Question

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What is the difference between #include <filename> and #include “filename”?

I just got involved into a project.

When I were tracing the project code, I found that

some people can include a header file by this way:

include < XXX.h >

XXX.h is a header file that is not in system libraries and made by our own programmers…

My question is how to use ‘<‘ and ‘>’ instead of double ” ?

and how to include headers in other directories by this way?

for example:

headers/header_a.h
headers/header_b.h

I can use include < header_a.h > and < header_b.h >…

should I use Makefile to implement this? thanks..

Answer 1

A file in double-quotes is referenced relative to the current directory:

#include "../file.h" // file from parent directory

You’d generally use this for your own headers.

A file in angle-brackets is referenced relative to the paths specified to the compiler:

#include <sys/bits.h> // file under, e.g.,  /usr/include
#include <thirdpartytools/somelib.h> // file under /path/to/third/party/includes

You’d generally use this for system or perhaps third-party headers, assuming the compiler is invoked with something like

gcc -I/usr/include -I/path/to/third/party/includes ...