# Topic string utility functions ### *group* Topic manipulation Topic string utility functions. ### Defines ### JSDRV_TOPIC_INIT Empty topic structure initializer. ### Functions ### void jsdrv_topic_clear(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic) Clear a topic structure instance to reset it to zero length. * **Parameters:** **topic** – **[inout]** The topic structure, which is modified in place. ### void jsdrv_topic_truncate(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic, uint8_t length) Truncate a topic structure to a specified length. If you store length before calling [jsdrv_topic_append()](#group__jsdrv__topic_1ga333bbb0247943f9c015a6675cd0c4337), you can use this function to revert the append. * **Parameters:** * **topic** – **[inout]** The topic structure, which is modified in place. * **length** – The desired length. ### void jsdrv_topic_append(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic, const char \*subtopic) Append a subtopic to a topic structure. This function intelligently adds the ‘/’ separator. If the topic does not already end with ‘/’, it will be inserted first. #### SEE ALSO [jsdrv_topic_remove](#group__jsdrv__topic_1gac2739877bfcc7fcea145a12cb6c1ed27) * **Parameters:** * **topic** – **[inout]** The topic structure, which is modified in place. * **subtopic** – The subtopic string to add. ### int32_t jsdrv_topic_remove(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic) Remove a subtopic from the end of a topic structure. This function intelligently removes the ‘/’ separator. If the topic already ends with ‘/’, then this it is ignored. This function then removes the “/subtopic”. The resulting topic does NOT end in ‘/’. #### SEE ALSO [jsdrv_topic_append](#group__jsdrv__topic_1ga333bbb0247943f9c015a6675cd0c4337) * **Parameters:** **topic** – **[inout]** The topic structure, which is modified in place. * **Returns:** The number of characters removed. ### void jsdrv_topic_set(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic, const char \*str) Set the topic to the provided value. This function will assert if no room remains. * **Parameters:** * **topic** – **[inout]** The topic structure, which is modified in place. * **str** – The desired topic value. ### void jsdrv_topic_suffix_add(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic, char ch) Adds a suffix character to the topic. This function will assert if no room remains. * **Parameters:** * **topic** – **[inout]** The topic structure, which is modified in place. * **ch** – The special character to append. ### char jsdrv_topic_suffix_remove(struct [jsdrv_topic_s](#_CPPv413jsdrv_topic_s) \*topic) Remove the suffix character from a topic. * **Parameters:** **topic** – **[inout]** The topic structure, which is modified in place. * **Returns:** ch The suffix character removed or 0 if no character was removed. ### struct jsdrv_topic_s *#include * The topic structure. ### Public Members ### char topic[JSDRV_TOPIC_LENGTH_MAX] The topic string. ### uint8_t length The length in bytes ignoring the null terminator.