Intializing the method's parameter list

[seforo]

Hi Guys,

What is the advantage of intializing the parameter list of the method, e.g
[CODE=c++]
class ReadFile
{
ReadFile(const char* filename = "Mystuff.tx t")
{
// Function defination goes here
}
// Define the rest of the class here
}
[/CODE]

I am asking this because having that I still have to pass the file name when I instantiate the object of the class ReadFile, otherwise I get an error. However I have seen many people defining their classes like this.

[ilikepython]

Hi Guys,

What is the advantage of intializing the parameter list of the method, e.g
[CODE=cpp]
class ReadFile
{
ReadFile(const char* filename = "Mystuff.tx t")
{
// Function defination goes here
}
// Define the rest of the class here
}
[/CODE]

I am asking this because having that I still have to pass the file name when I instantiate the object of the class ReadFile, otherwise I get an error. However I have seen many people defining their classes like this.

That is a default arguement. If you don't pass it, it defaults to the one you gave it in the declaration or prototype. I think yours doesn't work is because you need something like this:
[code=cpp]
class ReadFile
{
ReadFile(const char filename[20] = "Mystuff.tx t");
}

ReadFile::ReadF ile(const char filename[20])
{
// you dont have to pass the filename
}
[/code]
The default has to be in the declaration.

[weaknessforcats]

I think yours doesn't work is because you need something like this:

It should work fine. The argument is a const char* and a literal is a const. The onlt difference is that the function cannot use the file name in a non-const manner.

[seforo]

Let me be specific; The following piece of code does not compile:
[CODE=cpp]
#include <iostream>
using namespace std;
class Test
{
public:
Test(char * file = "galice.roo t");
void Show()
{
}
};

Test::Test(char * file)
{
}

int main()
{
Test teko();
teko.Show();
return 0;
}
[/CODE]
Unless I pass the file name galice.root as an arguement to the object of the class Test that I instatiated, I always get the error message:
request for member `Show' in `teko()', which is of non-aggregate type `Test ()()'

[ilikepython]

Let me be specific; The following piece of code does not compile:
[CODE=cpp]
#include <iostream>
using namespace std;
class Test
{
public:
Test(char * file = "galice.roo t");
void Show()
{
}
};

Test::Test(char * file)
{
}

int main()
{
Test teko();
teko.Show();
return 0;
}
[/CODE]
Unless I pass the file name galice.root as an arguement to the object of the class Test that I instatiated, I always get the error message:
request for member `Show' in `teko()', which is of non-aggregate type `Test ()()'

You need to leave off the parenthesis when creating the object with no arguements.

[seforo]

You need to leave off the parenthesis when creating the object with no arguements.

Thank you, it works now