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file reading from variables

Started by Shenjoku Jan 29, 2007 at 9:34 PM 8 replies 750+ views
Original Post
Shenjoku
Shenjoku
in order to access a library of data I need to read information from specific files, but I need it to read the file pathname based on a variable. for example: char Name; //holds the filename to be gathered from the program somewhere then I need to read a pathname like this: "..\\data\\Name.file" I have no idea how to get it to input what's in the variable in that place so I'm coming to anyone here for help :)
AdamGL
AdamGL
First off, you must specify what language you are programming in. In general, opening files is done by calling a function which handles most of the opening for you. You must simply supply it with the location, and the read/write type of the file. You wanted to insert the value of the variable as the pathname to your file? No problem. Below is C++ code:
#include <iostream>#include <fstream>using namespace std;int main () {  char Name = "place/somewhere/hi.txt";  ifstream fin;  //declare   fin.open (Name, ifstream::in);//opens the file at the location specified by Name  //do stuff with data here  fin.close();}


Hope that helps. Further help can be given if we know what language you are programming in.
bi-FreeSoftware
jflanglois
jflanglois
Quote:
Original post by AdamGL
First off, you must specify what language you are programming in. In general, opening files is done by calling a function which handles most of the opening for you. You must simply supply it with the location, and the read/write type of the file. You wanted to insert the value of the variable as the pathname to your file? No problem. Below is C++ code:
*** Source Snippet Removed ***

Hope that helps. Further help can be given if we know what language you are programming in.


Quickly! Before anyone sees! Use std::string instead of char. Or if you must, char const []. (hint: your code will not compile)

OP: Indeed, we need to know the programming language and perhaps even some more details about the problem. What have you tried that doesn't work?


jfl.
Shenjoku
Shenjoku
ok let me be more clear. I'm using c++ they are char[32] variables used to store a players name for their data file so when loaded it will read the file path as
"..\\Data\\PlayersName.dat" so I need to somehow slap the char[32] where "PlayersName" is.
KulSeran
KulSeran
Are you trying to do this?

std::string Name;cin >> Name;string path = "..\\data\\" + Name + ".file";fstream myfile ( path.c_str(), ios::in );


Or

std::string Name;cin >> Name;fstream myfile ( Name.c_str(), ios::in );string path;getline ( path, myfile, "\n" );string path2;copy ( path.find_first_of( "\"" ), path.find_last_of ("\""), path2 );



sorry, but your statement is still kinda unclear as to what you are looking to do.
jouley
jouley
Quote:
Original post by Shenjoku
ok let me be more clear. I'm using c++ they are char[32] variables

Don't use char[]s (or even char*s) if you're using C++. Instead, use std::strings. They're much easier, as you'll see.
Quote:
used to store a players name for their data file so when loaded it will read the file path as
"..\\Data\\PlayersName.dat" so I need to somehow slap the char[32] std::string where "PlayersName" is.

Consider the following, that does exactly what you want:
#include <string>#include <iostream>int main( ){	std::string strPath = "../Data/PlayersName.dat";	const std::string strToReplace = "PlayersName";	std::string strPlayerName = "jouley";	strPath.replace(strPath.find(strToReplace, 0), strToReplace.size( ), strPlayerName);	std::cout << strPath << std::endl;	return 0;}

The one long line could have been broken up into smaller ones, but you'd be hard pressed to do anything so easily without a String library with the capabilities of std::string.

Hooray for std::strings! Boo for chars!
-jouley

[Edit: Pretty much what KulSeran said, just another approach.]
Zakwayda
Zakwayda
Quote:
Original post by Shenjoku
ok let me be more clear. I'm using c++ they are char[32] variables used to store a players name for their data file so when loaded it will read the file path as
"..\\Data\\PlayersName.dat" so I need to somehow slap the char[32] where "PlayersName" is.
In C++ you would use std::string, along with std::ifstream as demonstrated in AdamGL's code. A very simple example:

std::string path = ".../Data/";path += player_name; // player_name could be a std::string, or a null-terminated C-style stringpath += ".dat";std::ifstream file(path.c_str());assert(file); // More sophisticated error checking goes here...// Do stuff with file...// File is closed automatically when 'file' goes out of scope

Does that answer your question?

[Edit: So very slow...]
Shenjoku
Shenjoku
see I would be using string except for some reason my compiler decided that no matter, string header file or not, it won't read string as a type of storage class. I have no idea why. I include the header file and everything but it still says string doesn't exist when I try to use it. hence all the chars.
jouley
jouley
Quote:
Original post by Shenjoku
see I would be using string except for some reason my compiler decided that no matter, string header file or not, it won't read string as a type of storage class. I have no idea why. I include the header file and everything but it still says string doesn't exist when I try to use it. hence all the chars.

What compiler, and what are the errors?
rip-off
rip-off
Quote:
Original post by Shenjoku
see I would be using string except for some reason my compiler decided that no matter, string header file or not, it won't read string as a type of storage class. I have no idea why. I include the header file and everything but it still says string doesn't exist when I try to use it. hence all the chars.


Are you *sure* the compiler knows you are using C++ (hint: some compilers will base the language off the file extension, .c vs .cpp )

Are you #include'ing (and not string.h)

Are you typing std::string?

Ths code should work on all valid c++ compilers:
// source.cpp#include <string>int main(){    std::string str;}


If that doesn't work on your compiler, post

1) compiler name
2) the errors (hint: if you ever have a programming problem, post the errors)
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