This might be the most newbie question ever, but how do you compile a C program?
I’ve downloaded the source of a C program (ffmpeg, to be precise). How do I compile it?
For most Unix-style C programs, the incantation is:
./configure
make
sudo make install
This should already be documented in the INSTALL file, which additionally may contain further useful information.
For a single file just cc file.c (or gcc or whatever you C compiler is called)
For a complex project like ffmpeg, then either make, cmake, configure some other. Check their documentation
It depends on what OS and compilers you have, but typically the sequence is:
$ ./configure
$ make
$ sudo make install
to compile simple math program, it's not enough to <include math.h>. See
gcc file.c -lmath -o program_bin
for a single .c file using ffmpeg libraries, it can be made this way:
gcc -Wall -g live_segmenter.c -o live_segmenter -lavformat -lavcodec -lavutil -lbz2 -lm -lz -lfaac -lmp3lame -lx264 -lfaad -lpthread -I/home/devicer/ffmpeg/include -L/home/devicer/ffmpeg/lib
notice -L and -I options. In serious projects they are usually set by pkg-config.
for the ffmpeg itself..
- install lame, few other required libraries, then do as Chris said.
Btw, sometimes it requires gmake, not make.
Also, have a look on
./configure --prefix /home/devicer/ffmpeg
This is what was mentioned (used for) in segmenter compilation above.
Related
I have a file called "speed.c" which I wish to use for a web program
This works:
gcc speed.c -lcrypto -lssl
But this doesn't:
emcc speed.c -v -lcrypto -lssl -s EXPORTED_FUNCTIONS=_speed,_main -o speed.wasm
The function within speed.c is called "speed".
On the website for Emscripten, it says that the compiler is just like any other so this one confuses me.
Any help? Thanks!
Emscripten can't use you system's libraries. This is because they are binaries compiled for your own machine (probably 64-bit linux), while emcc compiles to WebAssembly/JavaScript. You can generally see what architecture a binary is targeting with file:
$ file `realpath /usr/lib/libssl.so`
Thus, you will need to first compile OpenSSL with emcc. I haven't done this myself, but I believe it's possible. You could check out this github issue.
Once you've done that you should have two files name libssl.a and libcrypto.a. Then you can compile your own project like this:
$ SSL=/path/to/openssl
$ emcc speed.c $SSL/libssl.a $SSL/libcrypto.a -I $SSL/include/ # etc.
Take a look at the project building page if you haven't yet.
I'm running a Debian (Buster) container and my goal is to compile a small program I wrote which relies on libgit2. First, I was installing libgit2 via the libgit2-dev package and my Makefile had the following:
gcc -O2 -fpic -shared -I /usr/local/include -lgit2 -o output.so my_app.c
However, I'd rather have a "cleaner" environment and install libgit2 via the libgit-27 which, AFAIK, only installs the shared object binary instead of also including the development files like libgit2-dev does.
Using find I can find where the .so file is installed into:
$ find / -name "*git2*" -print 2>/dev/null
/usr/lib/x86_64-linux-gnu/libgit2.so.0.27.7
/usr/lib/x86_64-linux-gnu/libgit2.so.27
/usr/share/doc/libgit2-27
/var/lib/dpkg/info/libgit2-27:amd64.list
/var/lib/dpkg/info/libgit2-27:amd64.symbols
/var/lib/dpkg/info/libgit2-27:amd64.md5sums
/var/lib/dpkg/info/libgit2-27:amd64.shlibs
/var/lib/dpkg/info/libgit2-27:amd64.triggers
and I've been trying several combinations of linking this .so with gcc like:
gcc -O2 -fpic -shared -L /usr/lib/x86_64-linux-gnu/ -libgit2.so.27 -o output.so my_app.c
but so far I always get the following error:
my_app.c:1:10: fatal error: git2.h: No such file or directory
#include <git2.h>
^~~~~~~~
compilation terminated.
I understand this is a glaring lack of knowledge on how C compilation works. My two questions are:
Is it possible to compile my program by just relying on the libgit2-27 Debian Buster package instead of libgit2-dev? If not, why?
If yes, an example and explanation would be appreciated!
I've used linuxbrew to install gcc 5.3 on a machine on which I don't have sudo access. I now want to link with X11:
> gcc test.c -lX11
ld: cannot find -lX11
I've checked that libX11.so exists in /usr/lib64/ which is on the compiler's LIBRARY_PATH. If I use the system's gcc it works fine, but I need a newer version to compile my actual program.
use -L flag, like this -L/usr/lib64, or you can specify full path to library like this gcc test.c /usr/lib64/libX11.so
According to this comment by a linuxbrew developer,
linuxbrewed gcc removes /usr/lib64 from the library path because mixing system libraries with brewed libraries creates havoc.
The solution is to brew install linuxbrew/xorg/xorg.
I'm trying to use liboauth with a C program, using gcc as my compiler, and no matter what I've tried I keep getting the error "ld: library not found for -loauth" and "clang: error: linker command failed with exit code 1".
I'm including the header via "#include <oauth.h>", and my most-recent call to gcc looked like this:
gcc -Wall -lcurl -loauth -I /usr/local/include -v -o api api.c
Now, oauth.h does exist in /usr/local/include, and there are a handful of liboauth files (including liboauth.a) located in /usr/local/bin, which I'm assuming were placed there when I ran the install. I will admit that I'm not very familiar with gcc and compiling non-trivial C programs, but I was able to get libcurl working on a fresh download in just a few minutes. I just can't figure out what's going on with liboauth.
Thanks in advance
If you are sure liboauth's located in /usr/local/bin use
gcc -Wall -L/usr/local/bin -I /usr/local/include -v -o api api.c -lcurl -loauth
It'd also be better to place libraries in the end of the command as there is some important stuff with them (they may depend on each other, etc).
By the way, it's pretty strange your libraries are in /usr/local/bin as libraries are almost always stored in some path like /usr/*/lib.
I'm trying to compile the following project on a remote server.
I've git cloned the project on a folder called 'scode'.
The project requires glib2 and gsl libraries. Since I'm trying to compile on a remote server, I do not have sudo privileges. So I can't use a tool to install glib2 and gsl for me.
As a result, I've manually compiled both gsl and gslib2 under the folders 'scode/gsl' and 'scode/glib'.
I've had to modify the Makefile and add absolute paths to these directories as -I options.
Nonetheless, when I try to compile the final executable. I get the following error:
[dyuret#psglogin scode]$ make
gcc -O3 -D_GNU_SOURCE -Wall -std=c99 -I. -I /home-2/dyuret/scode/gsl
-I /home-2/dyuret/scode/glib/ pkg-config --cflags glib-2.0 scode.o svec.o pkg-config --libs glib-2.0 -lm -lgsl -lgslcblas -o scode
//home-2/dyuret/scode/glib/glib/libglib-2.0.la: file not recognized:
File format not recognized
collect2: error: ld returned 1 exit status make: * [scode] Error 1
I've researched the issue a bit. This link looks informative but I can't quite decipher what the author is saying, as I'm not that experienced with compilers, libtools and the compilation flow in general.
Any help would be much appreciated. I've already spent some time on this issue and I haven't been able to make much progress.
It sounds as if what you did in order to compile the libraries in non-default (i.e. non-system) locations was maybe wrong.
For packages using autoconf (i.e. that have a configure script in the source root) you're supposed to use the --prefix option to ./configure to set the target location where you want the package installed.
With packages building shared libraries, it's often essential to do the make install step, which it sounds as if you maybe didn't do.
Sorry for being vague, these things are a bit complicated.
Someone at my group helped me with the problem. Here're the steps he roughly carried out:
(1) Manually installed glib and additional libraries at $HOME directory - i.e. $HOME/lib, $HOME/include.
(1.1) I think he did this by './configure prefix=$HOME', 'make', 'make install'.
(2) Got rid of `pkg_config` usage, which was causing the problem I outlined originally. Here are his new CLFAGS and LIBS variables:
CFLAGS=-O3 -D_GNU_SOURCE -Wall -std=c99 -I. -I$$HOME/include -I$$HOME/include/glib-2.0 -I$$HOME/lib/glib-2.0/include
LIBS=-lglib-2.0 -lm -lgsl -lgslcblas -L$$HOME/lib -L/usr/local/cuda/lib64 -lcudart
After this, the code compiled without additional problems.