Is there a clean way to differentiate debian include path from RH/fedora/centos one?
I'd like to link with the wbxml2 library but unfortunately the include file si not in the same location depending of the distro.
on debian/ubuntu:
#include <wbxml.h>
and on others:
#include <wbxml2/wbxml.h>
Does anybody have a clean solution to make this code portable (using #ifdef for example) ?
Thanks
Looking at the list of provided files for the -dev package shows, among other things of course:
/usr/lib/pkgconfig/libwbxml2.pc
That line is a "package configuration" file for the development package. That means you don't need to care about the absolute location: use the package configuration tool instead.
Add this to your Makefile:
CFLAGS += $(pkg-config --cflags libwbxml2)
LDLIBS += $(pkg-config --libs libwbxml2)
And you will get the proper paths on all systems using pkg-config.
This is the proper, correct and expected way to deal with this issue, and the reason pkg-config exists in the first place.
Related
The program is to run a c program to parse a xml file in windows Gcc mingw.
but on compilation i get xml2-config not found ,--libs unrecognized commands, --cflags unrecognized commands.
gcc
i have added libxml files "libxml libxslt iconv" to the environmental path.
When you write a program that uses a third-party library like libxml, typically you have two problems:
You need to tell the compiler where the library's header files are installed, so that when your code says things like #include <xml.h> the compiler will be able to find them.
You need to tell the linker where the library itself is installed.
If you don't manage to do step 1 correctly, you typically get an error like "error: 'xml.h' file not found".
If you don't manage to do step 2 correctly, you typically get errors like "Undefined symbol: _xmlparse" or "library not found for -llibxml". ("Undefined symbol" means the compiler didn't even know to look for the library, so it complains that there are no definitions for the functions that would have been found in it. "library not found for -llibxml" means you told the compiler which library to look for, but it couldn't find it.)
On C compilers under Unix, anyway, you tell the compiler where to look for header files using the -I flag, like this:
cc -Idirectory_where_extra_header_files_are -c test.c
You tell the compiler/linker to load an additional library using the -l flag:
cc test.o -llibxml
You tell the compiler/linker where to find that additional library using the -L flag:
cc test.o -Ldirectory_where_extra_library_files_are -llibxml
But this can be a nuisance. Many third-party libraries come with "config" programs which are supposed to help you with this. An invocation like
xml-config --cflags
prints the string
-Idirectory_where_the_libxml_header_files_are
so you know what to add to the cc line to fix problem 1. And the an invocation like
xml-config --libs
prints the string
-Ldirectory_where_the_libxml_libraries_are -llibxml
so you know what to add to the cc line to fix problem 2.
And then, finally, this tool is intended to be used a special mechanism of the Unix shell, the backquote, which lets you take the output of one command and insert it into another command line:
cc `xml-config --cflags --libs` test.c
This literally runs the xml-config command, collects its output (that is, whatever xml-config prints out), and inserts that input into the command line, just as if you'd typed it, and then finally runs the cc command with those additional arguments. It's a handy mechanism, but if you're using Windows you may not be able to use it.
So if you're on a Unix-like system and if the xml-config program is installed where the shell can find it and if the header files and libraries are installed where xml-config thinks they are, then using xml-config can be very convenient. But if any of these things is not true, the whole mechanism breaks down, and you may have to do things "by hand".
Doing things "by hand" isn't impossible, and it isn't even particularly difficult. It's how we always did things back before this kind of "config" tool helper mechanism was invented. As discussed above, just use -I to tell the compiler where the header files are when you compile:
cc -Idirectory_where_the_libxml_header_files_are -c test.c
Use -L and -l to tell it where the library is:
cc test.o -Ldirectory_where_the_libxml_libraries_are -llibxml
I installed all the libmagick-dev packages (magickwand, magick++, etc) in Ubuntu 16.04 but I don't know where is the library... So I haven't included it to my C program.
I need to use the pixel level functions for a project I'm developing
When typing 'locate libmagick', I just get the /usr/share/doc stuff.
It's the docs, not the libraries.
I need to include the .h files to my program so I can manipulate images.
At the moment, I'm making tests for the image manipulations (simple programs that are in the imagemagick.org site wich use the magickwand API)...
But that's a thing I don't know how to do...
Where's the library?
That's a first step :(
Installed -dev Packages:
libmagick++-6.q16-dev (imagemagick C++ developer API)
libmagickcore-6.q16-dev (magickcore low-access API for C)
libmagickcore-6-headers
libmagickwand-6.q16-dev (magickwand C developer API)
libmagickwand-6-headers
I also installed the libmagickwand-dev package, though apt says it's a transitional package that could be removed...
I've read that those packages would be enough, but it seems it's not...
Thanks for your replies ;-)
On a Ubuntu/Debian system, the libraries are usually under /usr/lib, or a subdirectory managed by the package installer + system architecture.
You can find them with...
find /usr/lib -name 'libMagick*'
The actual location is not terribly important as you should be leveraging pkg-config, or MagickWand-config utility for the required CC + LD flags.
For example
pkg-config --cflags --libs MagickWand
#=> -fopenmp -I/usr/include/ImageMagick -lMagickWand -lMagickCore
or
MagickWand-config --cflags --libs
#=> -fopenmp -I/usr/include/ImageMagick
# -lMagickWand -lMagickCore
So a simple MagickWand test can be something like...
// test.c (creates a single rose.bmp image for testing)
#include <wand/MagickWand.h>
int main()
{
MagickWandGenesis();
MagickWand *test = NewMagickWand();
MagickReadImage(test, "rose:");
MagickWriteImage(test, "rose.bmp");
DestroyMagickWand(test);
MagickWandTerminus();
return 0;
}
And can be compiled with..
cc -o make_rose_image $(pkg-config --cflags --libs MagickWand) test.c
What I had to do was installing the libmagick-dev libraries. They were at /usr/lib.
When typing find /usr/lib -name 'libMagick*', got
/usr/lib/x86_64-linux-gnu/libMagick++-6.Q16.a
/usr/lib/x86_64-linux-gnu/libMagick++-6.Q16.so
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2.0.0
/usr/lib/x86_64-linux-gnu/libMagickWand-6.Q16.so
/usr/lib/x86_64-linux-gnu/libMagickWand-6.Q16.a
/usr/lib/x86_64-linux-gnu/libMagick++-6.Q16.la
/usr/lib/x86_64-linux-gnu/libMagick++-6.Q16.so.5.0.0
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so
/usr/lib/x86_64-linux-gnu/libMagick++-6.Q16.so.5
/usr/lib/x86_64-linux-gnu/libMagickWand-6.Q16.so.2
/usr/lib/x86_64-linux-gnu/libMagickWand-6.Q16.so.2.0.0
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.a
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.la
/usr/lib/x86_64-linux-gnu/libMagickWand-6.Q16.la
And there they are!
The libraries are in /usr/lib
And a program who uses MagickWand is called by
cc -o output $(pkg-config --cflags --libs MagickWand) source.c
:)
I am trying to compile a C program that requires Image Magick's MagickWand.h:
#include "wand/MagickWand.h"
But my Image Magick was installed through Homebrew on my Mac so I changed the include to the actual location:
#include </usr/local/Cellar/imagemagick/6.8.9-7/include/ImageMagick-6/wand/MagickWand.h>
However, when I compiled the program I received the following error:
/usr/local/Cellar/imagemagick/6.8.9-7/include/ImageMagick-6/wand/MagickWand.h:71:10: fatal error: 'wand/method-attribute.h' file not found
#include "wand/method-attribute.h"
Now I've been going into the .h files when this error crops up and changing their #includes so that they are pointed correctly (because that appears to be the problem), but there is always a new error here and I'd rather not spend hours manually updating these because of a Homebrew install. Does anyone have any suggestions on how to fix this without manually updating each file? I'm not sure exactly what the problem is so perhaps there is a more elegant solution.
Your code should include the MagickWand library as system headers, and keep the generic path. This will keep your future compiling from breaking when the system/library updates.
#include <wand/MagickWand.h>
Tell your C compiler where homebrew installed ImageMagick by setting the preprocessor include flag -I, and linking/library options with the -L & -l flags.
example:
clang -I/usr/local/Cellar/imagemagick/6.8.9-7/include/ImageMagick-6 \
myProject.c -o myProject.o \
-L/usr/local/Cellar/imagemagick/6.8.9-7/lib \
-lMagickWand-6.Q16 \
-lMagickCore-6.Q1
To simplify the whole process, ImageMagick ships MagickWand-config utility. This will take care of libs, includes, and definitions for you.
example:
CFLAGS=$(MagickWand-config --cflags)
LFLAGS=$(MagickWand-config --libs)
clang $CFLAGS myProject.c -o myProject.o $LFLAGS
I have a sample C project that use GLib Library. In that source code, it use :
#include <glib.h>
When I compile, I found this error : "Glib.h : no such file or folder". I have google and find out that I should install this lib. So I use those command:
apt-get install libgtk2.0-dev
apt-get install glade
After that, I have checked and see already exist this header file in my system: usr/include/glib-2.0/glib.h But when I compile, I still meet problem above.
So I have change include line to :
#include <glib-2.0/glib.h>
So, after that, when I compile, I meet error inside glib.h header :
#ifndef __G_LIB_H__
#define __G_LIB_H__
#define __GLIB_H_INSIDE__
#include <glib/galloca.h>
#include <glib/garray.h>
// more code here
glib/galloca.h : no such file or directory. Because this error is inside system header file, I cannot modify anymore and still cannot compile.
I don't know how to fix this. I have read some post, that they change makefile. But, because my project is compiled automatically by IDE (CodeBlock) and I cannot really write a makefile, so that method doesn't suitable for me.
Please tell me a way to fix this.
Thanks :)
There must be some problem with how you build. To compile C programs that use GLib, you need package libglib2.0-dev. You can either install it directly, or install libgtk2.0-dev, which pulls it in as a dependency. So you have the packages you need.
The correct way to compile a GLib program is to use -I with the path to the GLib include files.
An example (from How to compile a helloworld GLib program? on askubuntu):
gcc $(pkg-config --cflags --libs glib-2.0) hello_glib.c
This should let you compile this program:
#include <stdio.h>
#include <glib.h>
int main(int argc, char** argv) {
GList* list = NULL;
list = g_list_append(list, "Hello world!");
printf("The first item is '%s'\n", g_list_first(list)->data);
return 0;
}
The errors you are getting indicate that you are not setting the include path (-I) correctly. How to do this depends on your build system/IDE.
In Code::Blocks, you must set the include path and the linker options in the appropriate configuration dialog. Run pkg-config --cflags --libs glib-2.0, which will output something like
-I/usr/include/glib-2.0 -I/usr/lib/i386-linux-gnu/glib-2.0/include -lglib-2.0
The directories after -I must be set in the compiler options of your project (should be under Project -> Build Options -> Search Directories), and the names after -l must be set in the linker settings. Another option is to create a Makefile, and let Code::Blocks use that.
See e.g. Q: What do I need to know when using 3rd party libs? in the Code::Blocks Wiki.
You should not alter your source code (e.g. the #include directives).
You just need to use pkg-config (both for compiling, with --cflags, and for linking, with --libs), preferably with a builder program like make.
This is an example for exactly your situation: a Makefile using pkg-config to compile some source program using glib
I'm attempting to use a C library for an opencourseware course from Harvard. The instructor's instructions for setting up the external lib can be found here.
I am following the instructions specific to ubuntu as I am trying to use this lib on my ubuntu box. I followed the instructions on the page to set it up, but when I run a simple helloWorld.c program using a cs50 library function, gcc doesn't want to play along.
Example:
helloWorld.c
#include <stdio.h>
#include <cs50.h>
int
main(void){
printf("What do you want to say to the world?\n");
string message = GetString();
printf("%s!\n\n", message);
}
$ gcc helloWorld.c
/tmp/ccYilBgA.o: In function `main':
helloWorld.c:(.text+0x16): undefined reference to `GetString'
collect2: ld returned 1 exit status
I followed the instructions to the letter as stated in the instructions, but they didn't work for me. I'm runing ubuntu 12.04. Please let me know if I can clarify further my problem.
First, as a beginner, you should always ask GCC to compile with all warnings and debugging information enabled, i.e. gcc -Wall -g. But at some time read How to invoke gcc. Use a good source code editor (such as GNU emacs or vim or gedit, etc...) to edit your C source code, but be able to compile your program on the command line (so don't always use a sophisticated IDE hiding important compilation details from you).
Then you are probably missing some Harvard specific library, some options like -L followed by a library directory, then -l glued to the library name. So you might need gcc -Wall -g -lcs50 (replace cs50 by the appropriate name) and you might need some -Lsome-dir
Notice that the order of program arguments to gcc is significant. As a general rule, if a depends upon b you should put a before b; more specifically I suggest
Start with the gcc program name; add the C standard level eg -std=c99 if wanted
Put compiler warning, debugging (or optimizing) options, eg -Wall -g (you may even want to add -Wextra to get even more warnings).
Put the preprocessor's defines and include directory e.g. -DONE=1 and -Imy-include-dir/
Put your C source file hello.c
Put any object files with which you are linking i.e. bar.o
Put the library directories -Lmy-lib-dir/ if relevant
Pur the library names -laa and -lbb (when the libaa.so depends upon libbb.so, in that order)
End with -o your-program-name to give the name of the produced binary. Don't use the default name a.out
Directory giving options -I (for preprocessor includes) and -L for libraries can be given several times, order is significant (search order).
Very quickly you'll want to use build automation tools like GNU make (perhaps with the help of remake on Linux)
Learn also to use the debugger gdb.
Get the habit to always ask for warnings from the compiler, and always improve your program till you get no warnings: the compiler is your friend, it is helping you!
Read also How to debug small programs and the famous SICP (which teaches very important concepts; you might want to use guile on Linux while reading it, see http://norvig.com/21-days.html for more). Be also aware of tools like valgrind
Have fun.
I take this course and sometimes I need to practice offline while I am traveling or commuting. Under Windows using MinGW and Notepad++ as an IDE (because I love it and use it usually while codding python) I finally found a solution and some time to write it down.
Starting from scratch. Steps for setting up gcc C compiler, if already set please skip to 5
Download Git and install. It includes Git Bash, which is MINGW64 linux terminal. I prefer to use Git as I need linux tools such as sed, awk, pull, push on my Windows and can replace Guthub's terminal.
Once Git installed make sure that gcc packages are installed. You can use my configuration for reference...
Make sure your compiler works. Throw it this simple code,
by saving it in your working directory Documents/Harvard_CS50/Week2/
hello.c
#include <stdio.h>
int main(void)
{
printf("Hello StackOverflow\n");
}
start Git Bash -> navigate to working directory
cd Documents/Harvard_CS50/Week2/
compile it in bash terminal
gcc helloworld.c -o helloworld.exe
execute it using bash terminal
./helloworld.exe
Hello StackOverflow
If you see Hello StackOverflow, your compiler works and you can write C code.
Now to the important bit, installing CS50 library locally and using it offline. This should be applicable for any other libraries introduced later in the course.
Download latest source code file cs50.c and header file cs50.h from https://github.com/cs50/libcs50/tree/develop/src and save them in Documents/Harvard_CS50/src
Navigate into src directory and list the files to make sure you are on the right location using
ls
cs50.c cs50.h
Cool, we are here. Now we need to compile object file for the library using
gcc -c -ggdb -std=c99 cs50.c -o cs50.o
Now using the generated cs50.o object file we can create our cs50 library archive file.
ar rcs libcs50.a cs50.o
After all this steps we ended with 2 additional files to our original files. We are interested in only 2 of them cs50.h libcs50.a
ls
cs50.c cs50.h cs50.o libcs50.a
Copy Library and header files to their target locations. My MinGW is installed in C:\ so I copy them there
cs50.h --> C:\MinGW\include
libcs50.a --> C:\MinGW\lib
Testing the cs50 Library
To make sure our library works, we can throw one of the example scripts in the lecture and see if we can compile it using cs50.h header file for the get_string() method.
#include <stdio.h>
#include <cs50.h>
int main(void)
{
printf("Please input a string to count how long it is: ");
string s = get_string();
int n = 0;
while (s[n] != '\0')
{
n++;
}
printf("Your string is %i chars long\n", n);
}
Compile cs50 code using gcc and cs50 library. I want to be explicit and use:
gcc -ggdb -std=c99 -Wall -Werror test.c -lcs50 -o test.exe
But you can simply point the source, output filename and cs50 library
gcc test.c -o test.exe -lcs50
Here we go, program is compiled using header and methods can be used within.
If you want Notepad++ as an IDE you can follow this tip to set it up with gcc as a compiler and run your code from there.
Just make sure your nppexec script includes the cs50 library
npp_save
gcc -ggdb -std=c99 -Wall -Werror "$(FULL_CURRENT_PATH)" -lcs50 -o "$(CURRENT_DIRECTORY)\$(NAME_PART).exe"
cmd /c "$(CURRENT_DIRECTORY)\$(NAME_PART).exe"
Download the cs50 from: http://mirror.cs50.net/library50/c/library50-c-5.zip
Extract it. (You will get two files cs50.c and cs50.h)
Now copy both the files to your default library folder. (which includes your stdio.h file)
Now while writing your program use: #include < cs50.c >
You can also copy the files to the folder containing your helloWorld.c file.
You have to use: #include " cs50.c ".
OR =====================================================================>
Open cs50.c and cs50.h files in text editor.
In cs50.h, just below #include < stdlib.h > add #include < stdio.h > and #include < string.h > both on new line.
Now open cs50.c file, copy everything (from: /**Reads a line of text from standard input and returns the equivalent {from line 47 to last}) and paste it in cs50.h just above the #endif and save the files.
Now you can copy the file cs50.h to either your default library folder or to your current working folder.
If you copied the file to default folder then use: #include < cs50.h > and if you copied the files to current working folder then use: #include " cs50.h ".
You need to link against the library during compilation. The library should end in .a or .so if you are on Ubuntu. To link against a library:
gcc -o myProgram myProgram.c -l(library name goes here but no parentheses)
You have to link against the library, how come GCC would know what library you want to use?
gcc helloWorld.c -lcs50
Research Sources:
building on the answers above given by Basile Starynkevitch, and Gunay Anach
combined with instructions from some videos on youtube 1 2
Approach:
covering the minimum things to do, and sharing the "norms" separately
avoiding any modification to anywhere else on the system
including the basic breakdown of the commands used
not including all the fine details, covering only the requirements absolute to task or for effective communication of instructions. leaving the other mundane details to the reader
assuming that the other stuff like compiler, environment variable etc is already setup, and familiarity with shell's file navigation commands is there
My Environment:
compiler: gcc via msys2
shell: bash via msys2
IDE: doesnt matter here
Plan:
getting the source files
building the required files: *.o (object) and *.a (archive)
telling the compiler to use it
Action:
Let's say, current directory = "desktop/cs50"
It contains all the *.c files like test-file.c which I will be creating for assignments/problem sets/practise etc.
Get the *.h and *.c files
Source in this particular case: https://github.com/cs50/libcs50/tree/main/src
Go over each file individually
Copy all the content of it
Say using "Copy raw contents" icon of individual files
Create the corresponding file locally in the computer
Do it in a a separate folder just to keep things clean, let's say in "desktop/cs50/src" aka ./src
Build the required files using in the terminal after changing your current directory to "desktop/cs50/src" :
gcc -c cs50.c to create the "cs50.o" object file from "cs50.c" using "gcc"
ar cr libcs50.a cs50.o to create "libcs50.a" archive file which'll be containing "cs50.o" object file
Here, "libcs50" = "lib" prefix + "cs50" name (same as the header file's name)
This is the norm/standard way where the prefix "lib" is significant as well for a later step
However, prefix can be skipped, and it's not compulsory for name to match the header file's name either. Though, Skipping prefix is not recommended. And I can't say for sure about the name part
To tell the compiler to be able to use this infrastructure, the commands will be in following syntax after going to the parent directory (i.e. to "desktop/cs50"):
gcc test-file.c -Isrc -Lsrc -lcs50 if you used "lib" prefix in step 2.2 above
here, -I flag is for specifying the directory of *.h header file included in your test_file.c
and -L flag is for specifying the directory to be used for -l
and -l is for the name of the *.a file. Here the "lib" prefix talked about earlier, and ".a" extension is not mentioned
the order of these flags matter, keep the -I -L -l flags after the "test-file.c"
Some more notees:
don't forget to use the additional common flags (like those suggested above for errors etc)
if you skipped the "lib" prefix, then you can't use -L -l flags
so, syntax for command will become: gcc test-file.c -Isrc src/libcs50.a
say i created my test-file.c file in "desktop/cs50/psets", so, it can be handled in 2 notable ways (current dir = "desktop/cs50/") :
cd psets then changing the relative address correspondingly in -I -L, so result:
gcc test-file.c -I../src -L../src -lcs50
keeping current directory same, but then changing the file's relative address correspondingly, so result:
gcc psests/test-file.c -Isrc -Lsrc -lcs50
or use absolute addresses 😜
as it can be seen that this becomes quite long, that's when build automation tools such as make kick in (though i am accomplishing that using a shell script 😜)