g++ and gcc differences - g++

I am trying to compile CPP code on an Ubuntu machine. I read somewhere that g++ is included in gcc. so in CodeBlocks I included the GNU GCC compiler. Codeblocks returned an error saying that g++ was not found. Is g++ another seperate compiler?

g++ is for compiling C++, gcc is for compiling C. Two different compilers for two different languages!

I'm not very familiar with g++ but g++ is a C++ compiler and C++ is an extension of the C language so all C code can be compiled with a C++ compiler. So you could say that g++ contains a C compiler but saying that g++ contains gcc isn't correct I think.

Both g++ and gcc programs are from the same free software project, GCC. However, on Ubuntu you have several different packages for them, so install the g++-4.6 or the g++ package with gcc-4.6 or gcc one. (if you don't install both, you won't be able to compile both C & C++).
Both programs can compile C and C++ files, assuming the C files are suffixed with .c and the C++ ones with .cc or .cpp (etc..).
But they won't do exactly the same things, in particular, they won't link the same default libraries.
To understand what they do, you can run
gcc -v -Wall -g myprog.cc -o myprog
and
g++ -v -Wall -g myprog.cc -o myprog
and you'll see the differences. The -v flag often means "verbose".

Related

Is -std=c++2a necessary at link stage as well?

If I compile in two stages, using a particular language standard:
g++ -std=c++2a -c file1.cpp #compile source files
g++ -std=c++2a -c file2.cpp
g++ -std=c++2a file1.o file2.o -o program #link 'em
...can I leave the -std=c++2a out of the link command, or is it sometimes needed?
Version is gcc 10.
I guess you are compiling on Linux with a recent GCC. Be sure to read more about C++ and about your particular compiler (i.e. GCC 9 is not the same as GCC 10). Check with g++ --version what it is.
In practice you want to compile with warnings and debug information (in DWARF for GDB inside your ELF object files and executables), so use
g++ -std=c++2a -Wall -Wextra -g -c file1.cpp
and likewise for file2.cpp
Later (once your program is correct enough, e.g. has few bugs) you could want to ask the compiler to optimize it. So you could use
g++ -std=c++2a -Wall -Wextra -O3 -g -c file1.cpp
Practically speaking, you'll configure your build automation tool (e.g. GNU make or ninja) to run your compilation commands.
In rare cases, you could want to use link time optimizations. Then you need to both compile and link with g++ -std=c++2a -Wall -Wextra -O3 -g -flto and perhaps other options.
Be aware that link time optimization could almost double your build time.
You could also be interested by static analysis options of GCC 10 (or even by writing your own static analysis using GCC plugins).

Cross-platform static-linking SDL2

I'm building an SDL2/C++ program that needs to be portable to Windows, Mac, and Linux machines which may not have SDL installed.
I've read that static linking is the solution, but I'm not very good with compiling and don't know how to static link.
My program relies only on SDL2, GLU, and OpenGL. I'm compiling C++ with either MinGW (on Windows 8.1) or gcc (on Ubuntu 14.04) -- both of these OS's have SDL installed natively.
Here is my current makefile, derived from a sample makefile given to me by a professor of mine:
# Executable/file name
EXE=experiment
# MinGW
ifeq "$(OS)" "Windows_NT"
CFLG=-O3 -Wall -DUSEGLEW
LIBS= -lSDL2 -lglu32 -lopengl32
CLEAN=del *.exe *.o *.a
else
# OSX
ifeq "$(shell uname)" "Darwin"
CFLG=-O3 -Wall -Wno-deprecated-declarations
LIBS=-framework SDL2 -framework OpenGL
# Linux\Unix\Solaris
else
CFLG=-O3 -Wall
LIBS= `sdl2-config --cflags --libs` -lGLU -lGL -lm
endif
# OSX\Linux\Unix\Solaris
CLEAN=rm -f $(EXE) *.o *.a
endif
# Dependencies
$(EXE).o: $(EXE).cpp FORCE
.c.o:
gcc -c -o $# $(CFLG) $<
.cpp.o:
g++ -std=c++11 -c -o $# $(CFLG) $<
# Link
$(EXE):$(EXE).o
g++ -std=c++11 -O3 -o $# $^ $(LIBS)
# Clean
clean:
$(CLEAN)
# Force
FORCE:
To link with static library you either specify path to library file
gcc -o out_bin your_object_files.o path/to/lib.a -lfoo
or ask linker to use static version with -Bstatic linker flag. Usually you'll want to reset linking back to dynamic for the rest of the libraries, e.g. for static SDL2 and GLU but dynamic GL:
gcc -o out_bin your_object_files -Wl,-Bstatic -lSDL2 -lGLU -Wl,-Bdynamic -lGL
That of course implies that static versions of libraries are present in library search path list (.a libs for gcc on all specified platforms, although MSVC uses .lib for static libraries).
However you usually don't really want to do that at all. It is common practice for software to either depend on some libs (widespread on linux, with packages and dependendices lists) or bring required libraries with it. You can just distribute SDL dynamic library with your program and load it with LD_LIBRARY_PATH or relative rpath.
Please also note that newer SDL2 implements dynamic loading of functions which provides a way to override SDL with user-specified dynamic library, even if linked statically.
It wasn't related directly to static linking. When static linking, I had to include all of SDL's dependency libraries. Turns out, having -mwindows causes console communication to fail.

What is the signature of the Clang compiler in the ELF?

I have several binaries compiled with gcc/g++ and others compiled with clang/clang++.
So far i have tried:
strings -a ./myBinary | grep -i clang
objdump -s --section .comment ./myBinary
readelf -p .comment ./myBinary
and each one of this command fails to recognize the binaries produced by clang, and each file produced by Clang is recognized as produced by gcc and basically all my binaries are produced by the same compiler according to this tools.
Does Clang puts the same signature as GCC ? How i can get informations about what compilers have generated that binaries ?
Thanks.
I guess it's a duplicate of stackoverflow.com/questions/43523698/clang-appears-to-use-gcc
It seems that if you link against a glibc built by GCC, the latter takes the credits.

Problems when compiling Objective C with Clang (Ubuntu)

I'm learning Objective-C language. Since I don't have a Mac, I'm compiling and running my code within Ubuntu 11.04 platform.
Until now, I was using gcc to compile. I've installed GNUStep and all was working. But then I started to try some Objective-C 2.0 features, like #property and #synthesize, that gcc does not allow.
So I tried to compile the code with Clang, but it seems that it is not correctly linking my code with the GNUStep libraries, not even with a simple Hello world program.
For example, if I compile the following code:
#import <Foundation/Foundation.h>
int main(void) {
NSLog(#"Hello world!");
return 0;
}
The output of the compiler is:
/tmp/cc-dHZIp1.o: In function `main':
test.m:(.text+0x1f): undefined reference to `NSLog'
/tmp/cc-dHZIp1.o: In function `.objc_load_function':
test.m:(.text+0x3c): undefined reference to `__objc_exec_class'
collect2: ld returned 1 exit status
clang: error: linker (via gcc) command failed with exit code 1 (use -v to see invocation)
The command I'm using to compile is
clang -I /usr/include/GNUstep/ test.m -o test
with the -I directive to include the GNUStep libraries (otherwise, Clang is not able to find Foundation.h).
I've googled my problem, and visited both GNUStep and Clang web pages, but I haven't found a solution to it. So any help will be appreciated.
Thanks!
The problem was that the library gnustep-base was not being used by the linker. So the solution to this was using the option -Xlinker, that sends arguments to the linker used by clang:
clang -I /usr/include/GNUstep/ -Xlinker -lgnustep-base test.m -o test
The statement "-X linker -lgnustep-base" made the magic. However, I had problems with this command related to the class that represents a string in Objective-C:
./test: Uncaught exception NSInvalidArgumentException, reason: GSFFIInvocation:
Class 'NXConstantString'(instance) does not respond to forwardInvocation: for
'hasSuffix:'
I could solve it adding the argument "-fconstant-string-class=NSConstantString":
clang -I /usr/include/GNUstep/ -fconstant-string-class=NSConstantString \
-Xlinker -lgnustep-base test.m -o test
In addition, I've tried with some Objective-C 2.0 pieces of code and it seems to work.
Thank you for the help!
You can try gcc compiler:
First of all install GNU Objective-C Runtime: sudo apt-get install gobjc
then compile: gcc -o hello hello.m -Wall -lobjc
You are not able to use ObjC 2.0 features because you're missing a ObjC-runtime supporting those. GCC's runtime is old and outdated, it doesn't support ObjC 2.0. Clang/LLVM doesn't have a acompanied runtime, you need to install the ObjC2-runtime from GNUstep (which can be found here: https://github.com/gnustep/libobjc2 ) and reinstall GNUstep using this runtime.
Here are some bash scripts for different Ubuntu versions, that do everything for you:
http://wiki.gnustep.org/index.php/GNUstep_under_Ubuntu_Linux
And please don't try to reinvent GNUstep make, instead, use it:
http://www.gnustep.org/resources/documentation/Developer/Make/Manual/gnustep-make_1.html
If you really don't think so, here is some excerpt from there:
1.2 Structure of a Makefile
Here is an example makefile (named GNUmakefile to emphasis the fact that it relies on special features of the GNU make program).
#
# An example GNUmakefile
#
# Include the common variables defined by the Makefile Package
include $(GNUSTEP_MAKEFILES)/common.make
# Build a simple Objective-C program
TOOL_NAME = simple
# The Objective-C files to compile
simple_OBJC_FILES = simple.m
-include GNUmakefile.preamble
# Include in the rules for making GNUstep command-line programs
include $(GNUSTEP_MAKEFILES)/tool.make
-include GNUmakefile.postamble
This is all that is necessary to define the project.
In your case replace all occurrences of simple with test and you're done
1.3 Running Make
Normally to compile a package which uses the Makefile Package it is purely a matter of typing make from the top-level directory of the package, and the package is compiled without any additional interaction.

How to compile objc code on Linux?

Assuming you have your .h and .m ready on a Linux server, which command would you issue to GCC to have it compiled?
The relevant parts:
gcc -c -Wno-import List.m
gcc -o prog -Wno-import List.o main.o -lobjc
. . . make sure that the Objective-C library and header files (objc/Object.h) were installed when gcc was built.
Note that when linking Objective-C with gcc, you need to specify the Objective-C library by using the -lobjc switch.
See this link for more information.
Additional link with possible solution to the missing compiler issue:
Try installing either gobjc++ or gobjc
sudo apt-get install gobjc++
gcc -x objective-c file.m -o out
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