multiple cpp files

[subramanian100in]

Suppose I have three files namely: 1.h, 1.cpp, 2.cpp

The following is 1.h
----------------------------
#ifndef _1_H
#define _1_H

class Test
{
public:
static std::string str;

void print(const std::string & x = str) { std::cout << x <<
std::endl; }
};

#endif

The following is 1.cpp
--------------------------------
#include <iostream>
#include <string>
#include "1.h"

using namespace std;

extern void fn();

int main()
{
cout << Test::str << endl;

Test obj;
obj.print();
fn();
obj.print();
return 0;
}

The following is 2.cpp
-------------------------------
#include <iostream>
#include <string>
#include "1.h"

using namespace std;

string Test::str = "static const string";

void fn()
{
Test::str = "static const reassigned";
return;
}

When I compile this program with
g++ -std=c++98 -pedantic -Wall -Wextra 1.cpp 2.cpp
it compiles fine. When it is run, the following output is produced.

static const string
static const string
static const reassigned

In 1.cpp, obj.print( ) is called. It is an inline function with
default argument. This default argument is the static data member
whose value is defined in 2.cpp

How does the compiler know the value of the default argument when it
compiles 1.cpp in order to do the inlining. But it prints the value
correctly. I do not understand.

Kindly explain

Thanks
V.Subramanian

 

[Ondra Holub]

Suppose I have three files namely: 1.h, 1.cpp, 2.cpp

The following is 1.h
----------------------------
#ifndef _1_H
#define _1_H

class Test
{
public:
static std::string str;

void print(const std::string & x = str) { std::cout << x <<
std::endl; }

};

#endif

The following is 1.cpp
--------------------------------
#include <iostream>
#include <string>
#include "1.h"

using namespace std;

extern void fn();

int main()
{
cout << Test::str << endl;

Test obj;
obj.print();
fn();
obj.print();
return 0;

}

The following is 2.cpp
-------------------------------
#include <iostream>
#include <string>
#include "1.h"

using namespace std;

string Test::str = "static const string";

void fn()
{
Test::str = "static const reassigned";
return;

}

When I compile this program with
g++ -std=c++98 -pedantic -Wall -Wextra 1.cpp 2.cpp
it compiles fine. When it is run, the following output is produced.

static const string
static const string
static const reassigned

In 1.cpp, obj.print( ) is called. It is an inline function with
default argument. This default argument is the static data member
whose value is defined in 2.cpp

How does the compiler know the value of the default argument when it
compiles 1.cpp in order to do the inlining. But it prints the value
correctly. I do not understand.

Compiler knows the default argument. It simply calls it same way as if
you write obj.print(Test::str). Since Test::str is declared in header
which was included, it is ok.

 

[subramanian100in]

Compiler knows the default argument. It simply calls it same way as if
you write obj.print(Test::str). Since Test::str is declared in header
which was included, it is ok.

Does it mean that the value of Test::str (which is defined in 2.cpp)
need not be known for doing the inline ?

Thanks
V.Subramanian