what str2num will perform?

fid = fopen(txtfile,'r'); 
tline = fgetl(fid); 
index = findstr(tline,'.'); 
    i = i+1;
    filenames(i) = str2num(tline(1:index-1))+1;    

what is the function of str2num here? I am not getting clear with the mathwork help. Can anyone explain in brief?

[Adam]

It converts a string to a number, if such a conversion makes sense.

You can just try it on your command line, e.g.

str2num( '17' )

Surely

doc str2num

is fairly clear though?! It gives clear examples.

[Rik]

As the documentation mentions, str2num uses eval and might thus have unintended side effects, which you can avoid by using str2double. In most cases these two functions should be equivalent.