View source for Code:number-pairs-to-array-file.c

The main use-case of this code, is to take certain SQL results and convert them to array files that can be used in the [[Code:isochromic.c|image generator]].

Example of how this was used: The results of a query in [[Code:food1.sql]] were used to generate [[:File:yields.data-float64-895x1]] which was used in generating [[:File:food-crop-production1.png]].

==Code==
<syntaxhighlight lang="c">
// takes pairs of numbers from stdin
// reads them as "index" and "value"
// puts them into an array
// saves the array to an output file
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <ctype.h>

#define MAXSIZE 1048576
int size=0;
char *name="out";
double default_value=NAN;
double a[MAXSIZE];

int main(int argc, char **argv) {
 if (argc >= 2) { char *p=argv[1]; while (*p && (*p=='-'||*p=='_'||isalnum(*p))) p++; if (!*p) name = argv[1]; }
 if (argc >= 3) default_value = atof(argv[2]);
 for (int i=0; i<MAXSIZE; i++) a[i] = default_value;
 while (1) {
  double index, value;
  if (scanf("%lf %lf", &index, &value) != 2) break;
  int i = index;
  if (i < 0)        { printf("Index can't be negative\n"); continue; }
  if (i >= MAXSIZE) { printf("Index too big, can't add it\n"); continue; }
  if (i >= size) size = i+1;
  a[i] = value;
 }
 char filename[256];
 sprintf(filename, "data/%s.data-float64-%dx1", name, size);
 FILE *f = fopen(filename, "w");
 if (!f) { perror(filename); return 1; }
 printf("Writing file: %s\n", filename);
 fwrite(a, sizeof(double), size, f);
 fclose(f);
 return 0;
}
</syntaxhighlight>