This code creates a label that is line-wrapped and left-aligned:

char *long_string = "...";
GtkWidget *label = gtk_label_new (long_string);
gtk_misc_set_alignment (GTK_MISC (label), 0, 0.5);
gtk_label_set_line_wrap (GTK_LABEL (label), TRUE);
gtk_label_set_max_width_chars (GTK_LABEL (label), 40);
gtk_widget_show (label);

This works fine, but GtkMisc is deprecated, so I want to replace the call to gtk_misc_set_alignment with gtk_widget_set_halign, the documented replacement:

gtk_widget_set_halign (label, GTK_ALIGN_START);

But this doesn't work. The label widget's allocation is left-aligned, but the text inside the label is shifted towards the center.