what is the error 'Error using fscanf Invalid file identifier. Use fopen to generate a valid file identifier.'

after coding this

clear

clc

k=1:25:601;

for i=1:numel(k)

basefilename=sprintf('porosity_k%d',k(i));

fullfilename=fullfile(basefilename);

fileid= fopen(fullfilename,'r+')

A(:,i)=fscanf(fileid,'%f')

fclose(fileid)

end

B=cat(1,A(:,1),A(:,2),A(:,3),A(:,4),A(:,5),A(:,6),A(:,7),A(:,8),A(:,9),A(:,10),...

A(:,11),A(:,12),A(:,13),A(:,14),A(:,15),A(:,16),A(:,17),A(:,18),A(:,19),A(:,20),...

A(:,21),A(:,22),A(:,23),A(:,24),A(:,25));

i get this error

Error using fscanf Invalid file identifier. Use fopen to generate a valid file identifier

please help me why i get this error