Reading in an array of text from a file?

Well, I've got single lines down, so I'm not a total failure here. However, I'm trying to read a 10x10 array of characters from a textfile into a 10x10 array of characters in a... char map[10][10].

Someone suggested using getline, 10 times, in a loop.

Code:

---

int main()
{
    ifstream mapFile;
    mapFile.open("map/map01.txt");           
    mapFile.getline(&map[0][0],10);
    mapFile.close();
    cout << map[1][1];
    int hi;
    cin >> hi;
    return 0;
}

---

So, when the 10xtimes in a loop thing failed, I took the loop bit out and just tried reading in the first line of text.

Now, my understanding of the syntax is this: getline reads from mapFile, and puts the text into map, starting at *map[0][0], and reads in for... 10 characters in the text file. From my understanding, this should put the first line of the text file into positions [0][0] to [10][0] in char map.

Obviously my understanding is wrong, because I'm making this post. More specifically, I get blank output from cout << map[1][1]. Which, from my understanding, should display the character in the array at position [1][1]. I tested this by include map[1][1] = 'a' right above the cout bit.

Er, yes, so I guess I'm wondering what I need to plug into getline to... get it properly reading my lines, or if that's the entirely wrong approach.

what's wrong with reading it in character-by-character?

did nested for loops go out of syle or something?

Well, on the subject of reading it in character by character, I'm... not really sure how to do that either. I know it involves nested for loops with increasing x and y values for a char[x][y] sort of set up, but I'm not sure how to get x and y there to point at proper points in the loaded file.

Call mapFile.getline(map[0],10), since map[0] is a character array just like if you had a single character array that you were using with getline. If you put that call in a loop, then you would use map[i], basically looping through each character array in the map array.

You should look into using the C++ string class instead of character arrays, though. Also, the C++ vector class is a better idea than a plain C style array.

Finally, the reason map[1][1] doesn't work in the code above is that you read into the character array at map[0], then you attempt to output the string at map[1]. Change that to map[0] and you will get your string. Change it to map[0][0] and you will get the first character of map[0]. The two dimensional array syntax means that map[0][4] is the 5th character of the first string, and map[4][0] is the first character of the 5th string.

>>I know it involves nested for loops with increasing x and y values for a char[x][y] sort of set up, but I'm not sure how to get x and y there to point at proper points in the loaded file.

call me outdated and complex, but here's how they taught me back when i was in tenth grade. i know they lied to me about complexity, seing that nested for loops are n*n complexity ..here, tho' it wouldn't be that bad... it's just 10*10 complexity by my counts:)

Code:

---

...
fstream f("map/map01.txt", ios::in);//that's for opening the file
 for(int i=0; i<10;i++)
  for(int j=0;1<10;j++)
    f>>map[i][j];//and reading it into a "map", [10][10]array

---

...and then when you want to print it on screen you use the same kind of nested loops just that you have the "cout<<a[i][j]<<" "; the blank is optional, depending on your level of tidyness

----
sorry, it was ninth :D

Hm. Thought I tried doing that. Maybe I was opening it in binary mode or something. Which would explain a few things...

Granted, I'm not really sure this is the optimal method for using with a map engine anyway, but I guess I got a be stuck in my bonnet. Will try :P Thanks.

---edit---

Unfortunately, this did not work.
Fortunately, it was just because I forgot my fstream source wasn't anywhere NEAR where I had map00.txt. Hence, after I moved it around, all worked.

One thing I still don't get, though.

Code:

---

for(int i=0; i<10;i++)
  for(int j=0;1<10;j++)
    f>>map[i][j];//and reading it into a "map", [10][10]array

---

j is the y-axis in the 10x10 map array, isn't it? I thought it read files in from left to right. Wouldn'tthat require it to go top to bottom?

Or am I wrong about x/y correlation?

j is the x axis. If your file looks like this:

Code:

---

0123456789
abcdefghij
klmnopqrst
0123456789
abcdefghij
klmnopqrst
0123456789
abcdefghij
klmnopqrst
uvwxyzuvwx

---

Then map[0][0] will be '0' and map[0][1] will be '1' and map[0][9] will be '9' and map[1][0] will be 'a' and map[1][9] will be 'j' and map[9][9] will be 'x'.

Also, map[0] will be "0123456789" (with no terminating null character) and map[1] will be "abcdefghij" (again without a terminating null).