This avoids the following false positive from gcc:
config.c:352:28: error: 'df' may be used uninitialized [-Werror=maybe-uninitialized]
352 | dst->val.d = df;
| ^
config.c: In function 'config_read':
config.c:286:16: note: 'df' was declared here
286 | double df;
| ^
This avoids the following false positive from gcc: