Difference between #include <filename> and #include “filename”

Strangely, this isn’t really specified.

Most compilers, however, will only search for files in the first format (angle brackets) in the standard include paths.
They will search the source file’s directory first for files the second format (quotes), and then search the standard include paths.

Search Path – The C Preprocessor in the GCC online documentation
#include Directive (C/C++) in the Visual Studio documentation