Pebble strtol test #1. This shows strtol returning 0 when compiled with SDK 1.12. When numstr is set to "-37" it causes a runtime crash.

strtol-test1.c

#include "pebble_os.h"
#include "pebble_app.h"
#include "pebble_fonts.h"

#define MY_UUID { 0x92, 0x40, 0x44, 0xC0, 0xCA, 0x8A, 0x43, 0x64, 0x9D, 0xDE, 0x11, 0x33, 0x6F, 0x04, 0xA9, 0x3F }
PBL_APP_INFO(MY_UUID,
             "strtol test", "Your Company",
             1, 0, /* App version */
             DEFAULT_MENU_ICON,
             APP_INFO_STANDARD_APP);

Window window;
TextLayer textlayer;

char outstr[20];

void handle_init(AppContextRef ctx) {

  window_init(&window, "Window Name");
  window_stack_push(&window, true /* Animated */);

  text_layer_init(&textlayer, GRect(10, 10, 100, 100));
  layer_add_child(&window.layer, &textlayer.layer);

  text_layer_set_text(&textlayer, "calling strtol");
  char numstr[] = "37";
  long mynum = strtol(numstr, NULL, 10);
  snprintf(outstr, 19, "strtol returned: %ld", mynum);
  text_layer_set_text(&textlayer, outstr);
}


void pbl_main(void *params) {
  PebbleAppHandlers handlers = {
    .init_handler = &handle_init
  };
  app_event_loop(params, &handlers);
}