Reading from a file in Xcode/using cin

Tom_Arch · 06-22-2009, 12:40 AM

Hey all,

In Xcode, do you have to put the text file somewhere special for it to be read? My file opening code runs but is always .fail().

Also how can I make an ifstream from cin?

Thanks for any help

CodeMonkey · 06-22-2009, 01:30 AM

I don't know about Xcode. Check to see where the executable file is being placed. Some (most) IDEs run the compiled program in a different environment than that in which the executable file is, but if you can find the file, you can run it wherever you like.

As for your second question, you can't make an ifstream from cin because ifstream is derived from istream, which is what cin is. I think it is more likely that you mean something else entirely, so please restate your question.

Tom_Arch · 06-22-2009, 04:36 PM

Well if there is no file specified in argv[] I want to read from std input instead. How can that be implemented?

matsp · 06-22-2009, 04:38 PM

Exactly what is your command that you run?

--
Mats

Tom_Arch · 06-22-2009, 10:38 PM

Ok the program is a search program which searches a file for the first command argument, then prints out any line with that in it. If there's only one argument, it uses cin.

salami testdata.txt

is the argument line I'm trying to do now, and I've no idea how I would implement it if it was only

salami

thanks for looking

**Salem** · 06-22-2009, 11:03 PM

Code:

void myInputFunction ( ifstream &in );

int main ( int argc, char *argv ) {
  if ( argc < 2 ) {
    myInputFunction( cin );
  } else {
    ifstream myfile(argv[1]);
    myInputFunction( myfile );
  }
}

Use a function which takes a reference to an ifstream, then choose where that ifstream comes from.

Sebastiani · 06-22-2009, 11:12 PM

Also, you can use istream::read(char*, size_t) and get the length of the read from istream::gcount( ).

Tom_Arch · 06-23-2009, 02:21 AM

Alright so cin is a reference to an ifstream? Would I have to open the file before I pass it to myInputFunction? because if the open command was in myInputFunction, would that work with cin?

Sebastiani · 06-23-2009, 04:49 AM

>> Alright so cin is a reference to an ifstream?

I didn't spot that earlier, but no, cin is actually an instance of an object that is derived from an istream (not ifstream).

>> Would I have to open the file before I pass it to myInputFunction?

Yes. Just be sure to change the parameter to a reference to an istream, of course.

>> because if the open command was in myInputFunction, would that work with cin?

Nope.

06-22-2009, 12:40 AM	#1
Tom_Arch Registered User Join Date: Apr 2009 Posts: 24	Reading from a file in Xcode/using cin Hey all, In Xcode, do you have to put the text file somewhere special for it to be read? My file opening code runs but is always .fail(). Also how can I make an ifstream from cin? Thanks for any help
Tom_Arch is offline

06-22-2009, 01:30 AM	#2
CodeMonkey Kiss the monkey. Join Date: Sep 2001 Posts: 810	I don't know about Xcode. Check to see where the executable file is being placed. Some (most) IDEs run the compiled program in a different environment than that in which the executable file is, but if you can find the file, you can run it wherever you like. As for your second question, you can't make an ifstream from cin because ifstream is derived from istream, which is what cin is. I think it is more likely that you mean something else entirely, so please restate your question. __________________ "If you tell the truth, you don't have to remember anything" -Mark Twain
CodeMonkey is offline

06-22-2009, 04:36 PM	#3
Tom_Arch Registered User Join Date: Apr 2009 Posts: 24	Well if there is no file specified in argv[] I want to read from std input instead. How can that be implemented?
Tom_Arch is offline

06-22-2009, 04:38 PM	#4
matsp Kernel hacker Join Date: Jul 2007 Location: Farncombe, Surrey, England Posts: 15,686	Exactly what is your command that you run? -- Mats __________________ Compilers can produce warnings - make the compiler programmers happy: Use them! Please don't PM me for help - and no, I don't do help over instant messengers.
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06-22-2009, 10:38 PM	#5
Tom_Arch Registered User Join Date: Apr 2009 Posts: 24	Ok the program is a search program which searches a file for the first command argument, then prints out any line with that in it. If there's only one argument, it uses cin. salami testdata.txt is the argument line I'm trying to do now, and I've no idea how I would implement it if it was only salami thanks for looking
Tom_Arch is offline

06-22-2009, 11:03 PM	#6
Salem and the hat of vanishing Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,214	Code: void myInputFunction ( ifstream &in ); int main ( int argc, char *argv ) { if ( argc < 2 ) { myInputFunction( cin ); } else { ifstream myfile(argv[1]); myInputFunction( myfile ); } } Use a function which takes a reference to an ifstream, then choose where that ifstream comes from. __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut. Up to 8Mb PlusNet broadband from only £5.99 a month!
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06-22-2009, 11:12 PM	#7
Sebastiani Guest Join Date: Aug 2001 Posts: 4,923	Also, you can use istream::read(char*, size_t) and get the length of the read from istream::gcount( ).
Sebastiani is offline

06-23-2009, 02:21 AM	#8
Tom_Arch Registered User Join Date: Apr 2009 Posts: 24	Alright so cin is a reference to an ifstream? Would I have to open the file before I pass it to myInputFunction? because if the open command was in myInputFunction, would that work with cin?
Tom_Arch is offline

06-23-2009, 04:49 AM	#9
Sebastiani Guest Join Date: Aug 2001 Posts: 4,923	>> Alright so cin is a reference to an ifstream? I didn't spot that earlier, but no, cin is actually an instance of an object that is derived from an istream (not ifstream). >> Would I have to open the file before I pass it to myInputFunction? Yes. Just be sure to change the parameter to a reference to an istream, of course. >> because if the open command was in myInputFunction, would that work with cin? Nope.
Sebastiani is offline

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