困惑。

下面的代码：

#include <stdio.h> 

struct time1 { 
    int seconds1; 
    int minutes1; 
    int hours1; 
}; 

struct time2 { 
    int seconds2; 
    int minutes2; 
    int hours2; 
}; 

    int timeDif(time1, time2) { 
     struct dif { 
      int secDif = time2.seconds2 - time1.seconds1; 
      int minDif = time2.minutes2 - time1.minutes1; 
      int hourDif = time2.hours2 - time1.hours1; 
     }; 

     printf("The difference is %d:%d:%d\n", hourDif, minDif, secDif); 
    } 



    int main(void) { 

     printf("Enter seconds1 (ss)\n"); 
     scanf("%d", &time1.seconds1); 

     printf("Enter minutes1 (mm)\n"); 
     scanf("%d", &time1.minutes1); 

     printf("Enter hours1 (hh)\n"); 
     scanf("%d", &time1.hours1); 

     printf("Enter seconds2 (ss)\n"); 
     scanf("%d", &time2.seconds2); 

     printf("Enter minutes2 (mm)\n"); 
     scanf("%d", &time2.minutes2); 

     printf("Enter hours2 (hh)\n"); 
     scanf("%d", &time2.hours2); 

     timeDif(time1, time2); 

    return 0; 
} 

Answer 1

在这个函数定义

int timeDif(time1, time2) { 
    struct dif { 
     int secDif = time2.seconds2 - time1.seconds1; 
     int minDif = time2.minutes2 - time1.minutes1; 
     int hourDif = time2.hours2 - time1.hours1; 
    }; 

    printf("The difference is %d:%d:%d\n", hourDif, minDif, secDif); 
} 

编译consideres标识符时间1和时间2的对象的名称。但是他们没有定义，因为你没有指定他们的类型。我认为你忘了指定对象的名称并只指定它们的类型。该函数的声明可能看起来像

int timeDif(struct time1 t1, struct time2 t2); 

考虑到，你必须使用结构变量与结构类型对象的声明结构名称帐户。

此函数虽然返回类型为int，但什么也不返回。它没有任何意义。你可能不会在C.

的定义中初始化结构的数据成员因此，这个结构定义

struct dif { 
     int secDif = time2.seconds2 - time1.seconds1; 
     int minDif = time2.minutes2 - time1.minutes1; 
     int hourDif = time2.hours2 - time1.hours1; 
    }; 

是无效的。与函数调用

timeDif(time1, time2); 

存在同样的问题我想你指的是以下

#include <stdio.h> 

struct time 
{ 
    int seconds; 
    int minutes; 
    int hours; 
}; 


struct time_dif 
{ 
    int secDif; 
    int minDif; 
    int hourDif; 
}; 

struct time_dif timeDif(struct time t1, struct time t2) 
{ 
    struct time_dif dif = 
    { 
     t2.seconds - t1.seconds, 
     t2.minutes - t1.minutes, 
     t2.hours - t1.hours 
    }; 

    return dif; 
} 



int main(void) 
{ 
    struct time t1, t2; 

    printf("Enter hours1 (hh): "); 
    scanf("%d", &t1.hours); 

    printf("Enter minutes1 (mm): "); 
    scanf("%d", &t1.minutes); 

    printf("Enter seconds1 (ss): "); 
    scanf("%d", &t1.seconds); 

    printf("Enter hours2 (hh): "); 
    scanf("%d", &t2.hours); 

    printf("Enter minutes2 (mm): "); 
    scanf("%d", &t2.minutes); 

    printf("Enter seconds2 (ss): "); 
    scanf("%d", &t2.seconds); 


    struct time_dif dif = timeDif(t1, t2); 

    printf("The difference is %d:%d:%d\n", dif.hourDif, dif.minDif, dif.secDif); 

    return 0; 
} 

要考虑到例如分钟的差别可以是负值。你应该改写功能timeDid这样的方式，它会提供两次正确的差异。

Answer 2

你的代码有一堆错误。我在你的代码中做了一些修改。

#include <stdio.h> 

struct time1 { 
    int seconds1; 
    int minutes1; 
    int hours1; 
}; 

struct time2 { 
    int seconds2; 
    int minutes2; 
    int hours2; 
}; 

int timeDif(struct time1 time1, struct time2 time2) { 
    int secDif = time2.seconds2 - time1.seconds1; 
    int minDif = time2.minutes2 - time1.minutes1; 
    int hourDif = time2.hours2 - time1.hours1; 

    printf("The difference is %d:%d:%d\n", hourDif, minDif, secDif); 
} 

int main(void) { 
    //declare the variable to use. 
    struct time1 time1; 
    struct time2 time2; 
    printf("Enter seconds1 (ss)\n"); 
    scanf("%d", &time1.seconds1); 

    printf("Enter minutes1 (mm)\n"); 
    scanf("%d", &time1.minutes1); 

    printf("Enter hours1 (hh)\n"); 
    scanf("%d", &time1.hours1); 

    printf("Enter seconds2 (ss)\n"); 
    scanf("%d", &time2.seconds2); 

    printf("Enter minutes2 (mm)\n"); 
    scanf("%d", &time2.minutes2); 

    printf("Enter hours2 (hh)\n"); 
    scanf("%d", &time2.hours2); 

    timeDif(time1, time2); 

    return 0; 
} 

Answer 3

每当你指的是任何struct或class，你必须创建objects。您不能直接使用它们，例如scanf("%d", &time1.seconds1);。相反，首先创建一个对象time1，然后使用该对象。这是非常简单的：

struct time1 t1; // creates an object t1 of the type time1. 
scanf("%d",&t1.seconds1); 

的主要原因是：当你定义一个struct，你实际上是定义一个type，就像一个int或char数据类型。你永远不会直接使用它们，如scanf("%d",&int);。您总是创建一个类型为int的变量，然后再使用它。同样，您为struct创建objects，然后再使用它们。

另外，函数timeDif的问题很少，例如它没有返回任何值。由于您的函数似乎并不需要在返回任何结果后才返回任何内容，因此请将其声明为void。另外，你没有理由在这个函数内部有struct，因为你在同一个函数中打印结果，并且没有在任何地方使用这个结构，而且这个结构也很容易出错。

这里是你的代码的修改后的版本：http://ideone.com/uzBnVS

Answer 4

你不需要定义三个结构，因为它们是同一类型 - 时间。你只能定义一个结构time：

#include <stdio.h> 

struct time { 
    int seconds; 
    int minutes; 
    int hours; 
}; 

void timeDif(struct time time1,struct time time2) { 
    struct time diff= { 
     time2.seconds - time1.seconds, 
     time2.minutes - time1.minutes, 
     time2.hours - time1.hours 
    }; 

    printf("The difference is %d:%d:%d\n", diff.hours, diff.minutes, diff.seconds); 
} 

int main(void) { 
    struct time time1,time2,diff; 
    printf("Enter seconds1 (ss)\n"); 
    scanf("%d", &time1.seconds); 

    printf("Enter minutes1 (mm)\n"); 
    scanf("%d", &time1.minutes); 

    printf("Enter hours1 (hh)\n"); 
    scanf("%d", &time1.hours); 

    printf("Enter seconds2 (ss)\n"); 
    scanf("%d", &time2.seconds); 

    printf("Enter minutes2 (mm)\n"); 
    scanf("%d", &time2.minutes); 

    printf("Enter hours2 (hh)\n"); 
    scanf("%d", &time2.hours); 

    timeDif(time1, time2); 

    return 0; 
}