I was wondering about the standard C libraries that contain all the functions/definitions like abs(), cout streams, printf, etc.
I'm familiar with the header files (stdio.h, cmath.h, time.h, etc etc) but there doesn't seem to be any corresponding .lib or .dll anywhere (ie. stdio.lib, time.dll, etc).
Where is the actual code for the functions in these header files? Am I misunderstanding something? Is there like, one huge lib file that contains all the standardized stuff, or one for each header?
Any help appreciated!!
Thanks!
It depends on the implementation. On Windows, the standard library functionality is in the C and C++ runtime libraries. The C runtime library is always linked in automatically; the C++ runtime library is linked in automatically if you include one of the standard library headers.
If you are on Linux/some variant of UNIX/AIX try using ldd . Just for the fun of trying something new type in ldd `which ls` in your Linux prompt. Here's what I got:
librt.so.1 => /lib/tls/librt.so.1 (0x0084c000)
libacl.so.1 => /lib/libacl.so.1 (0x40022000)
libselinux.so.1 => /lib/libselinux.so.1 (0x00289000)
libc.so.6 => /lib/tls/libc.so.6 (0x00a0b000)
libpthread.so.0 => /lib/tls/libpthread.so.0 (0x00c57000)
/lib/ld-linux.so.2 (0x009ec000)
libattr.so.1 => /lib/libattr.so.1 (0x40028000)
The paths should tell you where from the shared libraries are being picked up.
If you are using Windows, get hold of depends.exe http://www.dependencywalker.com -- excellent tool
You generally don't have to explicitly link the C or C++ runtime libraries in. Usually the compiler will call the linker with the correct options to do it for you.
In fact, with gcc, you have to do something to not include the default libraries (such as using -nodefaultlibs, -nostdlib or -nostartfiles).
The actual location of the standard library, including whether or not it's in a single file, is an implementation issue.
As Arpan mentioned, you can use ldd (which is in the 'binutils' package) to discover what SO file is actually being used for libc. The most common implementation on Linux systems is the GNU C library, usually called glibc.
If you mention DLL's, I assume you are using Windows. In this case, there is usually one "runtime" DLL shipped with compiler. With Visual C++, I believe the name is msvcrt.dll or similar.
Related
For the case of GCC and linux,
I wonder
if C++ library depends on C library API.
if C library includes every system calls.
if C++ library includes every system calls.
if there exist any system library which provide system calls other than C/C++ library. (I believe pthread library prodives some posix thread API)
Thank you in advance.
if C++ library depends on C library API.
for GNU C, yes. It might be beneficial to do it that way, because a lot of C standard library functions are part of the C++ standard as well.
if C library includes every system calls.
It doesn't "include" a single one, because a system call is something exposed by the kernel. What A C library does is provide some wrappers around system calls, but no, not necessarily around all of them. There are helpers to call syscalls for which no wrapper is provided. Maybe start reading here: syscalls(2).
if C++ library includes every system calls.
See above.
if there exist any system library which provide system calls other than C/C++ library. (I believe pthread library prodives some posix thread API)
Yes (adding the word "wrappers" to your wording) and you already named an example. Note the POSIX thread API doesn't require kernel level threads, but it's implemented using them on Linux.
Yes, the GNU C++ library is linked with the GNU C library.
$ ldd /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.20
linux-vdso.so.1 => (0x00007ffc1b5bc000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fb25239c000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb251fd2000)
/lib64/ld-linux-x86-64.so.2 (0x00007fb2529b3000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fb251dbc000)
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I know that on Windows, you get some libraries linked in by default to your process- like kernel32.dll, etc. Are there any equivalent libraries on Linux?
I am creating some Linux binaries and looking for support routines, especially malloc, etc. On Windows I simply implemented malloc() on top of HeapAlloc (which is also the approach taken by the VS CRT) but I'm not sure what to do here. For reasons, I'm not going to link to libc when creating the binary if at all possible.
By default, G++ in Linux will link against the C standard library and C++ standard library. Occasionally it will also bring in the math library automatically, although historically you need to ask for that with -lm.
On my Ubuntu box, I compiled and linked the following simple "Hello World" app:
#include <iostream>
int main()
{
std::cout << "Hello world!" << std::endl;
}
I compiled it as follows: g++ hello.cpp
The ldd utility lists the libraries g++ linked this against:
$ ldd a.out
linux-vdso.so.1 => (0x00007fff1d344000)
libstdc++.so.6 => /usr/local/lib64/libstdc++.so.6 (0x00007fd7fb031000)
libm.so.6 => /lib/libm.so.6 (0x00007fd7fadae000)
libgcc_s.so.1 => /usr/local/lib64/libgcc_s.so.1 (0x00007fd7fab97000)
libc.so.6 => /lib/libc.so.6 (0x00007fd7fa813000)
/lib64/ld-linux-x86-64.so.2 (0x00007fd7fb365000)
The first line, linux-vdso.so.1 isn't actually a library. Google it if you want to learn about some magic hackery. The rest are pretty pedestrian:
libstdc++ is the C++ standard library
libm is the aforementioned math library. I don't know if C++ includes it by default, but historically the C compiler did not include it unless you specified -lm at link time.
libgcc_s is a GCC-specific support library, containing various support routines (ie. for oddball things like oddball divides, structure-copies, etc.)
libc is the C standard library. It also contains a lot of POSIX functionality.
ld-linux-x86-64 is the dynamic library loader. This is actually an executable.
So, that's the default bit of kit.
Pieces such as malloc, new, printf, etc. are all in there, along with the full C++ standard library (what some call the "STL").
If you're asking what support comes by default, this is it. If you're trying to implement your own versions of these things... the -nodefaultlibs flag will let you. You might also need -ffreestanding and maybe even -fno-builtins.
If you want to see how these pieces are built (including how glibc calls mmap and/or sbrk to get memory to populate a malloc heap), you can download the source for glibc and take a look. There isn't a level below glibc you can target directly other than making system calls directly.
Assuming you're building your code with GCC / G++, you may need to include some of these libraries, such as libgcc_s and libstdc++. You might be able to limit / eliminate your dependence on libstdc++ if you refrain from using standard library functions, and build with -ffreestanding. But, I'll be honest: I only know of the flag, I've never used it.
I think you want some lower level API for memory management. Then this question might help you.
It suggests mmap function. It hope it might help you.
According to ldd The following libraries are linked by default with g++ 4.8 on my ubuntu linux machine for basic c++ programs.
linux-vdso.so.1 => (0x00007fffe11fe000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f1d1e49b000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f1d1e285000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f1d1debc000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f1d1dbb8000)
/lib64/ld-linux-x86-64.so.2 (0x00007f1d1e7c7000)
You can disable linking them using -nodefaultlibs switch but you also need to specify that they need to be linked later using the appropriate switches.
On Linux, glibc is equivalent of a lot of stuff in the Windows libraries. The POSIX C interface functions, including the C standard library and also the kernel system call wrappers are all in libc. It is the primary wrapper layer providing ABI compatibility between various kernel versions. Not using it is very stupid.
The Windows CRT indeed has a different status, because POSIX has a different status on Windows. Where the Win32 API provides the OS interface on Windows, it is POSIX (including the C stdlib!) on Linux.
When on Linux, link glibc.
You will also need to link some compiler support library, be it LLVM's compiler-rt or GCC's libgcc.
I have CentOS 6.2 (64bit with gcc 4.4.6 as default). Unfortunately, my code only compiles with gcc 3.4.6, so I installed gcc separately (from source) under /home/rajat/local. On linking a simple "Hello World" program, I get the following.
>ldd a.out
linux-vdso.so.1 => (0x00007fff215ff000)
libstdc++.so.6 => /home/rajat/local/lib64/libstdc++.so.6 (0x00007f11853e7000)
libm.so.6 => /lib64/libm.so.6 (0x00000033be400000)
libgcc_s.so.1 => /home/rajat/local/lib64/libgcc_s.so.1 (0x00007f11851ce000)
libc.so.6 => /lib64/libc.so.6 (0x00000033bd000000)
/lib64/ld-linux-x86-64.so.2 (0x00000033bcc00000)
While stdc++ and gcc link to my 3.4.6 libraries, libm and libc still link to default libraries. Is this OK?? The 3.4.6 installation also did not produce libm or libc libraries?
Yes, that's ok.
The libc/libm is part of glibc, not the gcc compiler. libstdc++ on the other hand ls part of gcc.
Libraries in /lib and /usr/lib as well as their 64-bit counterparts are system-wide libraries. They are supposed to be compiler neutral and other compilers besides GCC can also link to them and they actually do, especially since libc is the only portable way to interface with the operating system kernel.
libc writers take great care of writing their header files in such a way as to make different compilers produce the same binary memory objects in order to properly interface with the code in the library. Besides, there is a well-defined OS ABI interface that all compilers adhere to in order to be compatible with one another. This might not be true for languages other than C, e.g. object files from different C++ compiler versions rarely go well with one another.
Compiler-specific libraries are not installed in /lib or /usr/lib and sometimes can be linked statically so that the dependency can be removed.
I have a requirement that I link all my libraries statically including libstdc++, libc, pthread etc. There is one omniorb library which I want to link dynamically.
Currently I have dynamically linked all the libraries.
ldd shows the following
linux-vdso.so.1 => (0x00007fff251ff000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f291cc47000)
libomniDynamic4.so.1 (0x00007f291c842000)
libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00007f291c536000)
libm.so.6 => /lib64/libm.so.6 (0x00007f291c2e0000)
libgomp.so.1 => /usr/lib64/libgomp.so.1 (0x00007f291c0d7000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f291bebf000)
libc.so.6 => /lib64/libc.so.6 (0x00007f291bb66000)
/lib64/ld-linux-x86-64.so.2 (0x00007f291ce63000)
librt.so.1 => /lib64/librt.so.1 (0x00007f291b95d000)
libomniORB4.so.1 (0x00007f291b6aa000)
libomnithread.so.3 (0x00007f291cf35000
I need ldd to show libomniDynamic4.so.1 as the only dynamically linked library.
How do I achieve this?
Trying to make a linux executable that runs on all distros eh? Good luck...But I digress...
You want to look at the -v flag output for g++. It shows the internal link commands executed by g++/ld. Specifically, you'll want to inspect the the final link command collect2 and all of its arguments. You can then specify the exact paths to the .a libs you want to link against. You'll also have to track down static libs of everything. My libstdc++.a is in /usr/lib/gcc/x86_64-linux-gnu/4.4/libstdc++.a
rant on: My biggest complaint about linux is the fractured state of executables. Why cant I compile a binary on one machine and copy it to another and run it!? Even the Ubuntu distros one release apart will produce binary files that cannot be run on the other due to libc/libstdc++ ABI incompatibilites
edit #1 I just wanted to add that The script on this page produces a .png of an executables .so dependencies. This is very useful when attempting to do what you describe.
Be aware ldd <exename> will list all dependencies down the chain, not just immediate dependencies of the executable. So even if your executable only depended upon omniorb.so, but omniorb.so depended upon, libphread.so, ldd's output would list that. Look up the manpage of readelf to find only the immediate dependencies of a binary.
One other item that to be aware of. if omniorb.so depends upon libstdc++.so, you'll have no choice but to be dependant on that same lib. Otherwise ABI incompatibilities will break RTTI between your code and omniorb's code.
I need ldd to show libomniDynamic4.so.1 as the only dynamically linked library.
That is impossible.
First, ldd will always show ld-linux-x86-64.so.2 for any (x86_64) binary that requires dynamic linking. If you use dynamic linking (which you would with libomniDynamic4.so.1), then you will get ld-linux-x86-64.so.2.
Second, linux-vdso.so.1 is "injected" into your process by the kernel. You can't get rid of that either.
Next, the question is why you want to minimize use of dynamic libraries. The most common reason is usually mistaken belief that "mostly static" binaries are more portable, and will run on more systems. On Linux this is the opposite of true.
If in fact you are trying to achieve a portable binary, several methods exist. The best one so far (in my experience) has been to use apgcc.
It is very difficult to build a single binary that runs on a lot of Linux distros and linking statically is not the key point.
Please note that a binary built with an older glibc version--i.e., an old Linux distro--may run on newer Linux distros as well. This works because glibc is back-compatible.
A possible way to attain the desired result is:
compile the binary on an old Linux OS
find out all the required libraries for your compiled binary using the command ldd or lsof
(when running) on the binary, details here
copy the required libraries of the old Linux OS in a 'custom-lib' folder
always bundle/release this custom-lib folder with your binary
create a bash script that puts the custom-lib folder on top of the folders list in LD_LIBRARY_PATH environment variable, and then invokes your binary.
In this way, by executing the binary with the bash script, I was able to execute binaries on a wide range of embedded devices with very different Linux versions.
But there are always problematic cases where this fails.
Please note, I always tested this with cli applications/binaries.
Other possible ways..
There also seems to be elegant ways to compile glibc-back-compatible binaries, for example this that seems to compile binaries compatible with older ABI. But I have not checked this route.
when linking, use -static before specifying the libraries you want to link statically to, and use -dynamic before the libraries you want to link dynamically to. You should end up with a command line looking like this:
g++ <other options here> -dynamic -lomniDynamic4 -static -lpthread -lm -lgomp <etc>
Of course, you'll need .a versions of the libraries you want to link statically (duh).
I know this might be a very stupid question but I am new to compiled languages (my domain is mostly scripting languages like PHP, Python or JavaScript).
I am learning C++ for one project where it is the only language I can use.
I wrote a program in Ubuntu 10.10 and then compiled it. I can run the generated binary file from cmd like this and it works:
sudo ./compiled-program
But, I have used some external libraries in the program (OpenCV). Does that mean that all computers where I will run the program will have to have OpenCV installed? Or is OpenCV bundled inside the compiled binary file? Will it work on PCs without OpenCV installed?
You should read a few things about libraries, and particularly what makes the difference between static and dynamic libraries. To quote the basic definitions so you get the point :
A static library, also known as an
archive, consists of a set of routines
which are copied into a target
application by the compiler, linker,
or binder, producing object files and
a stand-alone executable file.
[...]
Dynamic linking involves loading the
subroutines of a library (which may be
referred to as a DLL, especially under
Windows, or as a DSO (dynamic shared
object) under Unix-like systems) into
an application program at load time or
runtime, rather than linking them in
at compile time.
Not a stupid question at all!
The "normal" way this works - is that your program has been linked against a "Shared Library" - in which case, yes, the user needs the OpenCV (or whatever bundle includes the shared library) to work.
If you compiled as a static executable, (using the -static) flag, then it, and all libraries would be included directly into your executable, making a bit of a larger executable that wastes more memory, because it isn't using a shared library.
There are ways that you could compile your program to link only your OpenCV libraries as static - but that only can be done if the bundle included a static library ".a" vs. a shared one ".so".
If you had to build your code against dependencies, like OpenCV, it depends on if you did static or dynamic linking.
See here which has sections covering these ideas: http://en.wikipedia.org/wiki/Library_(computing)
For starters, try doing this on the command line:
ldd compiled-program
You will get output like this (as an example, I did ldd on my python binary in /usr/bin):
birryree#lilun:/usr/bin$ ldd python
linux-gate.so.1 => (0xb7ff7000)
libpthread.so.0 => /lib/i686/cmov/libpthread.so.0 (0xb7fd5000)
libdl.so.2 => /lib/i686/cmov/libdl.so.2 (0xb7fd1000)
libutil.so.1 => /lib/i686/cmov/libutil.so.1 (0xb7fcd000)
libssl.so.0.9.8 => /usr/lib/i686/cmov/libssl.so.0.9.8 (0xb7f82000)
libcrypto.so.0.9.8 => /usr/lib/i686/cmov/libcrypto.so.0.9.8 (0xb7e2a000)
libz.so.1 => /usr/lib/libz.so.1 (0xb7e16000)
libm.so.6 => /lib/i686/cmov/libm.so.6 (0xb7df0000)
libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb7caa000)
/lib/ld-linux.so.2 (0x80000000)
Python wants a lot of additional stuff, like libssl (part of OpenSSL), the GNU C library (libc), and some others.
Now if you're going to be moving this thing around to other systems, you either hope they have an environment similar to yours, distribute it as source and use something like the autotools/GNU Build System to build it, or you can forego all that and statically link everything into your binary, which will bring in all the stuff your executable needs without need for a dynamic link.
If you've "compiled against" OpenCV, then machines running your app need it too. You need to copy the libs when you install your app, or ensure that they're already installed.
It depends on wether you are compiling against a shared (Dynamic) library or compiling it into your executable (compiling against a static library). If you are compiling against a shared library you need to distribute the shared library ... otherwise .. you don't.
There are two kinds of libraries, static and dynamically loaded.
Statically loaded libraries are joined with your binary file, while dynamically loaded libraries are loaded at runtime.
It depends on whether or not the executable is statically-built or dynamically linked. In a statically-built executable it is the case that the library files the executable needs are compiled into the executable and there isn't an need to carry around additional library files. In a dynamically linked executable it is the case that the library files the executable needs are linked at runtime and therefore a copy of the library files are needed at runtime.