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What is the difference between #include <filename> and #include "filename"?
(30 answers)
Closed 7 years ago.
Here is a preprocessor directive in C :
#include <filename>
we can write it in this way also:
#include "filename"
Is there any difference between these two?
In general, the <> version should look only in "system directories", while the "" should look in the "local directories" first, and then the system directories.
What that actually means is implementation dependent. In most cases "" will look in the current directory first, but in some implementations it will look in the directory of the source (.c) file first (and some compilers have a switch for that). Also, behavior is different w.r.t. the "set of system directories" to search if "local directory search" fails (the same as for <> or not).
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This question already has answers here:
What is the difference between #include <filename> and #include "filename"?
(30 answers)
Closed 4 months ago.
I'm really new to programming just started last week, and i have a problem where my c-file doesn't recognize the cs50.h file when it's in the same folder as my program. i have msys2 installed.
I don't know how to proceed.
Using <header_here.h> takes them from some system wide directory (not sure for windows but for linux it is /usr/include/
that has these header files.
For the current path use #include "headername_here.h" instead.
#include "cs50.h"
This question already has answers here:
What tokens are permitted as arguments to #include?
(2 answers)
Closed 2 years ago.
can someone explain to me why writing something like:
#include "file.txt"
#include "File.js" /* why including files other than files with .h extension is valid */
#include "anotherFile.c"
main()
{
printf("why including files other than header files (.h files) is allowed in C");
}
So can someone provide me a good tutorial online describing this. when i search online about this i find nothing. is this behavior of #include directive described somewhere in the C standard pdf or C standard html if so please guide me to the actual page where this behavior is described in the C standard with a link
The include directive is part of the C Preprocessor. The preprocessor will simply replace an include with the contents of the file referenced.
See 6.10.2 Source file inclusion:
A preprocessing directive of the form
#include "q-char-sequence" new-line causes the replacement of that directive by the entire contents of the source file identified by the
specified sequence between the " delimiters.
This question already has answers here:
What is the difference between #include <filename> and #include "filename"?
(30 answers)
Difference between angle bracket < > and double quotes " " while including header files in C++? [duplicate]
(2 answers)
Closed 9 years ago.
I would like an explanation of the difference between < header.h > and "header.h" in library #include directives. How exactly (in which locations) does the linker search for the files? In what order does it perform the search?
When we write <stdio.h> , we are referring to a header file which is available in the include directory of the system. When we write #include <stdio.h>, the preprocessor searches for the header file in the system include directory and not in the current directory. When we write #include "stdio.h", the preprocessor starts searching for this header file in the current directory and then in its parent directories. So if we write our own stdio.h, save it in the current directory, and include it in the program using #include "stdio.h" then our header will be included instead of the system header.
In short, if we use angular brackets (<>) then we are indicating that the file can be found in one if the standard directories in the
system. If we use quotation marks (" ") then we are indicating that a non-standard header is being used.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
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..
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 ...
The <> usually denotes System headers and the "" usually denote header files in the current directory (usually your header files). Source/Reference here for more info:
Difference between angle bracket < > and double quotes " " while including header files in C++?
My understanding was always that by doing #include <header.h> it looks in the system include directories, and that #include "header.h" it looks in the local directory. But I was just looking at the python source code and it uses the "header.h" method to define headers in a sibling directory.
So in py3k/Python/ast.c it does #include "Python.h". But Python.h is in py3k/Include/Python.h
Is this something common that I've just never seen, not having worked on any real large C project? How do I tell, at least my IDE, to look in py3k/Include?
Update
I figured out how to tell my IDE to include them, it was just me being stupid and a spelling error. But I'm more interested in why "" works. Is that not the different between "" and <>?
Both #include <header> and #include "header" look in "implementation-defined places", i.e. it depends on the compiler you are using and its settings. For #include <h> it's usually some standard system include directories and whatever you configure the compiler to look in additionally.
The difference between the two versions is that if the search for #include "header" is not supported or fails, it will be reprocessed "as if it read #include <header>" (C99, §6.10.2).
You need to somehow tell your compiler what directories to search in -- for GCC this means using the -I flag. Look it up for your combination of IDE / compiler.