I have some example C code that I'm looking to adapt to suit my needs. Before then I'm trying to compile the example as it is. The C code contains a #include reference, and I can find the .h file in an 'inc' directory. There is also a corresponding 'lib' directory. I am struggling to find the command line I need to compile the code.
So far I've managed to get to the following;
gcc -o amqsinqa -I/opt/mqm/inc amqsinqa.c -L/opt/mqm/lib -lcmqc
But it 'cannot find -lcmqc'. I've looked in lib and quite correctly there is no cmqc. How do I determine what -l option I need here?
The code looks fairly simple, there is the include reference;
#include <cmqc.h>
And the call itself;
MQCONN(QMgrName,&Hcon,&CompCode,&CReason);
If I omit the -l option from the command line I get;
undefined reference to 'MQCONN'
Which isn't a surprise. MQCONN is present in cmqc.h though.
To try to help others, this reference is useful:
64 bit apps: https://www.ibm.com/support/knowledgecenter/en/SSFKSJ_9.1.0/com.ibm.mq.dev.doc/q028490_.htm
32 bit apps:
https://www.ibm.com/support/knowledgecenter/SSFKSJ_9.1.0/com.ibm.mq.dev.doc/q028480_.htm
In summary:
-I is for the product includes, which are (For Linux) usually in /opt/mqm/inc
-L is the path to the libraries in your example which are (For Linux) usually in /opt/mqm/lib (for 32 bit applications) and /opt/mqm/lib64 (for 64 bit
applications)
-l (lower case L) is for the required library/libraries,
and the actual library you need is either:
mqm - server bound C applications (ie -lmqm, which links with libmqm.so)
mqic - client bound C applications (ie -lmqic, which links with libmqic.so)
.. and a suffix of _r if you are building as a threaded application (ie you are linking with -lpthread as well, ie providing -lmqm_r or -lmqic_r which in effect links with libmqm_r.so or libmqic.so)
cmqc.h is the name of the main header file, and there are other cmq*.h headers you can optionally include as well.
If you are using the (stabilized) C++ libraries there's other libraries to include on the command line but that's outside the scope for this answer - see the referenced links
Thanks to all the above for the guidance. Looks like I was missing a few things. This is what I did;
Use nm to identify which .so file contained what I wanted. This returned libmqm.so.
Move that into the -l command, which gave me;
gcc -o amqsinqa -I/opt/mqm/inc amqsinqa.c -L/opt/mqm/lib -lmqm
But it left me with a 'skipping incompatible' warning message followed by a 'cannot find' error message.
Most common Google answer to this issue was a 32/64 bit mismatch, so I searched for a 64 bit version of the same, which ended up being in lib64. So the final compile command is;
gcc -o amqsinqa -I/opt/mqm/inc amqsinqa.c -L/opt/mqm/lib64 -lmqm
You should review the gcc options, in particular the '-m' option,
If you want to build a 32-bit MQ application then you do:
gcc -m32 -o amqsinqa -I/opt/mqm/inc amqsinqa.c -L/opt/mqm/lib -lmqm
If you want to build a 64-bit MQ application then you do:
gcc -m64 -o amqsinqa -I/opt/mqm/inc amqsinqa.c -L/opt/mqm/lib64 -lmqm
I'm using OSX command line gcc and attempting to build a dynamic library. when I do the build I get the following warning. How is it it is not finding this library given /usr/lib is well known? And /usr/lib does indeed exist on my machine
this is what I am using:
gcc -arch i386 cata/*.c -dynamiclib -o build/cata.dylib -LC_ID_DYLIB=/usr/lib
Thanks
the way i solved it was to make it so the string that got stuck in the library (on where to find the library at runtime) was relative to nowhere -- if that makes sense. so it would be forced to use the LD_LOAD_PATH.
I was using the other flags because someone suggested I use them.
so the gcc i ended up using is this:
# my tree is like this
# cata/*.c
# build/*.dylib
#
cd build
gcc -arch i386 ../cata/*.c -dynamiclib -o cata.dylib
Doing this compiles/makes a library in the same directory where it thinks it is 'used' (basically having no path). I am now free to put it somewhere else. When it is later linked at compile time by a different program and then examined using
otool -L
it appears with no path in front of the library name. This is apparently preferable as now when the system goes to try to find it it resorts to looking at the standard libraries and eventually finds it (because I install it to one of the standard locations).
In the original way, otool -L was showing it having a required path of
'build/cata.dylib'
This made it un-findable and which is why i was trying to use the apple documentation to get around the problem.
This doesn't really solve why LC_ID_DYLIB doesn't work. I looked into the Loader.h file (line 643) and it has room for an identifier(0xd), a path, and a structure, so I don't really understand why my path wasn't getting picked up. but its two different topics. Loader.h is runtime and the other is gcc AFAIK. I'm still learning apple.
From the docs:
CPATH specifies a list of directories to be searched as if specified with -I, but after any paths given with -I options on the command line. This environment variable is used regardless of which language is being preprocessed.
On my machine, I'd like to e.g. cross-compile or, otherwise have an versioned set of alternative includes. I'd like to use those to compile other people's code.
Concretely, I have several different versions of python, and their related Python.h files.
$ python setup.py pillow
fails because the include it finds first isn't the one needed.
(/usr/local/include has an old Python.h, but I need /usr/local/include/Python2.7 to "win").
Adding /usr/local/include/Python2.7 to CPATH (or C_INCLUDE_PATH) doesn't work because it's placed later.
As far as I can see, this isn't python-specific -- surely there's a way to force GCC to have paths prior to -I / CPATH?
Its a bit hacky, but you can add it to your compiler var
Makefile syntax
CC = gcc -Ipath
Or
export CC="gcc -Ipath"
Or g++ for the CXX variable.
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 😜)
I don't get it. I usually install third party software into /usr/local so libraries are installed into /usr/local/lib and never had problems linking to these libraries. But now it suddenly no longer works:
$ gcc -lkaytils -o test test.c
/usr/bin/ld.gold.real: error: cannot find -lkaytils
/usr/bin/ld.gold.real: /tmp/ccXwCkYk.o: in function main:test.c(.text+0x15):
error: undefined reference to 'strCreate'
collect2: ld returned 1 exit status
When I add the parameter -L/usr/local/lib than it works but I never had to use this before. Header files in /usr/local/include are found without adding -I/usr/local/include.
I'm using Debian GNU/Linux 6 (Squeeze) which has an entry for /usr/local/lib in /etc/ld.so.conf.d/libc.conf by default and the ldconfig cache knows the library I'm trying to use:
k#vincent:~$ ldconfig -p | grep kaytils
libkaytils.so.0 (libc6,x86-64) => /usr/local/lib/libkaytils.so.0
libkaytils.so (libc6,x86-64) => /usr/local/lib/libkaytils.so
So what the heck is going on here? Where can I check which library paths are searched by gcc by default? Maybe something is wrong there.
gcc -print-search-dirs will tell you what path the compiler checks. /usr/local/lib is simply not among them, so your compile time linker (in this case the new gold ld from binutils) doesn't find the library while the dynamic one (ld-linux.so which reads the cache written by ldconfig) does. Presumably the builds you've done previously added -L/usr/local/lib as necessary in their makefiles (usually done by a ./configure script), or you installed binaries.
This is probably an issue of environment variables - you have something set that's including /usr/local/include but not /usr/local/lib
From the GCC mapage on environment variables
CPATH specifies a list of directories to be searched as if speci‐
fied with -I, but after any paths given with -I options on the com‐
mand line. This environment variable is used regardless of which
language is being preprocessed.
and
The value of LIBRARY_PATH is a colon-separated list of directories,
much like PATH. When configured as a native compiler, GCC tries
the directories thus specified when searching for special linker
files, if it can’t find them using GCC_EXEC_PREFIX. Linking using
GCC also uses these directories when searching for ordinary
libraries for the -l option (but directories specified with -L come
first).
try "printenv" to see what you have set