694: Mainline

Note that, when a header file specification is surrounded by angle brackets <...>, the C++ compiler first looks for that header file in a directory known by your C++ compiler to contain header files for the standard library. Later on, when the C++ compiler needs the object code corresponding to the function prototypes in a header file, it looks for that object code in a directory known to contain the standard library file.

In contrast, when the file specification is surrounded by double-quotation marks, "...", the C++ compiler first looks for the header file in the current directory—which is presumably the same one that contains the source-code file.

Whenever the first look produces no header file, most compilers look elsewhere. For file specifications with angle brackets, the second look is likely to be the current directory; for file specifications with double-quotation marks, the second look is likely to be the standard library's directory.

Many compilers also allow you to specify additional places to look by way of a command line argument.