Read & parse voltage & current data

diff --git a/batteryviewer.c b/batteryviewer.c
index 65d70091b118606d32376ebd92c7472b698dcbe6..1c38b3cca8527a36052023be1d85a54c5863c453 100644 (file)
--- a/batteryviewer.c
+++ b/batteryviewer.c
@@ -1,12 +1,50 @@
 #include "chart.h"
+#include <ctype.h>
+#include <errno.h>
 #include <gtk/gtk.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+const char voltage_filename[] = "/sys/class/power_supply/BAT0/voltage_now";
+const char current_filename[] = "/sys/class/power_supply/BAT0/current_now";
 
 struct State {
   BVChart *voltage;
   BVChart *current;
 };
 
+static float fatof(const char *filename) {
+  FILE *f = fopen(filename, "r");
+  if (f == NULL) {
+    return NAN;
+  }
+
+  const int bufsize = 1024;
+  char buf[bufsize];
+  const int read = fread(buf, sizeof(char), bufsize, f);
+  if (read == 0 || read == bufsize || ferror(f)) {
+    fclose(f);
+    return NAN;
+  }
+  fclose(f);
+
+  char *end;
+  errno = 0;
+  float val = strtof(buf, &end);
+  int parsed = end - buf;
+  gboolean parsed_all = parsed == read;
+  gboolean parsed_all_but_space = parsed == read - 1 && isspace(*end);
+  gboolean parse_ok = parsed_all || parsed_all_but_space;
+  if (errno != 0 || parsed == 0 || !parse_ok) {
+    return NAN;
+  }
+  return val;
+}
+
 static gboolean collect_data(struct State *state __attribute__((unused))) {
+  fprintf(stderr, "Voltage: %f, current: %f\n", fatof(voltage_filename),
+          fatof(current_filename));
   return TRUE;
 }