Version of pgmio.c that works with dynamic arrays from arralloc.c

pgmio2.c

/* Revised to be readable code and behave as a normal person would expect
 * when working with dynamic arrays from arralloc.c
 * s1563256, 10.11.2015
 */

/*
 * This file contains C routines for the MPI Casestudy.
 *
 *  To access these routines, add the following to your program:
 *
 *    #include "pgmio2.h"
 *
 *  Note: you MUST link with the maths library -lm to access fabs etc.
 */


#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "pgmio2.h"
#define MAXLINE 128

/*
 *  Routine to get the size of a PGM data file
 *
 *  Note that this assumes a single line comment and no other white space.
 */

void pgmsize(char *filename, int *width, int *height) { 
    
    FILE *fp;
    char dummy[MAXLINE];
    int n = MAXLINE;

    if (NULL == (fp = fopen(filename,"r"))) {
        fprintf(stderr, "pgmsize: cannot open <%s>\n", filename);
        exit(-1);
    }

    // Ignore the first two lines
    fgets(dummy, n, fp);
    fgets(dummy, n, fp);

    // Read dimensions
    fscanf(fp,"%d %d", width, height);

    fclose(fp);
}


// Reads .pgm to a 2D floating point array. 
// E.g. to float** arr = arralloc(sizeof(float), 2, height, width)
// The array must be dynamically allocated (use pointers for indexing).
// Note that this assumes a single line comment and no other white space.

void pgmread(char *filename, float **data, int width, int height) { 

    FILE *fp;
    int width_read, height_read;
    int i, j;
    char dummy[MAXLINE];
    
    if (NULL == (fp = fopen(filename,"r"))) {
        fprintf(stderr, "pgmread: cannot open <%s>\n", filename);
        exit(-1);
    }

    // Ignore first two lines
    fgets(dummy, MAXLINE, fp);
    fgets(dummy, MAXLINE, fp);

    // Read dimensions
    fscanf(fp,"%d %d",&width_read, &height_read);

    // If dimensions not as expected, exit
    if ( width != width_read || height != height_read) {
        fprintf(stderr,
        "pgmread: size mismatch, (width,ny) = (%d,%d) expected (%d,%d)\n",
        width_read, height_read, width, height);
        exit(-1);
    }

    // Read max value and ignore
    fscanf(fp,"%d",&i);

    // Read pixel values into array
    for (i = 0; i < height; i++)
        for (j=0; j < width; j++)
            fscanf(fp,"%f", &data[i][j]);

    fclose(fp);
}

// Writes .pgm from a 2D floating point array. 
// E.g. from float** arr = arralloc(sizeof(float), 2, height, width)
// The array must be dynamically allocated (use pointers for indexing).

void pgmwrite(char *filename, float **data, int width, int height) {
    
    FILE *fp;
    int i, j, grey;
    float xmin, xmax;
    float maxval = 255.0;

    if (NULL == (fp = fopen(filename,"w"))) {
        fprintf(stderr, "pgmwrite: cannot create <%s>\n", filename);
        exit(-1);
    }

    printf("Writing %d x %d picture into file: %s\n", width, height, filename);

    // Find the max and min absolute values of the array
    find_extrema(data, width, height, &xmin, &xmax);

    fprintf(fp, "P2\n");
    fprintf(fp, "# Written by pgmio::pgmwrite\n");
    fprintf(fp, "%d %d\n", width, height);
    fprintf(fp, "%d\n", (int) maxval);

    for (i = 0; i < height; i++) {
        for (j = 0; j < width; j++) {

            grey = maxval * ((fabs(data[i][j])-xmin)/(xmax-xmin))+0.5;
            fprintf(fp, "%3d ", grey);
    
            // Ensure line length < 70. 16 * 4 characters= 64. %3d prints padded to 3 chars.
            if ( (i * width + j) % 16 == 0)
                fprintf(fp, "\n");
        }
    }
    fclose(fp);
}

// Helper functions. Find min and max in 2D array.
void find_extrema(float **data, int width, int height, float *min, float *max) {

    float xmin = fabs(data[0][0]);
    float xmax = fabs(data[0][0]);

    for (int i=0; i<height; i++) {
        for (int j=0; j<width; j++) {
            if (fabs(data[i][j]) < xmin)
                xmin = fabs(data[i][j]);
            if (fabs(data[i][j]) > xmax)
                xmax = fabs(data[i][j]);
        }
    }

    if (xmin == xmax)
        xmin = xmax-1.0;

    *min = xmin;
    *max = xmax;
}

pgmio2.h

void pgmsize (char *filename, int *nx, int *ny);
void pgmread (char *filename, float **vx, int nx, int ny);
void pgmwrite(char *filename, float **vx, int nx, int ny);
void find_extrema(float **, int, int, float*, float*);