Libmosquitto missing mosquitto_int_option()

I need to explicitly set outgoing in-flight messages to be 1 so that there would be only last message duplicates at QoS=1. But libmosquitto (mosquitto.h) version 1.5.0 I use is missing mosquitto_int_option() call. Any other way to achieve the setting of ‘MOSQ_OPT_SEND_MAXIMUM’ to 1?

I’m afraid that mosquitto_int_option() was introduced in version 1.6, and so was MOSQ_OPT_SEND_MAXIMUM. I’d strongly suggest that you upgrade to something more recent if you need this feature.