3 things need to be taken care of in this case:

• use the current HEAD because the 2.1 release has an issue regarding this "feature"
• configure your project with the cmake command line option -DBUILD_EXPERIMENTAL_API=ON
• modify the BarcodeReader.cpp by adding the line hints.setTryDenoise(true);

Thanks, I tried removing BUILD_EXPERIMENTAL_API check from the code and also turned ON the flag in CMakeList files. The tryDenoise hint does make a difference in detection speed and quality.

But even this is not able to detect codes with some impurities.
Case : Sometimes QR codes need to be printed on invoices, tickets, etc. having a pre-printed template like lines or blocks. These codes can get overlapped with these template items (like one of the sample here)

This red line has nothing to do with 'noise'. It simply destroys 2 of 3 finder patterns and they are the features that make QRCodes recognizable as such. This image is not decodeable with zxing-cpp and will unlikely be anytime soon. My advice: don't break your symbol by printing random lines over them.