Strange case of Code analyzer and if-else block

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AlireaA Mirrabie
AlireaA Mirrabie 2024-9-20
评论： AlireaA Mirrabie 2024-9-21
While running a simple if-else statement, I encountered a rather strange situation. In one part of my code, I have a section that generates a signal based on user choice via a dropdown menu. The code is referenced from the @CES_matlabinthemiddleeast YouTube channel, but I have made some changes. Here’s the relevant part of the code:
Fs = 1000; % Sampling rate
T = 1/Fs; % Sampling time
t = 0:T:1-T; % Time vector
mySig = zeros(1, length(t)); % Preallocation for generated signal
frq = [20, 40, 80, 160]; % Frequency vector
lenFrq = numel(frq); % Length of frequency vector
sigType = 'stationary';
% sigType = 'non-stationary'; % just imagin it's a drop down menu.
if strcmp(sigType, 'stationary')
mySig = 0.25 * sum(cos(2 * pi * frq.' * t), 1);
else
for idx = 1:lenFrq
start = 250 * (idx - 1) + 1; % Start index
stop = min(250 * idx, length(t)); % Stop index; ensure it does not exceed length(t)
if start <= length(t) && stop <= length(t)
mySig(start:stop) = cos(2 * pi * frq(idx) * t(start:stop));
end
end
end
The minor issue I’m experiencing is that, based on the selected sigType, the MATLAB code analyzer flags either the if block or the else block with a warning stating, "This statement (and possibly following ones) cannot be reached." It’s rather obvious that only one of the blocks will execute, and it seems redundant for the analyzer to flag this. I'm only asking this question because my OCD doesn't allow me to ignore that annoying little yellow warning ribbon.
Here's the photo to further clarify the issue:

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采纳的回答

Steven Lord
Steven Lord 2024-9-20
It’s rather obvious that only one of the blocks will execute, and it seems redundant for the analyzer to flag this.
In this circumstance, yes it is pretty clear to a human reading the code that only one of the blocks will execute. The line that defines which block will be executed occurs immediately before the if statement.
But in general it may not always be so obvious why MATLAB can prove to itself through static analysis that a line will not be executed, that it is dead code. So Code Analyzer will flag that scenario whenever it sees it.
If you know that the Code Analyzer message can safely be ignored, such as when you understand the scenario it's warning about and intended to use that behavior (like intentionally leaving off a semicolon to display a variable's contents), you can suppress it. See the "Adjust Code Analyzer Message Indicators and Messages" section on this documentation page.

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