Open file with fopen function

[EricKantana]

Hi, i really want to know how i can open file using fopen function while i am not sure where the txt file located. I mean, if i make a simple program and then i want to share it with my friend, how i can tell the program to open the txt file while i don't know where the txt file is located?

--> The exe is located in a some folder and the txt is located in the sub folder

[codewalker]

You cant do that.
You will have to specify full or relative path to fopen
Something like "/usr/home/filename.txt or "dir/filename.txt"

[coder777]

You can use e.g. cin/cout to ask the user for the path and file name.

[Duthomhas]

Three simple ways:

1. Have the user specify the filename when starting your program. 
This is how many, many applications work.
Drag and drop the file onto the exe and it'll work.

int main( int argc, char** argv )
{
  FILE* f = NULL;

  if (argc != 2)
  {
    printf( "usage: %s FILENAME\n", argv[0] );
    return 1;
  }

  f = fopen( argv[1], "r" );
  if (!f) ...

  ...

  fclose( f );
  return 0;
}

2. Pipe the file into standard input. 
Many Unix utilities work this way.

int main()
{
  // use stdin
}

C:\Users\Eric\prog> a.exe < filename.txt

% ./a.out < filename.txt

3. Ask the user for it. 
This method is pure disadvantage; user must know how to enter filename without being able to use tab-completion or any other helps to find it.

int main()
{
  FILE* f = NULL;

  char filename[ 1024 ] = { 0 };
  printf( "file? " );
  fflush( stdout );
  if (!fgets( filename, 1024, stdin ) || filename[1023])
  {
    fprintf( stderr, "bad filename!\n" );
    return 1;
  }

  f = fopen( filename, "r" );
  if (!f) ...

  ...

  fclose( f );
  return 0;
}

Hope this helps.

[EricKantana]

Hi guys, thanks for the solutions. But i had solve this.
I just need write the directory path like this
"FILE* file;"
"file=fopen(".\\subfolder\\text.txt","r");"

Before, i tested to write like this "file=fopen("text.txt","r");" and its work
i don't know for sure, but i think it tells the program to find this file in same directory as the exe file located

so i just googling around and found out about how to access the subdirectory. it just need a dot before the backslash

Thanks guy

[Duthomhas]

Anything that starts with a slash is an absolute path.
Anything that doesn't is a relative path.

\foo\bar is an absolute path.
foo\bar is a relative path.

(Note that the drive letter is a distinct issue on windows:
C:\foo\bar is absolute;
C:foo\bar is relative.)

Consequently, your program would work fine with just

FILE* file = fopen( "subfolder\\text.txt", "r" );  // relative path 

Hope this helps.

[EricKantana]

Thanks Duoas, that is really helpfull.