Compiling C with gcc.
While
#include "/absolute/path/to/my/file"
works OK,
#include "../../relative/path/to/my/file"
fails with "no such file or directory". This only happens when the file is placed outside the project directory. file has read permissions. What could be the reason?
When using the format
#include "some_file.h"
the preprocessor by default looks in the same directory as the source file, if the file is not found there, it looks in the header-file search paths.
If the header file is not in the same directory as the source file, and not in one of the directories of the preprocessors search-path, then it will not be found.
You can write relative or full paths though:
#include "../some_directory/some_file.h"
Yes, you need GCC Options for Directory Search
When using gcc and local header files you need to add an include path to your build command.
mysource.c:
#include "localfile.h"
build command:
gcc -o program mysource.c
This works as long as the header file is in the same directory as your source (where you're running the command). If your header file is in a different directory you can include with the -I option:
gcc -I../headerdir -o hello.exe hello.c
or an absoulte path:
gcc -I/home/user/myprogra/headerdir -o hello.exe hello.c
Related
I have made a python "compiler" that helps me compile my C code with gcc, for example it fetches all my header files and source files. So my cmd commmand is gcc {headers} {source} -o {build_dir}/build.exe -lgdi32 -w where {headers} is a string like -Ipath/to/headers/foo.h -Ipath/to/other/headers.foo2.h and where {source} is the same but with .c files. It seems that the compiler finds the header files, but when compiling my code it fails.
(btw I am trying to make a portable programming environment on my flash drive so python and mingw are both portable)
This is the error: fatal error: test.h: No such file or directory #include "test.h"
My project tree
I have put the third party library files into the mingw directory instead of making a custom one and then linking it in the gcc command.
The -I option takes the path to the directory containing the header files or more specifically with an argument -Ipath and a directive #include<a/b.h>, the compiler will try to look for the header file at path/a/b.h.
So you should not give it paths to header files, only to the directory or directories relative to which you use include directives.
I am trying to compile a file Mv.c like - g++ microtime.c Mv.c
It gives an error - v.c:2:10: fatal error: microtime.h: No such file or directory 2 | #include <microtime.h>
My current directory has both microtime.h and microtime.c and Mv.c includes microtime.h
I am not sure how to go about compiling it.
Since my main program Mv.c is using microtime.h do I need to compile microtime.c first and pass it as an argument to g++?
I got it compiled by using the command g++ -I. Mv.c microtime.o
where microtime.o I generated using g++ -c microtime.c
I am not sure why this command works and why we need to specify the extra -I. option when I have already created the compiled object file microtime.o
If you write #include <microtime.h>, the compiler uses its list of system directories to look for the header file. By the option -I you add a directory to this list, and the compiler is happy.
To include project-local header files, use #include "microtime.h".
Read the chapter "Directory Options" in GCC's documentation to learn more.
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
$
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.
I work with C codes using gcc compiler and Clion IDE
So, I have a src folder for .c codes and include folder of .h files which contains a bunch of #define
I include some of the .h files in my main.c programe
when I run it in my Clion project, everything work fine
but when I try to run with command line (cuz I need command arguments), it says
Fatal Error: MyFunction.h, no such file or directory MyFunction.h IS MY FILE, NOT DEFAULT library file
What I typed in the command line is $gcc C:\Users\Admin\CLionProjects\project\src\main.c
What I get is "C:\Users\Admin\CLionProjects\project\src\main.c 10: Fatal Error: MyFunction.h No such file or directory.
Then I try to change the #include <MyFunction.h> to #include "MyFunction.h", hoping it will solve the problem, but no.
Then I did a test, I call a function of another .c file in the same src folder, and use command line to run main.c, but it tells me the function is not even defined.
cmd can recognized all the default library files like stdio.h, but none of those created by me. Any idea how to solve this problem? I know it must be some kind of path error
You have to tell gcc preprocessor where to find files you want to include.
You have two kinds of header:
System headers: included with #include <header>.
Local headers: included with #include "header".
Preprocessor searchs in header search path to find system headers.
Preprocessor searchs in current directory, then in header path to find local headers.
You can add folders in header search path using -I option in gcc invocation.
So in your case, you can compile with these commands:
$gcc -I C:\Users\Admin\CLionProjects\project\include C:\Users\Admin\CLionProjects\project\src\main.c
or
$cd C:\Users\Admin\CLionProjects\project\src
$gcc -I ..\include main.c
I am trying to include a library file named libmathematica.a in gcc so it gets linked in the executable example.
I attempt to do this with gcc main.c libmathematica.a -o example
Note: I have to do this with gcc, as ld won't link it properly with the correct system libraries
But I get: fatal error: mathematica.h: No such file or directory ,which is odd because mathematica.h is in the library.
Can you help?
A header file cannot be in the library. It has to be present at a certain location and you have to specify that location with the -I compiler flag:
gcc -I/path/to/mathematica/include main.c libmathematica.a -o example
If the header file is in the directory where the main.c is or in a subdirectory, then be sure that you use quotes and not angle brackets in the #include directive.
The issue would be in your source file. If the mathematica.h is in the system includes directory then you would use #include <mathematica.h> and if it was in some local directory then you would use something like #include "libs/mathematica.h".
Try adding to the gcc call - an option like
-I/Full/Path/To/The/Directory/Where/the/desired/header/resides
For example:
gcc -I/usr/include/mathematica -lmathematica -o example main.c