it was a problem with my Include directories in VisualGDB Properties–>Makefile settings. I was adding a new directory for each library I got. I reinstalled VS2015, but that did nothing because the culprit was a project option. I copied the default* include directories and that was it.
*someone on my team provided me with a list of the default include directories
solved ‘strtoll’ and many others “not a member of ‘std'”