转自：http://wzw19191.blog.163.com/blog/static/13113547020103218265162/
/* property_get: returns the length of the value which will never be
** greater than PROPERTY_VALUE_MAX - 1 and will always be zero terminated.
** (the length does not include the terminating zero).
**
** If the property read fails or returns an empty value, the default
** value is used (if nonnull).
*/
int property_get(const char *key, char *value, const char *default_value);
/* property_set: returns 0 on success, < 0 on failure
*/
int property_set(const char *key, const char *value);