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
Related
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.
I'm try to compile a .c file from the terminal using gcc. The file includes a personal library where a function is defined. This library.h and the .c file are in the same directory.
I get the following message error
undefined reference to `function'"
Should I use another argument as:
gcc -o nameoutput filename
or should I place the library.h in another directory?
Assuming you have library.c, library.h and main.c in your current working directory:
$ gcc -Wall main.c library.c -o my_program
and then to run it:
$ ./my_program
"Undefined reference" means that the linker can't find the object file containing the compiled body of function; it doesn't have anything to do with the .h file.
I sounds like you have a situation where library.h and library.c are in one directory, and main.c is in a different directory. If that's the case, then your command line will need to look something like this:
gcc -o program -I /path/to/library main.c /path/to/library/library.c
-I /path/to/library means that gcc will look for .h files in that path as well as the standard include paths. That also allows you to write
#include "library.h"
instead of
#include "/path/to/library/library.h"
in any code that needs it.
I have made a header and a source but I don't know how to link them up. I looked it up on the web but the commands provided didn't work (or I wouldn't be here :) ).
To compile it (if you use GCC):
Header:
$ gcc -c whatever.h -o whatever.o
Source:
$ gcc -c sample.c -o sample.o
To link the files to create an executable file:
$ gcc sample.o whatever.o -o sample
What did I do wrong. I am using geany for writing (compile error is here) but the commands are executed on a terminal in the same directory. can anybody give me the build commands for geany so whenever I want to include a header I can just compile and run?
Good and the right way would be to
sample.c
#include "header.h"
and compile
gcc sample.c -o ob
Thumb Rule:
header files [.h] are for #includeing
source files [.c] are for compiling and linking together to create the executable.
Once you've #included your header file in a .c file, there's no need to compile the header file and produce an object file.
FYI, you can check the effect of #include-ing the header file by running
gcc -E sample.c
and hope you'll understand why you need not compile and link the header file separately.
EDIT:
if you have a sample.c and whatever.h, to produce and run the binary, simply do
#include "whatever.h" in the top of sample.c
gcc -o sample sample.c
./sample
if you include header file by:
#include <header.h>
it will give this error.
Instead you can write as given below:
#include "header.h"
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
I want to compile a small program which has a pretty straight forward makefile, but I seem unable to get it working. Maybe you can help me. The makefile has the following targets:
visca-cli: visca-cli.c libvisca_hl.o
gcc -Wall -o visca-cli visca-cli.c /usr/local/lib/libvisca.so libvisca_hl.o
libvisca_hl.o: libvisca_hl.c
gcc -Wall -c libvisca_hl.c
I can 'make libvisca_hl.o' successfully and create the .o file. But 'make visca-cli' fails with error messages like
libvisca_hl.c:(.text+0x468a): undefined reference to
`VISCA_get_md_disptime'
for every single function defined in libvisca.h (here it's VISCA_get_md_disptime)
Here are the include sections from the various files (ommitting standard libraries):
In visca-cli.c:
#include "libvisca.h"
#include "libvisca_hl.h"
In libvisca_hl.c:
#include "libvisca_hl.h"
In libvisca_hl.h:
#include "libvisca.h"
All includes quoted with "" are present in the local directory where I run make and where all the sourcefiles are. There are no subfolders. So I guess the problem lies with the makefile? Any help appreciated!
The order of libraries and objects on your compilation/link command line matters. In your case, you just need to put the shared object at the end:
gcc -Wall -o visca-cli visca-cli.c libvisca_hl.o /usr/local/lib/libvisca.so
On most systems /usr/local/lib is already part of the standard library search path, so you could simplify further:
gcc -Wall -o visca-cli visca-cli.c libvisca_hl.o -lvisca