Question regarding fopen( ) function

[Alien]

Hi,

I have a question regarding the fopen( ) function. I wrote this piece of code:

 
#include <stdio.h>
 
int main()
{
   FILE *fp;
   char file[] = "data.txt";
   fp = fopen(file, "r");
 
   if(fp == NULL)
       printf("failure\n");
   else
      printf("Success\n");
 
}
 
 

When I run this program, I only get success when data.txt is in the same directory I am working in (writing out this source code). If I move out the data.txt into another directory, I get failure.

Is this normal to happen or is there another way to read use fopen( ) to open text files in another directory.

Regards.

Alien

[Banfa]

Is this normal to happen or is there another way to read use fopen( ) to open text files in another directory.

This is normal, to open a file you have to tell the system where to look. It defaults to the current working directory which from an IDE is the directory that the exe exists in and from a command prompt is the directory it is showing as the current directory.

If you want to open a file located elsewhere you will need to use an absolute or relative path to the file.

[Alien]

This is normal, to open a file you have to tell the system where to look. It defaults to the current working directory which from an IDE is the directory that the exe exists in and from a command prompt is the directory it is showing as the current directory.

If you want to open a file located elsewhere you will need to use an absolute or relative path to the file.

You mean something like this?

FILE *fp = "/home/mydirectory/data.txt";
 
fopen(fp, "r");
 
 

[mohaakilla51]

yes,or like this:

FILE *fp = "C:\Crazy\random\directory\that\is\absolute\data.txt";
 
fopen(fp, "r");
 

[Banfa]

You mean something like this?

FILE *fp = "/home/mydirectory/data.txt";
 
fopen(fp, "r");
 
 

no more like this

char filename[] = "/home/mydirectory/data.txt";
FILE *fp;
 
fp = fopen(filename, "r");
 

[weaknessforcats]

yes,or like this:

Code: ( text )
FILE *fp = "C:\Crazy\rando m\directory\tha t\is\absolute\d ata.tx t";

fopen(fp, "r");

Actually, you meant to say:

yes,or like this:
 
Code: ( text )
FILE *fp = "C:\\Crazy\\random\\directory\\that\\is\\absolute\\data.txt";
 
fopen(fp, "r");
 

Remember, the \ is an escape sequence and not a character.

[mohaakilla51]

woops... I knew that all along, I was Just testing you... yeah... that's it...

[earth]

This is normal, to open a file you have to tell the system where to look. It defaults to the current working directory which from an IDE is the directory that the exe exists in and from a command prompt is the directory it is showing as the current directory.

If you want to open a file located elsewhere you will need to use an absolute or relative path to the file.

From the beginning i thought that "current working directory" means the courrent directory of the "exe" file! But now i realize it is not true!!!
for example: the code in Alien's first post. suppose the .exe file and the data.txt file are in "c:\xyz" folder.
If i run the exe in this way: C:\xyz>Alien.exe it works ok.(here command prompt current directory is c:\xyz)
but if i try to run it in this way: C:\>xyz\Alien.exe it does not work!!(here command prompt current directory is c:\, but the exe and the txt file are in same directory)
Now this is not that problem if someone is working in command prompt (one can simply go to that directory....). But it is really a problem when I want to run that Alien.exe file from another code using system("xyz\\Al ien.exe"); or system("c:\\xyz \\Alien.exe"); command. It does not work!! when the Alien.exe runs it does not looks for the data.txt file in C:\xyz folder instead it looks for the current directory where the main exe (in which i m calling the system command) is!
Here my question is : is there anything i can do in the main code so that when i call the system(); command and run Alien.exe, The Alien.exe will get C:\xyz as its current working directory?

[Banfa]

The only really platform independent way to achieve this is to pass the directory of the input file (or its entire path) on the command line of the program

instead of calling

C:\>\xyz\progra m.exe

and program.exe assuming that text.txt is in the current working directory you call it like this

C:\>\xyz\progra m.exe C:\xyz\

or

C:\>\xyz\progra m.exe C:\xyz\text.txt

and program.exe uses the information provided to open text.txt from the correct location.

Alternitively you could temporarily change the current working directory of the calling program but I don't think this is a good idea.


If you are happy to use non-portable code then it rather depends on your platform. For instance on Windows you can call GetModuleFileNa me to retrieve the full path of the exe from which you could construct the path to text.txt.