domiyanyue

#ifndef TIME_H
#define TIME_H
struct Time {
    int hour;
    int minute;
};

void printTime(Time t);

#endif

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#ifndef A_UNIQUE_HEADER_FILE_GUARD_NAME
#define A_UNIQUE_HEADER_FILE_GUARD_NAME

// header file content 
...

#endif

domiyanyue

struct Time{
  int hour;
  int minutes;
};

struct Time{
  int hour;
  int minutes;
};

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...
// replaced from first #include "time.h"
struct Time {
    int hour;
    int minute;
};
...
// replaced from #include "util.h" which also include "time.h"
struct Time {
    int hour;

domiyanyue

$ g++ -c main.cpp  
In file included from util.h:1:0,
                 from main.cpp:3:
time.h:1:8: error: redefinition of ‘struct Time’
 struct Time {
        ^~~~
In file included from main.cpp:2:0:
time.h:1:8: note: previous definition of ‘struct Time’
 struct Time {
        ^~~~

domiyanyue

#include <iostream>
#include "time.h"
#include "util.h"

int main(){
    Time t;
    t.hour = 2;
    t.minute = 10;
    printTime(t);
    std::cout << "is Day time? " << isDayTime(t) << std::endl;

domiyanyue

#include "time.h"

bool isDayTime(Time d);

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struct Time {
    int hour;
    int minute;
};

void printTime(Time t);

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struct Point {
    int x;
    int y;
};

enum Color { black = 0, white = 1, grey = 2};

Point p;
Color c = Color::black;

domiyanyue

#include "util.h"

int main(){
    // set to 9:10
    Time t(9, 10);
    return isDayTime(t);
}