I have a barplot where the bars are located at the following x-coordinates:
1,2,3,4,5,6,7,8,9,10,12,14,16,18,20,22,24,26,28,30,35,40,45,50,55,60,70,80,90
As Adiel had mentioned, use:
set(gca,'Xtick', Vector);
You don't need xticklabel, unless you want ticks label texts that are different from the values at their positions.
xticklabel