I have a porblem with reading a raspberry pi file in a fuction. I get the Erro: Call to MATLAB function aborted: Invalid file identifier. Use fopen to generate a valid file identifier.

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persistent sensorPath;
if isempty(sensorPath)
path = '/sys/bus/w1/devices/10-0008032a1531';
fileSeperator = '/';
sensorPath = [path,fileSeperator,'w1_slave'];
end
% Open file, read, and close it
fid = fopen(sensorPath);
w1_slave = fread(fid,1024);
fclose(fid);

Answers (2)

Ankitha Kollegal Arjun
Ankitha Kollegal Arjun on 18 Apr 2017
Check the value of 'fid' obtained. You can add the following lines to your code:
if fid == -1
error('File not found')
end
If the value of fid is -1, then it is likely that the file is not located in the supplied path.
Also, check if the unique sensor ID supplied in the path (10-0008032a1531) is the right one.

Stephen23
Stephen23 on 18 Apr 2017
Edited: Stephen23 on 18 Apr 2017
The best solution is to always return fopen's second output message, and use it to display exactly what occurred when fopen tried to open the file:
[fid,msg] = fopen(...)
assert(fid>=3,msg)
Anyone who tells you to check the value of fid but does not tell you to get the second output is only telling you half of the answer!

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