QPushButton *left = new QPushButton("killin' kind");
QPushButton *right = new QPushButton("Emma");

QHBoxLayout *layout = new QHBoxLayout(this);

layout->addWidget(left);
layout->addStretch();
layout->addWidget(right);

QSizePolicy policy = left->sizePolicy();
policy.setHorizontalStretch(1);
policy.setVerticalStretch(1);
policy.setHorizontalPolicy(QSizePolicy::Minimum);
left->setSizePolicy(policy);

policy = right->sizePolicy();
policy.setVerticalStretch(1);
policy.setHorizontalStretch(3);
policy.setHorizontalPolicy(QSizePolicy::Minimum);
right->setSizePolicy(policy);