For the first question:
The C++ standard explicitly lists the C standard(s) on which it depends in its Normative references section. For C++14, [intro.refs] 1.2/1 happens to list C 99:
- ISO/IEC 9899:1999, Programming languages — C
- ISO/IEC 9899:1999/Cor.1:2001(E), Programming languages — C, Technical Corrigendum 1
- ISO/IEC 9899:1999/Cor.2:2004(E), Programming languages — C, Technical Corrigendum 2
- ISO/IEC 9899:1999/Cor.3:2007(E), Programming languages — C, Technical Corrigendum 3
For the second question:
The C++ standard does not implicitly incorporate any parts of the C standard; all references to the C standard are explicit. A good source of information on where C++ deviates from C is Annex C, “Compatibility” of the C++ standard, particularly C.1 [diff.iso].
Additionally, references to the C standard library are scattered throughout the description of the C++ standard library (chapters 17–30 in C++14). Of particular interest can be:
- 17.2 [library.c], which describes the basic inclusion of the C standard library
- Chapter 18 [language.support], which describes many of the
<c:::>headers of the C++ standard library (those which offer the C standard library functionality).