Thread: How to use int argc, char* argv[] ?

Hi,

I am not sure how to use int argc, char* argv[]. Anyone could tell me when should I use it?

Also, I cannot compile the following code. The error shows initialization of 'i' is skipped by 'default' label. What does it mean?

#include <iostream>

using namespace std;

int main(int argc, char* argv[])
{
switch(argc-1)
{
case 2:
case 3:
case 4:
for(int i = 1; i < argc; i++)
cout << "Argument " << i << " is " << argv[i] << endl;
break;
default:
cout << "You entered the incorrect number of arguments. " << endl
<< "Please enter 2, 3 or 4 arguments only. " << endl;
}
return 0;
}

Thanks in advance.

gogo

> I am not sure how to use int argc, char* argv[]. Anyone could tell me when should I use it?
Whenever you need to access parameters on the command line

Your program looks OK as it stands.

> The error shows initialization of 'i' is skipped by 'default' label.
It means you have an older C++ compiler

Originally, the declaration within the for loop meant this

Code:

int i;
for( i = 1; i < argc; i++)
    cout << "Argument " << i << " is " << argv[i] << endl;

The scope of i was from just before the for loop, to the end of the enclosing } (in this case, your switch statement).
Basically, you have a variable declared (i), which is not initialised in all cases.

A newer compiler declares things like so (in effect)

Code:

{ int i;
for( i = 1; i < argc; i++)
    cout << "Argument " << i << " is " << argv[i] << endl;
}

Now the scope of i is much less - certainly not the whole case statment.

The GNU compiler has a switch to turn this on and off
> gxx -fno-for-scope cpr-test.cpp
cpr-test.cpp: In function `int main(int, char **)':
cpr-test.cpp:17: jump to case label
cpr-test.cpp:14: crosses initialization of `int i'

> gxx cpr-test.cpp

Thanks for your kind help. May I ask you how should I compile it through VC++? I do not have any MS-Dos mode compiler.

Thanks

gogo

> May I ask you how should I compile it through VC++?
Like you already are, but without that warning?

Dunno - declare 'i' before you enter the switch statement, not when you declare the for loop.

Or perhaps

Code:

case 4: 
{ // spoof an extra scope 
     for(int i = 1; i < argc; i++)
     cout << "Argument " << i << " is " << argv[i] << endl;
}
break;

Compiler's broken - the rest is hackery