How to avoid clang-tidy warnings about uninitialized variables

Question

I am looking for the best way to avoid cppcoreguidelines-init-variables warnings with clang-tidy.

std::istringstream in(line);
float x, y, z, rotx, roty, rotz;
in >> x >> y >> z >> rotx >> roty >> rotz;

-> variable 'x' is not initialized, variable 'y' is not initialized, ...

double min_intensity, max_intensity;    
cv::Point point_min, point_max;
cv::minMaxLoc(input, &min_intensity, &max_intensity, &point_min, &point_max, elliptic_mask_around_center);

-> variable 'min_intensity' is not initialized, ...

I could assign a value for x, y, ... and min_intensity and max_intensity, but I do not see why I should do it.

What would be the best way to avoid this warning?

float x = 0.F; // initialize to a value, but 6 lines, and it makes no sense because x is never 0
float x = NAN; // works but 6 lines, and needs <cmath> inclusion
float x, y, z, rotx, roty, rotz; // NOLINT [not very practical, and means the warning is a false positive]

Thank you for your help.

Answer 1

In general you should initialize variables always because reading from an uninitialized variable is undefined behavior.

When extraction from the stream fails then since C++11 a 0 is assigned. However, this is only the case as long as the stream is not in a fail state. Hence, when reading x fails then x will have a value of 0 but the others will have an indetermindate value.

You should always check if extraction succeded:

if (in >> x >> y >> z >> rotx >> roty >> rotz) { 
     // use x,y,z,rotx,roty,rotz
}

And if you want to use part of the input even in case extraction fails at some point, you should read them seperately:

if (in >> x) {
     // use x
}
if (in >> y) {
     // use y
}
// ...

If you do that, the initialization is strictly speaking not necessary. However, reading from a stream is way more expensive than initializing a variable, so to be consistent (see eg here) I would suggest to initialize them anyhow. Don't worry about more lines of code, a common recommendation is to declare a single variable per line anyhow (see eg here):

std::istringstream in(line);
float x = 0.0;
float y = 0.0;
float rotx = 0.0;
float roty = 0.0;
float rotz = 0.0;
if (in >> x >> y >> z >> rotx >> roty >> rotz) {
     // extraction succeeded
} else {
     // extraction failed
}