File I/O with arrays

**20,000leeks** · 09-17-2006

Yet another newbie-ish problem.... this time slightly more advanced.

I'm having a bit of trouble reading information as text from a file.... The information involves three different sets of integers, two normal, and one an array, like so:

Code:

100
30
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111131111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111131111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111222222221111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111131111111111111111111111111222222221111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111131111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111113111111111111111111111111
1111111111111111113111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111311111111111111111111111111111111111111111111111111
1111111111111111111111111111131111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111311111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

Yes, it's a lot, but I'm trying to hard-code something for testing.

My file I/O operation currently reads like so:-

Code:

int location::fileread(char filename[10])
{
    ifstream a_file ( filename );
    if ( !a_file.is_open() ) {
    cout<<"File could not be opened./n";
    return 0;
      }
else {
    a_file>>mapx;                              //read the first value, the x-value
    a_file>>mapy;                              //read the second value, the y-value
    a_file>>terrain[mapx][mapy];      //store the long section of 1s, 2s, and 3s in terrain[100][30]
    return 1;}
}

This results in me getting a blank screen with no information whatsoever. I don't know if this means that the x and y values are being read but the array isn't, or if the whole lot is horribly wrong (the results would, I think, be pretty much the same). I'm pretty sure the problem lies in the array. Does instreaming read a single character? Multiple characters? The entire line? Is there any way to alter this?

It's probably a really stupid question, but any help would be greatly appreciated!

**bumfluff** · 09-17-2006

Erm, why are you returning 1 after the else statement as that means that there is an error. Return 1 if the file can't be opened.

**Salem** · 09-17-2006

> a_file>>terrain[mapx][mapy]
This refers to the element just off the end of the array

Maybe

Code:

for ( int r = 0 ; r < mapy ; r++ ) {
  for ( int c = 0 ; c < mapx ; c++ ) {
    a_file>>terrain[r][c];
  }
}

**20,000leeks** · 09-17-2006

To be honest, I just prefer it that way.... the main() setup goes something like so:

Code:

int main()
{
    char mapf[10];
    cout<<"Enter map file:\n";
    cin>>mapf;
    if (locate.fileread(mapf) == 1){
    clrscr();
    charx = mapx/2;
    chary = mapy/2;
    mapprint(mapx, mapy);
    do {
        input();
        }
        while (input() != 0) ;
        clrscr();
        }
        else {
    cursorpos(0,0);
    cout<<"Goodbye!";}
}

I just have a thing about 1 being 'true' and 0 being 'false'. It's not that much trouble to change, though, if you think I should.

**20,000leeks** · 09-17-2006

Hmm, thanks for the advice Salem, but it's still not loading correctly

. Maybe I should figure out how the C commands work rather than mess around with the C++ commands... although the C version seems so much more complex.

EDIT:
I've figured out how to manage it, rather than storing each variable in a two dimensional way in the file itself, I have to store it one on top of the other (like
1
1
1
1
1
1
1
etc...) and then read it like that. Unless there's some way to integrate strings and integers.... anyway, for the time being, problem solved.

**Prelude** · 09-17-2006

>Maybe

Code:

for ( int r = 0 ; r < mapy ; r++ ) {
  for ( int c = 0 ; c < mapx ; c++ ) {
    a_file>>terrain[r][c];
  }
}

Maybe not. It looks like all of the digits are intended to be unique entities but they're not separated by whitespace. a_file>>terrain[r][c] is unlikely to work as expected in this situation. Something more like this would work if I'm judging the file properly:

Code:

a_file>> first;
a_file>> second >> ws;

for ( int i = 0; i < mapy; i++ ) {
  for ( int j = 0; j < mapx; j++ )
    terrain[i][j] = a_file.get() - '0';
}

**20,000leeks** · 09-17-2006

Hmm, it *almost* works. I think because there's a white space on the end of each line, that makes things a little more complex, so I tried:

Code:

for ( int i = 0; i < mapy; i++ ) {
       for ( int j = 0; j < mapx; j++ )
        if ( j < mapx){
        terrain[j][i] = a_file.get() - '0';
        }
        else a_file>> terrain [j][i];
       }

but it still comes out on a slant (like this

Code:

 .................................................
. ................................................
.. ...............................................
... ..............................................
.... .............................................
..... ............................................
...... ...........................................
....... ..........................................

**dwks** · 09-17-2006

You need to read in the '\n', I think.

**Prelude** · 09-17-2006

Ah, so there are linebreaks in the file itself. Okay, how about this:

Code:

for ( int i = 0; i < mapy; i++ ) {
  for ( int j = 0; j < mapx; j++ ) {
    char ch;

    if ( !a_file.get ( ch ) ) {
      // Handle an input error
    }

    if ( ch != '\n' )
      terrain[i][j] = ch - '0';
  }
}

**dwks** · 09-17-2006

You could just do this:

Code:

for ( int i = 0; i < mapy; i++ ) {
  for ( int j = 0; j < mapx; j++ )
    terrain[i][j] = a_file.get() - '0';

  while(a_file.get() != '\n' && !a_file.bad());
}

.bad() might not be the best function to use however.

**20,000leeks** · 09-17-2006

Hmm, I tried

Code:

for ( int i = 0; i < mapy; i++ ) {
       for ( int j = 0; j < mapx; j++ )
       if (a_file.get()!='\n'){
        terrain[j][i] = a_file.get() - '0';
        }
        else
        {j = mapx;
        }

but that seemed to cut out parts of the file.

Code:

for ( int i = 0; i < mapy; i++ ) {
  for ( int j = 0; j < mapx; j++ )
    terrain[i][j] = a_file.get() - '0';

  while(a_file.get() != '\n' && !a_file.bad());
}

didn't load the map at all for some reason :S

**Prelude** · 09-17-2006

>You could just do this:
Handling the linebreak outside of the inner loop is definitely a better solution, but I'd still want some error checking:

Code:

for ( int i = 0; i < mapy; i++ ) {
  for ( int j = 0; j < mapx; j++ ) {
    char ch;

    if ( !a_file.get ( ch ) ) {
      // Handle an input error
    }

    terrain[i][j] = ch - '0';
  }

  a_file.ignore();
}

**20,000leeks** · 09-17-2006

Aha! Problem solved! Thanks a lot, I'd probably have resorted to using a single-column file otherwise....

**dwks** · 09-17-2006

I forgot about ignore() . . .

I'm sure you've fixed this by now, but here's an earlier line you posted:

Code:

cout<<"File could not be opened./n";

**20,000leeks** · 09-17-2006

Ah, yes, I noticed that one about five minutes after posting it.... I guess there's an upside to uncomplicated applications, you catch typos faster.

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