You're reading the documentation for an older, but still supported version (1.33.4).
For information on the latest version, please have a look at 1.33.5.

addto

This function takes a source joint position (fSourcePos) and an offset vector (fOffset), and returns NULL. To add a joint offset, add fOffset to fSourcePos in your own code, as in the example below.

Definition
DRFLEx.h within class CDRFLEx, public section

LPROBOT_POSE addto(
    float fSourcePos[NUM_JOINT],
    float fOffset[NUM_JOINT]
) {
    return _addto(_rbtCtrl, fSourcePos, fOffset);
};

Parameter

Parameter Name	Data Type	Default Value	Description
fSourcePos	float[6]		Base joint position of the robot (J1–J6).
fOffset	float[6]		Offset values (ΔJ1–ΔJ6) to be added to the source position. Units are [deg].

Return

Value	Description
LPROBOT_POSE	NULL. See the Caution below.

Caution

The returned pointer is NULL; do not use it. Add fOffset to fSourcePos in your own code, as in the example below.

Example

float q_base[6] = { 0.f, 90.f, 0.f, 90.f, 0.f, 0.f };
float dq[6]     = { 5.f, -5.f, 0.f, 0.f, 0.f, 0.f };

float q_target[6];
for (int i = 0; i < 6; ++i)
    q_target[i] = q_base[i] + dq[i];

drfl.movej(q_target, 50, 20);

This example adds a small offset dq to the base joint position q_base in the application, which gives the summed joint pose (source + offset). The robot then moves to the updated joint configuration using movej().