What is the difference between g++ and gcc?

What is the difference between g++ and gcc? Which one of them should be used for general c++ development?

gcc and g++ are compiler-drivers of the GNU Compiler Collection (which was once upon a time just the GNU C Compiler).

Even though they automatically determine which backends (cc1 cc1plus ...) to call depending on the file-type, unless overridden with -x language, they have some differences.

The probably most important difference in their defaults is which libraries they link against automatically.

According to GCC's online documentation link options and how g++ is invoked, g++ is equivalent to gcc -xc++ -lstdc++ -shared-libgcc (the 1st is a compiler option, the 2nd two are linker options). This can be checked by running both with the -v option (it displays the backend toolchain commands being run).

GCC: GNU Compiler Collection

• Referrers to all the different languages that are supported by the GNU compiler.

gcc: GNU C      Compiler
g++: GNU C++ Compiler

The main differences:

1. gcc will compile: *.c\*.cpp files as C and C++ respectively.
2. g++ will compile: *.c\*.cpp files but they will all be treated as C++ files.
3. Also if you use g++ to link the object files it automatically links in the std C++ libraries (gcc does not do this).
4. gcc compiling C files has fewer predefined macros.
5. gcc compiling *.cpp and g++ compiling *.c\*.cpp files has a few extra macros.

Extra Macros when compiling *.cpp files:

#define __GXX_WEAK__ 1
#define __cplusplus 1
#define __DEPRECATED 1
#define __GNUG__ 4
#define __EXCEPTIONS 1
#define __private_extern__ extern

For c++ you should use g++.

It's the same compiler (e.g. the GNU compiler collection). GCC or G++ just choose a different front-end with different default options.

In a nutshell: if you use g++ the frontend will tell the linker that you may want to link with the C++ standard libraries. The gcc frontend won't do that (also it could link with them if you pass the right command line options).

What is the difference between g++ and gcc?

gcc has evolved from a single language "GNU C Compiler" to be a multi-language "GNU Compiler Collection". The term gcc may still sometimes refer to the "GNU C Compiler" in the context of C programming.

man gcc

# GCC(1)                     GNU
# 
# NAME
#        gcc - GNU project C and C++ compiler

However, g++ is the C++ compiler for the GNU Compiler Collection. Like gnat is the Ada compiler for gcc. see Using the GNU Compiler Collection (GCC)

For example, the Ubuntu 16.04 and 18.04 man g++ command returns the GCC(1) manual page.

The Ubuntu 16.04 and 18.04 man gcc states that ...

> g++ accepts mostly the same options as gcc

and that the default ...

> ... use of gcc does not add the C++ library. g++ is a program > that calls GCC and automatically specifies linking against the C++ > library. It treats .c, .h and .i files as C++ source files instead of > C source files unless -x is used. This program is also useful when > precompiling a C header file with a .h extension for use in C++ > compilations.

Search the gcc man pages for more details on the option variances between gcc and g++.

Which one should be used for general c++ development?

Technically, either gcc or g++ can be used for general C++ development with applicable option settings. However, the g++ default behavior is naturally aligned to a C++ development.

The Ubuntu 18.04 'gcc' man page added, and Ubuntu 20.04 continues to have, the following paragraph:

> The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or machine-gcc-version to run a specific version of GCC. When you compile C++ programs, you should invoke GCC as g++ instead.

---

Side Note: In the case of the Xcode.app embedded toolchain, g++ simply links to gcc. Thus, g++ invocations may vary on a per-toolchain basis.

ls -l /Applications/Xcode.app/Contents/Developer/usr/bin
# …
# lrwxr-xr-x  1 root  wheel         3 Apr 27  2021 g++ -> gcc
# -rwxr-xr-x  1 root  wheel    167120 Nov 23 20:51 gcc

### -- versus --
which -a g++
# /usr/bin/g++
ls -l /usr/bin/g++
# -rwxr-xr-x  1 root  wheel  137616 Jan  1  2020 /usr/bin/g++

One notable difference is that if you pass a .c file to gcc it will compile as C.

The default behavior of g++ is to treat .c files as C++ (unless -x c is specified).

Although the gcc and g++ commands do very similar things, g++ is designed to be the command you'd invoke to compile a C++ program; it's intended to automatically do the right thing.

Behind the scenes, they're really the same program. As I understand, both decide whether to compile a program as C or as C++ based on the filename extension. Both are capable of linking against the C++ standard library, but only g++ does this by default. So if you have a program written in C++ that doesn't happen to need to link against the standard library, gcc will happen to do the right thing; but then, so would g++. So there's really no reason not to use g++ for general C++ development.

I became interested in the issue and perform some experiments

1. I found that description here, but it is very short.

2. Then I tried to experiment with gcc.exe and g++.exe on my windows machine:

    $ g++ --version | head -n1 
    g++.exe (gcc-4.6.3 release with patches [build 20121012 by perlmingw.sf.net]) 4.6.3
    
    $ gcc --version | head -n1
    gcc.exe (gcc-4.6.3 release with patches [build 20121012 by perlmingw.sf.net]) 4.6.3
   

3. I tried to compile c89, c99, and c++1998 simple test files and It's work well for me with correct extensions matching for language

    gcc -std=c99 test_c99.c
    gcc -std=c89 test_c89.c 
    g++ -std=c++98 test_cpp.cpp
    gcc -std=c++98 test_cpp.cpp
   

4. But when I try to run "gnu compiler collection" tool in that fashion:

    $ gcc -std=c++98 test_cpp.c
    cc1.exe: warning: command line option '-std=c++98' is valid for C++/ObjC++ but not for C [enabled by default]
   

5. But this one still work with no errors

    $ gcc -x c++ -std=c++98 test_cpp.c
   

6. And this also

    $ g++ -std=c++0x test_cpp_11.cpp 
   

p.s. Test files

$ cat test_c89.c test_c99.c test_cpp.cpp

// C89 compatible file
int main()
{
    int x[] = {0, 2};
    return sizeof(x);
}

// C99 compatible file
int main()
{
    int x[] = {[1]=2};
    return sizeof(x);
}

// C++1998,2003 compatible file
class X{};
int main()
{
    X x;
    return sizeof(x);
}

// C++11
#include <vector>
enum class Color : int{red,green,blue}; // scoped enum
int main()
{
    std::vector<int> a {1,2,3}; // bracket initialization
    return 0;
}

Findings:

1. If look at process tree then it seems that gcc, and g++ is backend to other tools, which in my environment are: cc1plus.exe, cc1.exe, collect2.exe, as.exe, ld.exe

2. gcc works fine as metatool for if you have correct extension or set correct -std -x flags. See this

“GCC” is a common shorthand term for the GNU Compiler Collection. This is both the most general name for the compiler, and the name used when the emphasis is on compiling C programs (as the abbreviation formerly stood for “GNU C Compiler”).

When referring to C++ compilation, it is usual to call the compiler “G++”. Since there is only one compiler, it is also accurate to call it “GCC” no matter what the language context; however, the term “G++” is more useful when the emphasis is on compiling C++ programs.

You could read more here.

I was testing gcc and g++ in a linux system. By using MAKEFILE, I can define the compliler used by "GNU make". I tested with the so called "dynamic memory" locating feature of "C plus plus" by :

int main(){

int * myptr = new int;
* myptr = 1;
printf("myptr[0] is %i\n",*myptr);
return 0;
}

Only g++ can successfully compile on my computer while gcc will report error

undefined reference to `operator new(unsigned long)'

So my own conclusion is gcc does not fully support "C plus plus". It seems that choosing g++ for C++ source files is a better option.

gcc and g ++ are both GNU compiler. They both compile c and c++. The difference is for *.c files gcc treats it as a c program, and g++ sees it as a c ++ program. *.cpp files are considered to be c ++ programs. c++ is a super set of c and the syntax is more strict, so be careful about the suffix.