使用opencv_haartraining训练，如果出现异常：
Assertion failed (elements_read == 1) in icvGetHaarTraininDataFromVecCallback, file C:\build\2_4_winpack-build-win64-vc14\opencv\apps\haartraining\cvhaartraining.cpp, line 1861
根据异常名字icvGetHaarTraininDataFromVecCallback可知是从vec文件提取数据失败
把npos和nneg数量设置小一点，如果没有用，就把之前成功时生成的xml文件和文件夹删除掉。
Assertion failed (elements_read == 1) in icvGetHaarTraininDataFromVecCallback
原文：https://www.cnblogs.com/XT-xutao/p/13124975.html