I had something similar happen to me a while back, in my case me it was improper line endings that caused Clang Intellisense to see  bomb out. See this thread:

Clang Intellisense out of whack

I’ve also noticed it happen sometimes when there is a syntactical error somewhere in the code, such as a missing closing brace, but it is very rare.

Usually happens when windows CR LF line endings are not fixed by visual studio. Then intellisense gets out of whack

Just set VS 2015 ..etc to correct line endings or use a python scripts to do it automatically for all your files.

! /usr/bin/env python

<span style="color: #2a00ff;">"Replace LF with CRLF in argument files.  Print names of changed files."</span>

<span style="color: #7f0055;"><b>import</b></span> sys, re, os

def main():
    <span style="color: #7f0055;"><b>for</b></span> filename in sys.argv[1:]:
        <span style="color: #7f0055;"><b>if</b></span> os.path.isdir(filename):
            print filename, <span style="color: #2a00ff;">"Directory!"</span>
            <span style="color: #7f0055;"><b>continue</b></span>
        data = open(filename, <span style="color: #2a00ff;">"rb"</span>).read()
        <span style="color: #7f0055;"><b>if</b></span> <span style="color: #2a00ff;">'\0'</span> in data:
            print filename, <span style="color: #2a00ff;">"Binary!"</span>
            <span style="color: #7f0055;"><b>continue</b></span>
        newdata = re.sub(<span style="color: #2a00ff;">"\r?\n"</span>, <span style="color: #2a00ff;">"\r\n"</span>, data)
        <span style="color: #7f0055;"><b>if</b></span> newdata != data:
            print filename
            f = open(filename, <span style="color: #2a00ff;">"wb"</span>)
            f.write(newdata)
            f.close()

<span style="color: #7f0055;"><b>if</b></span> __name__ == <span style="color: #2a00ff;">'__main__'</span>:
    main()