The sub-pattern cN (N is greater than 0, like 'c27') is used to indicate a fixed-length field of 'N' bytes. A pointer to the first byte in the field will be put into the current field of the cmd struct, and the offset will be advanced by 'N' bytes. The 'c' token consumes one field in the cmd struct.
The assumption is that the programmer knows that this unsigned char * field points to a char buffer of 'N' bytes. No "l_" value is expected in the cmd struct, no preceding length byte or bytes is expected in the p_cmd data, and no l_ value is supplied to assist the programmer. If 'l_' type information is expected or required, use a 'v' token instead.