The two references you will likely use most often are cplusplus.com and cppreference.com. Both are excellent references to the standard C and C++ libraries.
Kernighan, Brian, and Dennis Ritchie. The C Programming Language. Prentice, 1990. ISBN: 9788120305960.
- Known as "K. and R." This is the original book on C and writen by its creator. However it's quite old, so it does not cover C99.
Stroustrop, Bjarne. The C++ Programming Language. 4th ed. Addison-Wesley Professional, 2013. ISBN: 9780321563842.
Bjarne Stroustrop is the creator and eternal guru of C++; the 4th edition is very recently updated for C++11, so this is an excellent resource.
Meyers, Scott. Effective C++: 55 Specefic Ways To Improve Your Programs And Designs. Addison-Wesley Professional, 2005. ISBN: 9780321334879. [Preview with Google Books]
———. More Effective C++: 35 New Ways To Improve Your Programs And Designs. Addison-Wesley Professional, 1996. ISBN: 9780201633719. [Preview with Google Books]
———. Effective STL: 50 Specific Ways to Improve Your Use of Standard Template Library. Addison-Wesley Professional, 2001. ISBN: 9780201749625.
Other Web References