Read array of a file diagonally

Question

Hello!

I have a fixed-size file that has a random character array. However I’m having trouble using fseek and fread to read the file diagonally.

To explain the problem, I need to do a kind of word search that searches the words horizontally, vertically and diagonally.

super reduced matrix example:

nwlrbbmqbh
cdarzowkky
hiddqscdxr
jmowfrxsjy
bldbefsarc
bynecdyggx
xpklorelln
mpapqfwkho
pkmcoqhnwn
kuewhsqmgb

NOTE: I can’t throw it in memory.

Answer 1

Follows a program capable of reading words arranged horizontally, vertically and diagonally in a word search contained in a text file.

Words can be accessed through their coordinates:

#include <string.h>
#include <stdlib.h>
#include <stdio.h>


typedef enum {
    eHorizontal,
    eVertical,
    eDiagonal
} orientacao_t;


char obter_letra( int col, int linha, FILE * pf )
{
    char buf[1024] = {0};

    rewind(pf);

    while( 0 <= linha-- )
        fgets( buf, sizeof(buf), pf );

    return buf[ col ];
}


char * obter_palavra( char * p, int col, int linha, int tam, orientacao_t or, FILE * pf )
{
    int i = 0;

    for( i = 0; i < tam; i++ )
    {
        switch( or )
        {
            case eHorizontal :
                p[i] = obter_letra( col + i, linha, pf );
                break;

            case eVertical:
                p[i] = obter_letra( col, linha + i, pf );
                break;

            case eDiagonal:
                p[i] = obter_letra( col + i, linha + i, pf );
                break;

            default:
                break;
        }
    }

    p[tam] = '\0';

    return p;
}


int main( int argc, char * argv[] )
{
    char palavra[50] = {0};
    FILE * pf = NULL;

    pf = fopen( argv[1], "r" );

    printf( "Palavra 1: %s\n", obter_palavra( palavra,  11,  2,  8, eDiagonal,   pf ) );
    printf( "Palavra 2: %s\n", obter_palavra( palavra,   7, 18, 10, eHorizontal, pf ) );
    printf( "Palavra 3: %s\n", obter_palavra( palavra,   5,  8,  8, eVertical,   pf ) );
    printf( "Palavra 4: %s\n", obter_palavra( palavra,   10, 6, 8,  eDiagonal, pf ) );
    printf( "Palavra 5: %s\n", obter_palavra( palavra,   9, 16,  4, eHorizontal, pf ) );
    printf( "Palavra 6: %s\n", obter_palavra( palavra,   18,  16,  4, eVertical,   pf ) );

    fclose(pf);

    return 0;
}

Test file containing the words VERTICAL, HORIZONTAL, DIAGONAL, GATO, CACHORRO and RATO:

CAQIXCBXXJMDVRANWPMT
YGOQZMQWVKMMJMSIAQDI
XFXOBRWILQJDJYORKGWC
UARIHCBJSDTLIEBSETOH
QSLOCAWZFUYXBASBJTCC
NLJDHZMWYMLVPVGWPNAZ
BBTOCWHEYVCDNGPOLHXO
SDICESRPTQPARRLNNSHZ
XMSKYVIGVDZLCEBBIAOW
UTZABEBHKJNTEHFNPILH
GINPIRMZTJJVLIOZHRRE
NJFRQTLRHBQOSNQRIWOX
CBJTPIEDNWBJKGDJRTIC
SRTWSCSPWFHEMKYGYOXU
OYSCYAPEDMABBFJBZSZN
RQVSILWPWOGNREWNKHHE
JBXFOFFYGGATOJLUMORV
FNVLDATMISHLTVIZEDAL
DZADHEZHORIZONTALXTC
MXOPRHRNNNBXMZNHUOOG

Exit:

Palavra 1: DIAGONAL
Palavra 2: HORIZONTAL
Palavra 3: VERTICAL
Palavra 4: CACHORRO
Palavra 5: GATO
Palavra 6: RATO