Using file from command line

[Crakrjack]

I'm trying to read in a file specified in the command line but I'm having some trouble. The command line entry specifies the inputfile preceded by '<' and the output file preceded by '>' like so

./program -v < input_file.cmd > output_file.cmd

This is what I've got so far.

int main(int argc,char* argv[])
{


string strv="-v";
string input="<";
string output=">";
string str;
string input_file;
const char* in=input_file.c_str();
string output_file;
const char* out=output_file.c_str();
bool verbose=false;
int i;
//deal with command line paramaters
for (i=0;i<argc;i++)
{
cout<<"argc="<<argc<<" and argv at "<<i<<" is "<<argv[i]<<endl;
	if (argv[i]==strv)
	verbose=true;
	else if (argv[i]==input)
	input_file=argv[i+1];
	else if (argv[i]==output)
	output_file=argv[i+1];
	else	// nop
	;
}


ifstream fin(in,ifstream::in);	

This compiles ok, but when i run it using
./program -v < test1.cmd
I get a segfault, if i cout argc it returns '2' where i would expect for this command line entry, I 'd get 4.

I'm not yet outputting to file, just to the screen so im not specifying an output file yet.
If anyone could help on this it'd be much appreciated.

[vlad from moscow]

The value of variable in is an address of an empty character array that (the address) becames invalid after assigning a new value to input_file. You should remove declarations of in and out and use

ifstream fin(input_file.c_str() ifstream::in);

instead of

ifstream fin(in,ifstream::in);

[Crakrjack]

Thanks for that, however argc is still taking a value of 2 when there should be 4??
I've found now that if i change string input="in"
and pass
./program -v in test1.cmd
to the command line it works fine however the spec for my assignment requires the < before the filename?
I'm using cygwin so im not sure if my issue is specific to that or if < has some special meaning as this and anything beyond it is not being read into argv[].

[vlad from moscow]

Symbols < and > has special meaning in the command line. Symbol < means that the standard input stream will be read from a file with the name following <. Symbol > means that standard output stream will be redirected in a file with the name following >. So the command line processor processes this symbol before passing the command line parameters to a calling program.

[Crakrjack]

ok, things are starting to make sense now, so what parameter do i enter when i create my input stream?

ifstream fin(????????,ifstream::in);

[vlad from moscow]

Use the command line without symbols < and >

program -v input_file.cmd output_file.cmd

[Crakrjack]

The assignment spec requires the use of the symbols, my code will be run automatically by the lecturers marking script.

[vlad from moscow]

I am not sure bur try to use them without spaces between them and the filename.

[Crakrjack]

Thanks for your help people, I've got it sorted now.

Turns out i don't need to create a filestream, i just use getline(cin,string) and it reads from the specified file.