Thread: Segfault in reading file stream

For a C++ project, we need to fill in code to play Sudoku. File handling and command input are already in, but we need to write initialization, configuration, output, and adding/erasing values from the board.

To configure the board, we need to read from an input file that has a structure of:

Code:

###\n
###\n
###\n        etc.

where the three #s are integers representing row, column, and value at that point.

I am trying to use fscanf to fill in the Sudoku grid, yet am running into segmentation faults. I have looked at various resources available to me, including similar topics on this forum, and have yet to work out a solution.

My code (currently) looks like:

Code:

void configure(FILE *puzzle_file) {

        int row ;
        int col ;
        int dig ;

        while( !feof(puzzle_file) ) {
                fscanf(puzzle_file, "%d%d%d", &row, &col, &dig) ;
                puzzle[row][col] = dig ;
                fixed[row][col] = TRUE ;
        }

}

Opening the file and the error checking that comes with it is already handled in the code given to me. This is the only method that actually reads the file.

Any stdio function that reads from the file causes a segfault. I have absolutely no idea what the problem could be, so I need your assistance to identify it.

Yeah I actually got that and fixed it with:

Code:

fscanf(puzzle_file, "%1d%1d%1hd", &row, &col, &val)

Regardless, I now had to check for errors in the input file and read in each field as a string anyway. Lines can have more than 3 characters in them, and I'm supposed to just ignore everything past those first ones.

Code:

void configure(FILE *puzzle_file) {

        int row = 0 ;
        int col = 0 ;
        short val = 0 ;

        char linestr[100] ;

        int fline = 1 ;

        while( fscanf(puzzle_file, "%s\n", linestr) != EOF ) {
                row = linestr[0]-48 ; col = linestr[1]-48 ; val = linestr[2]-48 ;
                if( !in_range(row) || !in_range(col) || !in_range(val) ) {
                        printf("Illegal format in configuration file at line %d\n", fline) ;
                        exit(1) ;
                }
                if( puzzle[row][col] != 0 ) {
                        printf("Illegal placement in configuration file at line %d\n", fline) ;
                        exit(1) ;
                }
                puzzle[row][col] = val ;
                fixed[row][col] = TRUE ;
                fline++ ;
        }

        return ;

}

This works perfectly well. Everything compiles and runs smoothly. Thing is, does checking against EOF work the same as using feof? I assume no, but I can't be sure.