Help with virtual chessboard file input/output | Together C & C++ | Page 1

still bobcat May 15, 2025, 11:28 AM

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seeking help with accurate file/input output for a .txt file representation of a chess game

glacial spruceBOT May 15, 2025, 11:28 AM

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still bobcat May 15, 2025, 11:29 AM

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8       bR  bN  bB  bQ  bK  bB  bN  bR       8
7       bp  bp  bp  bp  bp  bp  bp  bp       7
6       .   .   .   .   .   .   .   .        6
5       .   .   .   .   .   .   .   .        5
4       .   .   .   .   .   .   .   .        4
3       .   .   .   .   .   .   .   .        3
2       wp  wp  wp  wp  wp  wp  wp  wp       2
1       wR  wN  wB  wQ  wK  wB  wN  wR       1

        a   b   c   d   e   f   g   h```

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if(set[i]->getName() == "Pawn" || set[i]->getName() == "King" || set[i]->getName() == "Knight") {
                        cout << "Where would you like to move the " << set[i]->getName() << " at " << userInput << "?" << endl;
                    }
                    pos = evaluateMoves(set[i], board, set, turn);


                    for(int j = 0; j < ((8 - V_input) + 3); j++) { // skips rows to row position
                        getline(file,line);
                    }
                    string letter;
                    int intPutH = (H_input - 96);
                    file >> letter;
                    for(int j = 0; j < (intPutH - 2); j++) {
                        file >> letter;
                    }
                    file << "  .  ";
                    file.seekg(0);          ```

analog umbra May 15, 2025, 11:30 AM

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Alright if you can tell me when something goes wrong vs how it's supposed to look

still bobcat May 15, 2025, 11:30 AM

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unfortunately this project is due in 3.5 hours, so i don't think i'll get it done in time

analog umbra May 15, 2025, 11:30 AM

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It'll be a big help

still bobcat May 15, 2025, 11:30 AM

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yeah for sure

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so the rows are working fine

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but the columns aren't

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8       bR  bN  bB  bQ  bK  bB  bN  bR       8
7       bp  bp  bp  bp  bp  bp  bp  bp       7
6       .   .   .   .   .   .   .   .        6
5       .   .   .   .   .   .   .   .        5
4       .   .   .   .   .   .   .   .        4
3       .   .   .   .   .   .   .   .        3
2      .    wp  wp  wp  wp  wp  wp  wp       2
1       wR  wN  wB  wQ  wK  wB  wN  wR       1

        a   b   c   d   e   f   g   h```

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this is the result after a move from b2.

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it's not in the right spot, and it's not even accurate in the place it's set (a2)

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8       bR  bN  bB  bQ  bK  bB  bN  bR       8
7       bp  bp  bp  bp   .  bp  bp  bp       7
6       .   .   .   .   .   .   .   .        6
5       .   .   .   .   .   .   .   .        5
4       .   .   .   .   .   .   .   .        4
3       .   .   .   .   .   .   .   .        3
2      .    wp  wp  wp  wp  wp  wp  wp       2
1       wR  wN  wB  wQ  wK  wB  wN  wR       1

        a   b   c   d   e   f   g   h```

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calling a move for d7 from black results in another close yet inaccurate replacement

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e2, however, works fine

analog umbra May 15, 2025, 11:35 AM

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So your columns are shifting but somehow e2 works blink1

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Is e column the only one that works?

still bobcat May 15, 2025, 11:35 AM

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i think so

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nope, d2 works too

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only for white though

analog umbra May 15, 2025, 11:38 AM

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Just a thought

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Is H_input a string or char?

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As in the type

still bobcat May 15, 2025, 11:38 AM

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char

analog umbra May 15, 2025, 11:39 AM

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Try changing letter to char

still bobcat May 15, 2025, 11:42 AM

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aw man i really thought i had it for a sec

analog umbra May 15, 2025, 11:42 AM

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I think your main issue is that your board representation is super funky

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Making you do some weird ways to manipulate it

still bobcat May 15, 2025, 11:42 AM

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yeah haha that's fair

analog umbra May 15, 2025, 11:44 AM

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I'd suggest another way but you're time bound

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So we'll have to work with it

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What's with the -2 and +3 when you're looping?

still bobcat May 15, 2025, 11:46 AM

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the 8 - V_input + 2 (fixed that earlier) is to reverse the orientation of the position

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lemme word that better

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it makes it so that the vertical values line up with the values of the board, since they're sort of inverse of each other

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so a V_input of 7 corresponds to line 4 (since getline ignores the blank 2 line)

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and V_input 3 would correspond to line 8

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as for the -2, that's just me trying to figure the rows out

analog umbra May 15, 2025, 11:51 AM

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Okay I think I can't really help anymore

still bobcat May 15, 2025, 11:51 AM

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yeah you know that's really fair

analog umbra May 15, 2025, 11:51 AM

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Try compiling your code with -Wall -Wextra

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And use a debugger

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Vscode should be able to interface with it

analog umbra May 15, 2025, 11:52 AM

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analog umbra Okay I think I can't really help anymore

Maybe I could've if I had my computer and was able to run the code locally but I'm in school rn

still bobcat May 15, 2025, 11:52 AM

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that's fair

analog umbra May 15, 2025, 11:52 AM

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Well good luck

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Hope yoy get your assignment in on time

still bobcat May 15, 2025, 11:53 AM

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i appreciate you spending the time trying to help me

mighty bolt May 15, 2025, 12:20 PM

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file >> letter is reading tokens seperated by whitespace instead of chars

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and your squares use fixed-spacing not whitespaced seperated tokens

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but >> skips whitespace so it wont go through the columns properly

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why dont u just read the entire line as a string and then change ur column logic based on a fixed-width format like each square = 4 characters

still bobcat May 15, 2025, 12:24 PM

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that's what i've been trying to do but it never seems consistent

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i'm trying to use file.ignore(4) to iterate forward

mighty bolt May 15, 2025, 12:25 PM

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that skips 4 bytes iirc

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not 4 characters

still bobcat May 15, 2025, 12:25 PM

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oh?

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how would i move forward on a fixed scale?

mighty bolt May 15, 2025, 12:26 PM

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treat each row as a fixed-width string and move forward in blocks of chars

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so like

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lets say:

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int baseOffset = 8;

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int squareWidth = 4;

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file.seekg(lineStart + fromColOffset);```

glacial spruceBOT May 15, 2025, 12:29 PM

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@mighty bolt

It looks like you may have code formatting errors in your message

Note: Make sure to use back-ticks (`) and not quotes (')
Note: Make sure to specify a highlighting language, e.g. `cpp`, after the back-ticks

Markup

```cpp
int main() {}
```

Result

int main() {}

mighty bolt May 15, 2025, 12:32 PM

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int baseOffset = 8;                
int squareWidth = 4;              

int rowOffset = (8 - V_input);    

for(int j = 0; j < rowOffset + 1; j++) {
    getline(file, line);         
}

std::streampos lineStart = file.tellg(); 
int fromColOffset = baseOffset + (H_input - 'a') * squareWidth; // 
file.seekg(lineStart + fromColOffset); 

file << " .  ";  

file.seekg(0);

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make sure you use fstream when you open the file btw cause you can't seekg and << with ifstream

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does that make sense?

still bobcat May 15, 2025, 12:35 PM

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tbh not really

mighty bolt May 15, 2025, 12:36 PM

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okay so

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we have a fixed-width chessboard

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each square is exactly 4 characters wide

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we want to seek the exact char position in the file that maches a square, like b2

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if we want to move a piece from b2, chess row 2 -> index = 8 - 2 = 6 starting from top as 8

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in this case we want the 7th line (arrays start from 0)

still bobcat May 15, 2025, 12:37 PM

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char letter;
                        file.seekg (8, std::ios::cur);      
                    for(char j = 'a'; j != H_input; j++) {
                        file.seekg (4, std::ios::cur);      
                    }
                    file << ".   ";
                    file.seekg(0);     ```

mighty bolt May 15, 2025, 12:38 PM

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i see somebody typing whos been going on about a chess engine for a while

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he may be able to explain / add onto what i've said better than myself

still bobcat May 15, 2025, 12:38 PM

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this is what i was trying but this still gives me irregular results

mighty bolt May 15, 2025, 12:39 PM

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yeah so the layout of the file and position math won't be matching up

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if its irregular

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i'll wait to see what this guy says

last geyser May 15, 2025, 12:39 PM

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@still bobcat Another option, if you're interested, is using the backend of say my Chess Engine. If you want, I can get on call with you and help you quickly set this up.

That way, you can just handle the display of the board (which is as simple as reading from an array and printing stuff) and all the moving piece logic will be handled by the chess engine's backend (which is super fast if you care about that, but more importantly, battle-tested and correct).

mighty bolt May 15, 2025, 12:40 PM

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atlas this is part of a school project right

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do they specify if you're allowed to use other projects

still bobcat May 15, 2025, 12:40 PM

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yeah, i can't do that

mighty bolt May 15, 2025, 12:40 PM

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dang

last geyser May 15, 2025, 12:40 PM

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Ah. I see. Are you sure your piece movement logic is correct? @still bobcat

still bobcat May 15, 2025, 12:41 PM

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yeah, i'm pretty sure, but the visuals aren't solidly connected to the movement logic

mighty bolt May 15, 2025, 12:41 PM

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a b c d e f g h ← line 0
8 bR bN bB bQ bK bB bN bR 8 ← line 1 (rank 8)
7 bp bp bp bp bp bp bp bp 7 ← line 2 (rank 7)
...
1 wR wN wB wQ wK wB wN wR 1 ← line 8 (rank 1)
a b c d e f g h ← line 9

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if we want to modify rank 2 in this case, you should skip 1 (header) and + 6 (ranks 8 to 3)

still bobcat May 15, 2025, 12:41 PM

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it's a little odd and janky but it's what i have for having worked on this for the past 15 hours straight

mighty bolt May 15, 2025, 12:41 PM

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so its 6 lines to get to rank 2

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7 sorry

last geyser May 15, 2025, 12:42 PM

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still bobcat yeah, i'm pretty sure, but the visuals aren't solidly connected to the movement ...

I ask because it's one of the hardest thing to get right in chess.

still bobcat May 15, 2025, 12:42 PM

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i can send what i've got

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i haven't worked in check or mate or any of that but i don't have time for that

last geyser May 15, 2025, 12:42 PM

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Also, your row and column is +1 at least, maybe even +2 because you have an extra label row/column

mighty bolt May 15, 2025, 12:43 PM

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int rowInFile = 1 + (8 - V_input);  // 1 = skip header row
for (int j = 0; j < rowInFile; j++) {
    getline(file, line);
}

still bobcat May 15, 2025, 12:43 PM

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📎 message.txt

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sorry for the .txt file

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i'm not a professional, evidently

last geyser May 15, 2025, 12:44 PM

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i mean, i can't really validate that for correction..

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Typically, you'd perform this test https://www.chessprogramming.org/Perft_Results

Perft Results

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If you can match depth 6-7 results for most positions, your move-generation is correct.

mighty bolt May 15, 2025, 12:45 PM

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oh dude

still bobcat May 15, 2025, 12:45 PM

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imma be honest, i got no clue what any of that is

mighty bolt May 15, 2025, 12:45 PM

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(positionH - 95)

still bobcat May 15, 2025, 12:45 PM

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this is just a pass-and-play chess game

mighty bolt May 15, 2025, 12:45 PM

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sort that

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int colIndex = positionH - 'a' + 1;

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that maps 'a'..'h' and 1..8 cleanly which would affect board.getOccupied() and board.flipOccupied()

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@still bobcat do you get why -95 is an issue

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board.getOccupied(positionV, positionH - 95);
with 'b' - 95 = 3 you check column 3 but b is column 2

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you're shifting everything 1 column to the right

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every call thats (positionH - 95) should be:
(positionH - 'a' + 1)

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give that a go

still bobcat May 15, 2025, 12:59 PM

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okay i will

mighty bolt May 15, 2025, 1:01 PM

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board.flipOccupied(piece->getPositionV(), (piece->getPositionH() - 96), true);

should be:

if(board.getOccupied(positionV + i, col))
board.flipOccupied(piece->getPositionV(), piece->getPositionH() - 'a' + 1, true);

glacial spruceBOT May 15, 2025, 1:01 PM

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@mighty bolt

It looks like you may have code formatting errors in your message

Note: Make sure to use back-ticks (`) and not quotes (')
Note: Make sure to specify a highlighting language, e.g. `cpp`, after the back-ticks

Markup

```cpp
int main() {}
```

Result

int main() {}

mighty bolt May 15, 2025, 1:03 PM

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so:

positionH - 95 should be position H - 'a' + 1

positionH - 96 should be positionH - 'a' + 1

piece->getPositionH() - 95 should be piece->getPositionH() - 'a' + 1
piece->getPositionH() - 96 should be piece->getPositionH() - 'a' + 1

still bobcat May 15, 2025, 1:04 PM

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warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: 421 | file.seekg(lineStart + fromColOffset);

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note: candidate 2: 'operator+(std::streamoff {aka long long int}, int)' (built-in) 421 | file.seekg(lineStart + fromColOffset);

mighty bolt May 15, 2025, 1:05 PM

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ah sorry

still bobcat May 15, 2025, 1:05 PM

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all good, i just don't know what it means

mighty bolt May 15, 2025, 1:05 PM

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linestart is a std::streampos and fromColOffSet is an int so theres two candidates for + and it doesnt know what to use

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change file.seekg(lineStart + fromColOffset);

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to: file.seekg(lineStart + static_cast<std::streamoff>(fromColOffset));

still bobcat May 15, 2025, 1:07 PM

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ah, now it's worse

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it's not in the right row anymore either now

mighty bolt May 15, 2025, 1:08 PM

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wat

still bobcat May 15, 2025, 1:08 PM

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idk but i do have to go and i'm so sorry and so thankful for your guys' help

mighty bolt May 15, 2025, 1:08 PM

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alright man well atleast you have something to hand in

#Help with virtual chessboard file input/output