CODEWITHSUNDEEP
cgcc
Tim
Tim

Reputation: 99428

Does `#include "FILE.h"` make gcc search for FILE.h in the current directory or somewhere else?

An Introduction to GCC by Brian Gough says

Incidentally, the difference between the two forms of the include state- ment #include "FILE.h" and #include <FILE.h> is that the former searches for FILE.h in the current directory before looking in the system header file directories. The include statement #include <FILE.h> searches the system header files, but does not look in the current directory by default.

But the following example seems to imply the directory containing the source file being compiled, instead of the current directory. What is correct?

$ mv src/hello.h .
$ gcc  -c src/main.c
src/main.c:1:10: fatal error: hello.h: No such file or directory
 #include "hello.h"
          ^~~~~~~~~
compilation terminated.
$ mv hello.h src/
$ gcc  -c src/main.c
$

Upvotes: 1

Views: 735

Answers (1)

zwol
zwol

Reputation: 140629

https://gcc.gnu.org/onlinedocs/cpp/Search-Path.html states that

By default, the preprocessor looks for header files included by the quote form of the directive #include "file" first relative to the directory of the current file, and then in a preconfigured list of standard system directories. For example, if /usr/include/sys/stat.h contains #include "types.h", GCC looks for types.h first in /usr/include/sys, then in its usual search path.

For the angle-bracket form #include <file>, the preprocessor’s default behavior is to look only in the standard system directories.

The document you are reading is therefore incorrect. Perhaps Mr. Gough has never attempted to write a nonrecursive Makefile, or separate his source and object directories, and has therefore never noticed that "the current directory" and "the directory containing the current file" are not necessarily the same thing.

GCC has a whole bunch of command line options that you can use to reconfigure how #include works. There is even an option that turns off looking in the directory of the current file (-I-), but it is not usable on many operating systems because it will break the C library's headers.

Upvotes: 2

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