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.
Related
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.
Resently I'm installed Opencv in my machine. Its working in python well(I just checked it by some eg programs). But due to the lack of tutorials in python I decided to move to c. I just run an Hello world program from http://www.cs.iit.edu/~agam/cs512/lect-notes/opencv-intro/
while compiling I got the following error
hello-world.c:4:16: fatal error: cv.h: No such file or directory
compilation terminated.
I'm new in opencv
Qn : Could you please report what may be the problem - and how I run my helloworld program in c?
Your compiler cannot find your cv.h include file. If you installed from your package manager, it is probably in /usr/include/opencv/. You need to add that your include search path. If you are compiling from the command line use -I to specify additional include directories. It will be something like -
gcc -I /usr/include/opencv/ -o helloworld helloworld.c
If you are using Eclipse,
Right click on the project and select properties.
Select C/C++ General -> Path and Symbols.
Select Includes tab.
In Languages list, select 'GNU C' or 'GNU C++' depending on which you are using.
Press 'Add...' button and add /usr/include/opencv/
Save and rebuild.
You need to show compiler path to cv.h file. The quick way to find it is to do (on Ubuntu):
find /usr -name "cv.h"
/usr/local/include/opencv/cv.h
Just add this to the compiler:
gcc -I/usr/local/include/opencv -o helloworld helloworld.c
Since you asking this question your compiler might also have problems linking your program to opencv libraries. Just do the same thing only for library files:
find /usr -iname "libopencv*"
/usr/local/lib/libopencv_flann.so
...
add this folder the same way and specify libraries you want to use:
gcc helloworld.c -I/usr/local/include/opencv -L/usr/local/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -o helloworld
that should probably compile. There is a also a short cut you can take and instead of all that steps just use the following command
gcc helloworld.c `pkg-config --cflags --libs opencv` -o helloworld
that should take care of all the work of locating required files for you and let you focus on the fun coding part.
maybe you just installed the opencv package.
But, as you want to use opencv in your C program, you may also install the package named just like opencv-devel. If you haven't, install it and than use it as #iagreen said.
Best wishes to you.
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.